Colorado Gardening Calendar for May 2024

By Valerie Podmore – CSU Extension-Denver Master Gardener since 2020

This is the month we’ve been waiting for! May is the best month for getting your plants from the Master Gardener Plant Sale on the 18^th and 19^th and planting them, with the caveat that anything can happen weather-wise, so be ready…remember 2 years ago?

Vegetable Garden

• This is the time to direct sow hardy, cool season vegetable seeds such as lettuce, kale, and spinach.
• Plant your (newly purchased!) veggies and herb plants when nighttime temperatures are consistently a minimum of 50 degrees, and make sure to protect them with cover when temps drop below 40 degrees. This includes tomatoes, peppers, and eggplants.
• Consider your planting location, i.e. Rotating your crops to prevent bacteria that might have infected plants last year from doing so again.
• Weeding is essential as much as possible, so let’s get on it!

Trees and Shrubs

• Just in case May ends up being sparse in the precipitation arena, don’t be afraid to bust out your hose and give your trees a good soaking, watering deeply once per week.
• This is also a good month to prune trees to remove any dead branches from needed but possibly damaging snowfall.
• Mulching is a great way of helping your tree retain water, just make sure to keep it between 3-4” deep and about 6” away from the trunks so it doesn’t hinder healthy root development and allows the plant to take up moisture.
• Prune summer blooming shrubs that bloom on new growth, such as roses before they begin to flower. Refrain from trimming shrubs that bloom on old growth such as lilacs until after they flower.
• This information sheet has great pruning information.

Lawn Care

• This is a great month to aerate the lawn to loosen up soil for better water absorption, as well as removing thatch (tight, brown, spongy, organic layer which can cause problems down the road in terms of lawn health) when it becomes too thick.
• After aerating is a wonderful time to overseed your lawn to regrow any bare spots which have developed over time.
• Watering is important for lawns as for other plants as this month heats up. Of course, if there’s rain or snow, hold off.
• Watering in the late evening or early morning helps retain more water as the weather tends to be cooler and more humid at these times.
• This is the month to treat your lawn for Japanese Beetle grubs. Use products like GrubGONE! which has been shown to do a great job of stopping this pest before it leaves your lawn and infests your plants.   

Perennial / Annual Flower Beds

• Continue cleaning out the garden, including spent flowers and cutting back foliage to help perennial plants direct their energy to growing.
• Look at possible locations where plants might not have performed as well as desired and where you can fill in or move existing plants.
• Waiting until late May to plant annuals will give them a chance to survive any crazy cold spells, although there are many that will do well in cool weather, such as petunias and pansies.
• This is also a great time to plant summer blooming bulbs!

May is such a great gardening month, let’s take advantage it and grow, grow, grow!

Visit the CSU Extension Yard and Garden website (https://extension.colostate.edu/topic-areas/yard-garden) for more gardening tips.

Colorado Gardening Calendar for April 2024

By: Molly Gaines, CSU Extension-Denver Master Gardener since 2019

Last week’s snow covering forsythia starting to bloom. Photo: Molly Gaines

Signs of spring are everywhere in Denver. Daffodils, crocus and other spring flowers in full bloom one day; covered in ice and snow the next. Oh, to be a gardener at 5,280 feet!

While it’s too early to spend a lot of time planting, it’s a perfect time to prepare your soil, garden beds, tools, pots and lawn for the 2024 growing season. Below are a few gardening activities to consider before Mother’s Day, May 12 (around the safe zone from hard frosts) for planting most plants, flowers and vegetables.

Crocus are always a welcome first sign of springtime. Photo: Molly Gaines

As you plan your garden, it’s worth noting that some of the Denver metro is in a new gardening zone. Last November, the USDA announced updates to its “Plant Hardiness Zone Map,” updating this go-to tool for gardeners for the first time since 2012. The new map, which can be found here, places parts of Denver in Zone 6a rather than 5b. Zone numbers reflect the average extreme minimum temperatures and help determine what plants will thrive in each zone.  Higher numbers equal incrementally warmer low temperatures. For background about how to use this map as a planting guide, visit this helpful article from the National Gardening Association’s learning library.    

New USDA Plant Hariness Zone Map now places parts of Denver in Zone 6A. Credit: USDA

Vegetable Garden

• Clear remaining debris. Pull emerging weeds.
• When the soil is dry, add a fresh 2-3-inch layer of compost to your beds. This supports soil health and plant vigor. Gently work compost into the top layer of your existing soil with your hands, a trowel or a cultivator. Let rest a few weeks before planting.
• Plant frost-tolerant spring plantings, such as peas, spinach, arugula, radishes, Swiss chard, etc.
• Start indoor seeds for warm-weather vegetables such as tomatoes, peppers, squash, melons, etc.
• Reference this Vegetable Planting Guide to plan what you will plant when.

Trees & Shrubs

• The snowpack is solid Colorado-wide this year, well above 100 percent. This includes Denver. That said, if this month is dry, be sure to water your trees and shrubs.
• Early this month, prune deciduous trees, conifers and summer-blooming shrubs.
• Later in April into mid-May, prune rose bushes. For details on exactly how, why and when to do this, visit here.  This is weather dependent so watch for low temperatures and delay if a cold snap is predicted.
• Remove broken branches from trees and clear dead leaves and decayed fruit from the base.
• If you’re looking to plant a new tree, consider the Park People’s annual fruit and yard tree sale that begins April 20. Trees range from $50 to $80, and sales support the Denver Digs program. More details can be found here.  

Lawn Care

• Prep your mower, sharpening the blade as necessary and conducting other maintenance. Lawn mower blades should be sharpened at least once per season.
• If you use a pre-emergent weed product, apply in early April. For more details about how to use, visit here.
• Fertilize as desired, reading labels for proper application. Keep in mind that fall is the most important time for lawn fertilization. Applying only in the spring can mean excessive top growth and shallow root systems.

Perennial Beds

• Cut back perennial plants if this wasn’t done last fall, leaving 3 inches of the plant above the soil.
• Similar to your vegetable garden, the soil in these beds will also benefit greatly from compost, with the exception of native plants which generally prefer unamended soil.
• Pull emerging weeds now. Stay on top of them from the start.
• Divide overgrown perennials such as chives, sedum, grasses, phlox, daisies, hosta, etc. This will lead to healthier plants and better growth.

Other April Gardening Thoughts

• Assess garden supplies. Purchase or plan to borrow anything needed. Sterilize and sharpen garden tools.
• Empty any pots or containers still holding last year’s dead plantings. Clean and disinfect them to prevent disease in new plantings.

These pots need to be cleared of last year’s plantings, disinfected and filled with new soil for plantings. Photo: Molly Gaines

• Denver Water recommends waiting to turn on your irrigation until after the last freeze, typically in early May. Hand water until then.
• Sow wildflower and pollinator seed mixes.
• Prepare for frost, hail and other bad weather. Have sheets of plastic, old bedsheets and five-gallon buckets in easy reach for late-season snow or spring and summer hail. Remember the hailstorm that hit Denver late June last season?

Sad peas in a bed covered with hail. June 29, 2023. Photo: Molly Gaines

Springtime in Denver is special. I love watching new life slowly unveil itself. It’s a time full of promise, new beginnings and high anticipation of the color, flavor and textures around the corner. The more prepared you are in April, the more enjoyable your summer gardening season will be.

As always, if you have questions about plants, planting and any other gardening and yard related topics, visit the CSU Extension Yard and Garden website for tips.

Colorado Gardening Calendar for March 2024

By: Valerie Podmore CSU Extension-Denver Master Gardener since 2020

Snowdrops popping up through the snow (photo by Pixabay)

Hey friends, remember when it was January, and we were all lamenting how it seemed to never end? And then February was unseasonably warm and short, but Punxsutawney Phil did tell us early spring!  Well, celebrations are in order because it’s MARCH!

This is one of the best months for watching new growth come up and reigniting that gardening bug. Of course, there are other, more “productive” tasks to perform as well, so mark your calendar to get these gardening to-do’s done in your yard and garden.

Vegetable Garden

Coming soon to a veggie garden near you! (photo by Pixabay)

So, my first attempt at veggie gardening was “fun,” but because I’m not super into cooking it may have stopped me from being more attentive to my sad plants. That’s ok, maybe I’ll stick to flowers instead. For those of you who are more dedicated than I, take a look at some tasks below and know that gardening in Colorado usually requires the fastest-growing, most weather-hardy vegetable varieties.

• Clean out debris and replenish soil in vegetable beds while we wait for our seeds to start.
• Starting seeds indoors in March is perfect for any vegetables that should be planted outdoors in early April. Here is a list of seed companies if you are thinking of starting your vegetables from scratch.
• This link from The Old Farmer’s Almanac has all the recommended indoor and outdoor planting dates for vegetables and herbs.
• Think about layouts for your raised beds (if that’s what you’re using). This pdf has a lot of helpful information.
• Since spring seems to be coming early, vegetable garden water conservation might be a good topic to study.

Trees and Shrubs

Early spring Forsythia bloom (photo by Pixabay)

• Late winter/early spring are ideal times to trim trees, as explained on this page by the Colorado Forest Service.
• Precipitation in late 2023 was sparse, so it’s always a good idea to remember good watering habits for our trees and shrubs.
• This interesting article explains tree root systems and how our soil health, moisture and compaction (or not) can affect these very important plants.

Lawn Care

To lawn or not to lawn is becoming a much-discussed subject, given higher temperatures and lower precipitation amounts. Historically, many homes have yards planted with Kentucky Blue Grass lawns, which need more water, mowing and fertilization. This might be a good time to consider replacing your lawn with more native grasses (if you want to keep a lawn) or other native plants.

• In conjunction with Denver and other counties’ water providers, Resource Central has a lawn removal program to assist with moving to more natives.
• This is a great article about what native lawns can be planted instead of that water-hungry bluegrass.
• For those who want to keep their lawns as is (no judgement here!), mid- to late-March is a great time for aerating and general tidying.

Perennial Flower Beds

When I first became interested in gardening, I was – like all of us, I’m sure ­– in love with plants that were different looking, showy, flowering and easy to grow in places like Alabama, but not Colorado. I’m finally learning my lesson that it really is about the principle of right plant, right place. In addition, having listened to and read books and articles about the benefits of planting natives in our landscapes, I am becoming more attentive to what plants I choose for my landscape. I look not only for beauty, but regeneration and restoration. I mean who wouldn’t want to be part of a national movement like Homegrown National Park?

• Since I’m on my native plant kick, here’s a plug for these Colorado native perennials that can really enhance our landscapes and make them more sustainable.
• This is also a great month to start clearing out old, dead growth – as long as the weather is warm enough – to make room for shoots popping out of the ground.
• This page gives great information on perennial gardening so you can have everything prepped when you’re ready to put actual plants in the ground.

Annual Flower Beds

• Even though you can plant annuals pretty much anytime, they MOSTLY like being planted after last frost (usually around May 10-15).
• This is a great time to look at cool-weather annuals like pansies.
• The annual CSU Flower Trials have tested and found flowers that are hardiest and grow best through the tough, Colorado life. Check it out!

Make sure to mark your calendar for the May Denver Master Gardener plant sale (May 18 & 19) and visit the CSU Extension Yard and Garden website (https://extension.colostate.edu/topic-areas/yard-garden) for more gardening tips.

Colorado Gardening Calendar for May 2023

By: Valerie Podmore, CSU Extension – Denver Master Gardener since 2020

May is finally here (or What? Already? Depending on your point of view). Now we can get down to the real business of planting. While Denver’s last frost generally falls between May 5^th and 15^th, we know the weather can change at any minute (remember last year’s snow on the 21^st?), we can make progress on many gardening tasks to keep us happy.

First, mark your calendar to make sure you don’t miss the Denver Master Gardener Plant Sale on May 20^th and 21^st at Harvard Gulch Park. We think it’s the best plant sale around!

Next, look at the information below to make sure you have garden success this month.

Vegetable and Herb Garden

This is something I’m attempting more of this year and am excited that the time has come to begin. Having said that, I KNOW it’s important to pay attention to temperatures, light and water needs of veggies and herbs so will be reading up as much as possible to have success. Wish me luck!

Here’s some solid advice.

• Now is the time to plant colder weather veggies and herbs. These include lettuces, spinach, peas, broccoli, cabbage, among others. This article gives great information on cool season veggies.
• Wait till later in the month, when the soil has warmed up and evening temperatures are consistently above 50 degrees, to plant warm season veggies such as tomatoes. Same for everyone’s favorite herb, basil. Learn more here.
• Before planting in the garden, be sure to harden off, or acclimate transplants to outdoor temperatures to help them establish. Find tips here.
• If you are wanting to plant herbs look at this AWESOME pdf with so much information.
• This page gives information on every veggie and herb related subject you could want! Beware of analysis paralysis (my “toxic trait”) as you slide down the rabbit hole of content.

Crabtree blossoms by Miranda Podmore

Trees and Shrubs

• With all the wonderful moisture we had earlier this winter, it’s tempting to think that Mother Nature will take care of our trees, but this is the time to watch and if necessary, water deeply once per week.
• Look at pruning shrubs and trees to maintain their shape and remove any winter kill. Prune early season bloomers such as forsythia and lilac shortly after blooming as they flower on last season’s growth. Use this guide to help you.
• Last week’s post about five trees to consider planting contains useful information on selections you might add to your landscape this month.
• Probably everything you ever wanted to know about trees and shrubs is right here!

Lawn Care

• I thought I’d seen all there was to know about lawns (well not really, but still…there’s a lot of information out there on the world wide web!), but here’s a great all-in-one information source for selection, care, replacement and general best practices for Colorado lawns.
• Perhaps waiting a bit to mow will allow pollinators who utilize the flowering plants in our lawns (dandelion, clover) to have just a bit more food.
• Consider converting your turf to more water-wise options. It’s a worthwhile proposition.  Here’s a great guide to help get started.

Perennial Flower Beds

• Get ready as the time to plant your perennials is nigh! The old adage of waiting until Mother’s Day may or may not be quite accurate but this month is definitely the time when we can fill in spaces in our landscape with plants which will return again and again.
• This is a great guide on how to prepare the planting site and how best to plant for success.
• If you are looking to attract more pollinators, this is an excellent guide to selecting plants.

Annual Flower Beds

• Annuals can provide so much needed color after a drab, cold winter and there are many which are cold hardy that can go in the ground early this month. Take a look at this information sheet.
• CSU conducts flower trials every year which showcase the best performers over a three-year period. Use it to make your choices for both annual and perennial plants.

May is certainly a great month to catch the gardening bug (no pun intended), get back to enjoying the warm weather, and get our hands in the soil!

Visit the CSU Extension Yard and Garden website (https://extension.colostate.edu/topic-areas/yard-garden) for more Colorado gardening tips.

Five Trees to Consider Planting This Spring

By Lois Margolin, CSU Extension – Denver Master Gardener since 2011

Spring is the ideal time to plant trees in Denver because the cooler temperatures help the plant’s root system establish before summer’s heat arrives. By fall, the tree will have acclimated to its new home and with proper care, be prepared for winter.

Catalpa trees are successfully grown along the Front Range. Their whimsical string-bean-like seed pods & heart shaped leaves make them easy to identify. Image: Pixnio.com

Planting a variety of species creates a diversified tree canopy which supports a healthy ecosystem. It ensures that if/when a species-specific pest, such as Emerald Ash Borer (EAB), gains a foothold, the tree canopy will suffer less impact.

Colorado State University (CSU) offers research-based information to help select trees that are ideal for our unpredictable, challenging climate. Of note is The Front Range Tree Recommendation List developed by Colorado State University, the American Society of Landscape Architects, the Colorado Nursery and Greenhouse Association, and the Colorado Tree Coalition. It includes a rating scale for many trees including confers, fruit-bearing, and shade trees.

The list also describes trees that are ill-advised, such as aspens which no longer thrive in the front range due to our increasingly hot summers, and ash trees due to the expected arrival of EAB. Consider downloading it on your phone so you can consult it when tree shopping.

Tree Recommendations

The following trees do well in the Front Range and are some of my personal favorites. You may want to consider one or more for your landscape, keeping in mind the size of the tree at maturity, its moisture needs, and your environmental conditions.

Ohio Buckeye (Aesculus glabra). This well-rounded tree grows approximately 35’X20’ with lovely cream-colored spring flowers and red-orange-yellow fall foliage. It’s best planted in a protected area as high winds and hail can damage the leaves but won’t harm the overall health of the tree. Find additional information on this tree here.

I like to collect the nut-like seedpods or “buckeyes” in the late summer and use them for craft projects with kids. They make cute necklaces by drilling holes into the nuts and stringing them together.

Ohio Buckeye foliage James St. John, CC BY 2.0 , via Wikimedia Commons

Buckeyes H. Zell, CC BY-SA 3.0 , via Wikimedia Commons

Catalpa (Catalpa spp). The Front Range Tree Recommendation List gives catalpa trees the highest rating. Give it lots of room as it can reach 30′ wide and 70′ tall. Starting in late May, white flowers emerge, followed by long, string-bean-like inedible seed pods. Foliage is large, showy, and heart-shaped. Find more about Catalpa speciosa here.

Showy Catalpa blossom
Ввласенко, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Kentucky Coffee Tree (Gymnocladus dioicus) is another highly recommended large tree (50’X40’). It’s an excellent shade tree that prefers low-water conditions once established. Despite its name, the seeds and pods are poisonous. Find more about this tree here.

Kentucky Coffee Tree
Credit: SEWilco, CC BY-SA 3.0 , via Wikimedia Commons

Japanese Tree Lilac (Syringa reticulata) is my all-time favorite small tree (about 30′ x 25′ at maturity). In late May it explodes with fragrant, cream-colored lilacs blooms at the tips of its branches. Absolutely a beautiful sight to behold from an upstairs window! Find additional information on this tree here.

Japanese Lilac Tree TheKohser – Gregory Kohs, CC BY-SA 3.0, via Wikimedia Commons

Serviceberry (Amelanchier spp.) is a small tree that produces early summer flowers followed by edible fruit. The berries of Saskatoon (Amelanchier alnifolia) are notable for their blueberry-ish flavor. Serviceberry trees can be single or multi-stemmed depending on the cultivar selected. Learn more about serviceberry trees here.

Serviceberry inflorescence Image: Pixabay.com

Final Thoughts and Resources

• Do your homework before selecting a tree. Be sure to consult the Front Range Tree Recommendation List for information about disease and insect-prone species, moisture requirements, dimensions, and winter care, and use additional research-based information for our area to make an educated decision.
• Proper planting is critical to a tree’s survival. CSU’s Garden Notes #636 is an excellent instructional guide to planting and caring for new trees. Review it before starting to dig!
• Water is essential. In addition to carefully watering your new tree in spring and summer, it is also absolutely crucial that you water in the winter, especially for the first three years. Find directions for watering newly planted trees here and winter watering instructions here.
• Native trees are important in Colorado landscapes. This CSU publication and the Colorado Native Plant Society’s website are valuable resources to help you learn more.

Low-Water Vegetable Gardening in Colorado

By Felicia Brower, CSU Extension – Denver Master Gardener since 2020

Water and vegetables go hand-in-hand. The more water you give to your growing vegetables, the bigger and better tasting the harvests tend to be. As water restrictions become common and conserving water becomes more important than ever, it’s going to be crucial for gardeners in Colorado to figure out how to resourcefully use water if they want to keep growing fresh vegetables.

There are a few key ways to cut back on water in the garden. Simple things like choosing vegetables that can survive (and even thrive) using less water, maximizing the water that you do use, and preventing water loss are all ways to keep your garden looking great without relying on excess water.

Chives are always the first thing to pop up in spring without any supplemental water. Photo by Felicia Brower

When it comes to choosing what to grow in your garden, it’s important to remember that different vegetables require different amounts of water. Vine crops need less water (and actually tend to be overwatered in the home garden), while beans and sweet corn typically need more water than other types of vegetables. Many perennial herbs don’t require a lot (if any) supplemental watering to do well. My parsley, chives, sage, thyme, and lemon balm are the first things to show up every year in my garden without any extra water to help them grow.

Not only do vegetables have different water needs, but some also need more water during certain parts of their life cycles. For example, peas need more water during their pod filling period while tomatoes need more water during flowering and fruiting. 

It’s also important to choose regionally-adapted vegetables. Vegetables that are selectively bred to excel in areas where drought is common are more likely to have fewer issues when they’re watered less in the home landscape. Search online for Colorado seed companies and choose vegetable varieties that are drought tolerant. While beans can often be huge water users in the garden, varieties like Zuni Gold, Paiute Gold tepary, and Sonoran White tepary are drought-tolerant and grow well without needing huge amounts of water. In fact, during some of my drier years, they stayed greener and kept producing while their neighbors wilted and struggled. 

Zuni Gold beans, a southwest Pueblo variety, are highly adaptable and drought tolerant, making them a favorite in my home garden.
Photo by Felicia Brower.

One of the best ways to conserve water is to maximize water efficiency. If possible, install in-ground drip irrigation or use cost-effective soaker hoses so that your water reaches the roots of the plants instead of being wasted on foliage or in spots without anything growing. Water at soil level near the roots in the morning, avoiding the heat of the day, to reduce the amount of water lost to evaporation and to avoid issues like powdery mildew on the leaves of your plants. 

Here are a few additional ways to grow a low-water vegetable garden: 

• Different soil types have different water needs, so water according to your specific soil type. Loamy soil needs deep, infrequent watering instead of regular, light daily watering while sandy soils need more frequent, less deep watering because they lose water faster than clay soils. 
• If you use overhead watering, don’t water your plants on very windy days. The wind will blow your water away and prevent it from reaching the roots. 
• Before you do any watering, test your soil’s moisture level. The surface of the soil might be dry but the roots might not be.
• Your garden layout can also impact how much and often you have to water your garden. Narrow rows need more water, so grow your veggies in beds, grids, or wide rows. 
• As with any plants in your home landscape, plant vegetables with similar water needs together. If you have a mix of drought tolerant plants and high-water plants, make sure they’re kept separate so you don’t overwater or underwater, both of which cause stress and can impact the quality of your harvest.
• Use mulch (green or otherwise) to keep moisture in the soil. You won’t have to water as much if you grow intensely (close together) or use another organic mulch to slow down evaporation. 
• Grow during Colorado’s shoulder seasons to take advantage of moisture from snow and spring rains and cooler temperatures, so there’s less water loss due to heat.
• Before you plant anything, take time to amend and prep your soil. Healthy soil retains water and is full of nutrients that prevent you from overwatering to try and make your plants stronger. 

As water conservation becomes more important in the west, it’s crucial to find ways to use less, especially for things like growing food. Follow CSU’s Colorado Vegetable Guide and the “Water Conservation in the Vegetable Garden” GardenNotes chapter for advice on best low-water vegetable gardening practices. 

Colorado Gardening Calendar for April 2023

By Molly Gaines, CSU Extension – Denver Master Gardener since 2019

A reminder to resist the urge to plant frost-sensitive flowers and veggies this month. Ice encapsulates this blooming tree in mid-April.

As the saying goes, “April showers bring May flowers.” But in Denver, where one day the snow flies and the next day is sunny and 70, April is mostly a planning and prep month here. It’s a hopeful and exciting month for gardeners, filled with possibilities and dreams that this year, “I’m finally going to [fill in the blank] in my garden.” For me, it’s that I’ll finally install drip irrigation vs. hand-watering my vegetables and flowers. For you, it may be planting trees for some much-needed shade or creating your first vegetable garden. Whatever your goals, following is a guide to help keep your April gardening tasks on track.

Vegetable Garden

• Clear debris from last year’s garden and any winter mulch covering the bed, such as dead leaves. Pull any emerging weeds, which are easier to deal with early in the season.
• When the soil is dry, not wet, or muddy, add a fresh 2-3-inch layer of compost to your beds. This will greatly support soil health and the vigor of your plantings. Gently work compost into the top layer of your existing soil with your hands, a trowel or a cultivator. Let rest a few weeks before any planting begins.
• Plant frost-tolerant spring plantings, such as peas, spinach, arugula, radishes, Swiss chard, etc. You may wish to soak your pea seeds in warm water prior to planting for faster germination. 
• If you haven’t yet started indoor seeds for warm-weather vegetables such as tomatoes, peppers, squash, melons, etc., now is the time. 
• Reference this Vegetable Planting Guide to plan for what you will plant when. 

Trees and Shrubs

• Continue hand-watering your trees and shrubs, particularly if it is a dry April.
• Early this month, prune deciduous trees and shrubs. 
• Remove broken branches from trees. Clear away dead leaves and decayed fruit from the base, as they can house unwanted inspects and pathogens. 
• I’ve sadly been noticing a lot of tree removal in my neighborhood lately. Denver needs a more robust, healthy tree canopy. This is a great month for planting new trees, selecting varieties that best suit Denver’s climate. Here is a guide to successful tree planting. If you’re in the market for a tree, check out the Park People’s annual tree sale on April 22, which supports the Denver Digs Trees program.

Lawn Care

• Prep your mower, sharpening the blade as necessary and conducting any other necessary maintenance. 
• If you use a pre-emergent weed product, apply before weed seedlings – particularly crabgrass – sprout. Targeted weeds can vary by product.
• Fertilize as desired, reading labels for proper application.
• Denver Water recommends waiting to turn on your irrigation until after the last freeze, typically in early May.

Perennial Beds

• Cut back perennial plants if this wasn’t done last fall, leaving 3 inches of the plant above the soil.
• Plant asparagus, rhubarb, berries, bare-root roses. Soak any bare-rooted plantings for a few hours prior to planting.
• Pull emerging weeds now, staying on top of them early in the season.
• Divide perennials that are overgrown, such as chives, sedum, grasses, phlox, daisies, hosta, etc. This will lead to healthier plants and better growth. It will also allow you to give away new, inexpensive perennial plantings to your neighbors and friends. 

Other Thoughts for April Gardening

• Inventory and prep garden supplies. Sterilize and sharpen garden tools. 
• Sow wildflower and pollinator seed mixes.
• Consider and plan for any trellising that may eventually be needed for your vegetable and perennial gardens.
• Be prepared for frosts and bad weather. Have sheets of plastic and old bedsheets nearby your garden for quick tarping in case of late-season snow or hail.

I hope this list makes tracking all of the April garden to-do’s a bit simpler. And remember this about April: attentiveness and proper planning for your landscape and gardens now means less work and hassle, and more ease and enjoyment, as your summer gardening season progresses.

Organizing and assessing  tools and supplies needed for the gardening season.

Planning a Garden for Thrills Spring to Fall

By Terry Deem-Reilly, CSU Extension – Denver County Master Gardener since 2003

One of the most satisfying aspects of gardening is seeing dormant sticks, clumps, and bulbs that were placed so hopefully in the soil leaf, blossom, and fruit. At the same time, one of the most daunting aspects of gardening is ensuring that all of that leafing, blossoming, and fruiting doesn’t occur all at one time. A garden that ceases to bloom after the last tulip has disappeared or browns up from the fall equinox until the following spring won’t satisfy the senses nearly as much as one that displays continuous interest. Moreover, landscapes which produce pollen and nectar throughout the season provide important nourishment for pollinators.

Hellebores kick off the season. Pixabay.com

Other posts in this blog have stressed the necessity of matching plants to sites, soil, and sun exposure that will allow them to flourish. Horticultural considerations don’t disappear when the goal is season-long color and interest; selecting plants that like the same conditions and grouping them into the areas where they’re most likely to flourish are indispensable to having the three-season garden of your dreams.

The detailed first steps to success with any perennial garden can’t be adequately covered here but are well-explained in the Extension fact sheet Perennial Gardening. Remember the conditions in your site when reviewing plant lists.

Next, consider whether you’d like to include non-native or xeric/native trees, perennials, and shrubs; this decision will determine the amount of time and attention (not to mention water) you’re going to devote to a three-season garden. Xeric plants and Western natives won’t need much maintenance after the first season or two, but a lush English-style bed of roses, delphiniums, and pinks demands careful soil amendment and regular irrigation, mulching, and fertilization. Decide what look you’re after and what it will take to achieve it.

Mid-summer morning & the garden’s in full bloom. Photo: Linda McDonnell

To make plant selection a little easier, here are suggestions from plant lists showing seasonal bloom by non-xeric and xeric/native varieties, with links to the complete lists for easy reference.

Nonxeric or Non-Native Perennials

• Spring: early blooming bulbs, primrose, candytuft, viola, creeping phlox, hellebore, peony, geranium
• Summer: garden phlox, dianthus, lily, verbascum, hosta, campanula
• Fall: aster, chrysanthemum, Japanese anemone, lobelia

For the complete list, see the Plan Your Garden with our Perennial Flowering Plants by Season Guide. Some of the plants shown above also appear in 25 Perennial Flowers That Bloom From Spring To Fall. Timberline Landscaping in Colorado Springs has published a bloom calendar of perennials that do well on the Front Range.

Xeric and/or Native Perennials

• Spring: early blooming bulbs, columbine, amsonia, windflower, pasque flower
• Summer: chocolate flower, poppy mallow, asclepias, eriogonum, penstemon, oenothera
• Fall: helianthus, asclepias, winecups, hyssop, agastache

These plants, and many others, can be found in these Extension fact sheets: Native Herbaceous Perennials for Colorado Landscapes and Xeriscaping: Perennials and Annual Flowers. These resources also indicate water needs, light requirements, and plant heights and descriptions.

Want to see more native plants? CSU’s Low-Water Native Plants for Colorado Gardens: Front Range & Foothills includes not only common and botanical names; height; color, size, water and sun requirements; and wildlife value, but also design plans and photos of great local native gardens. Mountain residents will find the Extension fact sheet  Flowers for Mountain Communities useful for plant selection and advice on cultivation.

Shrubs and Trees

Hawthorn tree in fall. Pixabay.com

Our guide wouldn’t be complete without recommendations for suitable trees and shrubs to supplement your perennial display. Many plants in these categories offer blossoms, fruits, and/or color that add interest throughout the season; a number of them offer all three!

Here are examples of shrubs that add color and interest through the seasons:

• Serviceberry
• Fremont mahonia
• American plum
• Buffaloberry
• Western sand cherry

For a complete list, consult the Extension fact sheet Native Shrubs for Colorado Landscapes. Again, you’ll see botanical and common names, size, and sun, moisture, and sun requirements for each shrub.

Some trees that add interest include:

• European mountain ash
• Pine
• Colorado blue spruce
• Aspen (Foothills and submontane areas only!)
• Maple

See the fact sheet Native Trees for Colorado Landscapes and the CSU publication Recommended Trees for Colorado Front Range Communities for more details. Mountain gardeners should consult the fact sheet Trees and Shrubs for Mountain Areas for suggestions.

Finally, don’t discount the value of roses when planning for season-long color. Even with the plague of the Japanese beetle, roses (especially hip-bearing and species roses) dependably add color through the growing season. The Denver Rose Society publishes a list of the best roses for our climate: Recommended Roses for Colorado.

If problems arise, always, ALWAYS rely on research-based information to answer your questions;  Denver Extension stands ready to help!

Tips for Beginner Colorado Gardeners

By Terry Deem-Reilly, CSU Extension-Denver Master Gardener since 2003 

Congratulations! You’ve decided to plunge into gardening, which will improve your diet, health, property values, and mental equilibrium. Before wielding that spade and acquiring your plants, however, you’ll want to consider some facts about Colorado gardening that will ensure a productive and stress-free (well, mostly stress-free) first year. 

Firstly, Colorado is an unusual place to grow a garden. It’s at once one of the easiest and one of the most challenging locations to cultivate plants. Knowing a few facts about our growing conditions and planning to how to cope with them are the first steps in a happy garden experience. Here are the basics about our growing conditions: 

• The average elevation of locations in Colorado is 6800 feet above sea level. 
• High elevation equals intense sun and low humidity. 
• Colorado experiences drastic temperature swings, sometimes within the same day. 
• Soil is characterized by high pH and clay texture, so tilth (ability of the soil to support plant life) is poor, namely: 
  • A high concentration of calcium carbonate in our soil raises pH (ratio of acidity to alkalinity) above the neutral level of 6.0-7.0; and 
  • Clay soil contains small pore spaces, making drainage slow and limiting root growth and oxygen content. 
• Untimely, damaging snows occur in the spring and fall (remember the snow just before Memorial Day last year?). 
• Our growing season begins about May 15^th and ends around October 15^th – that’s only five months between the last frost of winter and the first frost of fall. This makes vegetable gardening particularly daunting. 

For a more detailed discussion of Colorado gardening challenges, consult the Extension Fact Sheet Colorado Gardening: Challenge to Newcomers (natives will like it, too!). 

Secondly, employing these strategies will minimize the difficulties and maximize the results in your first Colorado garden: 

• Test the soil. The CSU Soil, Water, and Plant Testing Laboratory has (yay!) reopened. Click on the link for information on preparing and submitting samples and get yours in early – the lab gets a lot of business. Results include recommendations for soil management and fertilization. 
• Amend your soil as needed. The correct amendments will add organic matter, improve aeration and water infiltration, and encourage the growth of useful organisms like bacteria, fungi, and earthworms. Use caution with manure-based composts that may be high in salt, wood chips that consume nitrogen while decomposing, and biosolids that contain pathogens and chemicals. For more details on selecting and using soil amendments, consult the Extension Fact Sheet Choosing a Soil Amendment. Bear in mind that minerals like iron and nitrogen are inaccessible to plants in our soil and must be added in formulations that the roots can absorb. 
• Apply the principle “right plant, right place” by selecting plants appropriate for our region and siting them in the proper soil and sun/wind exposures. Consider the plants’ requirements when shopping – check plant tags and catalog descriptions before making your purchases. And remember to group plants with similar needs in the same area of the garden; avoid placing roses that need regular irrigation and fertilization among native grasses that will perform nicely without either. 
• The advice given by clerks at Home Improvement Megastore notwithstanding, we CANNOT change the pH of our soil. If you’re really dying to have a holly, blueberry, or other acid-loving plant in your garden, consider growing a dwarf variety in a large container with a soil composed of planter’s mix and peat moss. (Container plants require protection or a move into the garage in winter temperatures.)  
• Mulch, mulch, mulch nonxeric plants to a depth of about two inches – this includes vegetables! 
• Water appropriately. Newly planted trees, shrubs, and perennials, including xeric varieties, require correct watering in their first summer and winter watering in dry periods. Vegetables need water at least once a day in hot weather, often twice a day if they’re grown in containers. Consult this PlantTalk Colorado™ script for some irrigation tips for trees and shrubs. 
• Use season extenders like hot caps, row covers, and cold frames to lengthen our short growing season at both ends. 
• Learn which vegetables are cool season (greens, chard) and warm season (tomatoes, peppers) and when to plant both. 
• When caught in a quandary, always, ALWAYS rely on research-based information to answer your questions; these resources are your source for science-based solutions to garden problems: 

Ask Extension (Colorado) 

https://ask2.extension.org/widget.html?team_id=1955?default_location=CO?default_county=All

Colorado State University Extension (posts and fact sheets) 

https://extension.colostate.edu/topic-areas/yard-garden

Gardening Help at Denver Botanic Gardens  

gardeninghelp@botanicgardens.org or 720-865-3575 

Colorado Gardening Calendar for March 2023

By Valerie Podmore, CSU Extension-Denver Master Gardener since 2020

These Tulips have restored my faith in spring and gardening! by Valerie Podmore

I have a confession to make. I have not been thinking about the garden much this past winter and almost thought (dare I say it) I might just pack the whole thing in. However, my eye was caught this morning by the sight of tulips starting to pop through the soil and it made me happy, and I think I have caught the bug again! So, let’s see what we can do now that we are starting to see more sunshine, and the days are getting longer. MARCH is one of the best months to prepare for the upcoming growing season, so mark your calendar to get these gardening to-do’s done in your yard and garden.

Vegetable Garden

This year I am determined to try raised bed gardening and am beginning to research what it takes to succeed. Maybe we can learn together!

• I’m starting with this article to help me figure out what to plant as a new veggie gardener.
• The raised bed method of gardening is explained in depth here. I must work to not get overwhelmed by the wealth of knowledge!
• If you are like me and have delusions of veggie growing grandeur, you will possibly have more seeds than any normal human should be allowed to have! Many of these are probably no longer viable, so best to inventory your seeds and order any you might still need.
• Last week’s post about seed starting is a timely and great way to educate ourselves on starting our plants using the DIY method.

Trees and Shrubs

• Since we’ve had so much snowfall (we’ve certainly needed the moisture!), supplemental watering is possibly not needed, but anything can happen in March so remember to water your trees and shrubs if there’s a drop-off in precipitation.
• This is a great month to prune trees and shrubs for those who want to get outdoors and “DO SOMETHING!”

Lawn Care

• If you love late winter/early spring lawn and garden care (who doesn’t love a good spring clean?) there are great suggestions in this article.
• Early March is a great time to sharpen up your mower blades and add or replace oil, clean shovels and pots, and generally tidy up anything that has been languishing in wait for warmer days.
• Late March is a great time to start aerating as long as the ground is not frozen.

Perennial/Annual Flower Beds

• While most of our garden isn’t completely awake yet, we can still take stock of what plants worked last year and what we’d like to fill in this year.
• That brings us to seeds and bulbs! See what bulbs you’ve got that can be replanted from storage; what seeds can be sprouted indoors.
• If you attended the Colorado Home and Garden Show last month (probably good that I didn’t, as I would become way too over-ambitious!), use any ideas you gained for changes you want to make.

Don’t forget to visit the CSU Extension Yard and Garden website (https://extension.colostate.edu/topic-areas/yard-garden) for more gardening tips, and yay spring!