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 February 2024

By Margerie Hicks, CSU Extension – Denver Master Gardener since 2010

Blue fescue grass poking through snow at Denver Botanic Gardens. Photo: Margerie Hicks

February is one of the best months to enjoy the interesting patterns, textures, and shapes that dried grasses and perennials form in contrast to the snow. It is also a time to read or otherwise educate yourself about gardening trends and ideas. And finally, it is a time to complete the few but important tasks needed in February to prepare for the coming growing season.

Winter Interest

Autumn joy sedum keeps its color and form. Photo: Margerie Hicks

If you refrained in the fall from cutting down ornamental grasses, perennials with balls of seeds like echinacea, or plants that keep their color and form, you now have interesting winter patterns and shapes to enjoy. You have also helped provide shelter and food for wildlife, such as birds and insects.

If you don’t already have any sedum Angelina, make a note to plant some in the spring to enjoy next winter. It is a ground cover that is light green in the spring, yellow in the summer, and orange with green accents in the winter. It provides a wonderful splash of color in the winterscape.

Sedum Angelina adds multi-season beauty. Photos: David J. Stang, CC BY-SA 4.0 via Wikimedia Commons

Gardening Edification

• Expo: The annual Colorado Home and Garden Show runs from February 24^thto March 3^rd. Master Gardeners will be on hand to answer gardening questions at the large CSU Extension display. Be sure to stop by and say hi.
• Books: You may have some gardening-related books waiting to read on a cold winter night, but in case you want suggestions check out our earlier post,  Winter Reading for Gardeners.
• Websites: CSU Extension’s website offers research-based fact sheets and videos on a wide range of gardening topics. Additionally, the internet is filled with gardening information and pictures. The most reliable sources have an “.edu” extension on the address, indicating an affiliation with university horticulture/agriculture research.
• Gardening classes:  Local garden shops and the Denver Botanic Gardens offer classes on many topics that may pique your interest. You can also find a wide array of webinars offered by CSU Extension here.
• Take our reader survey:  We’d love your feedback and ideas for future posts. Find the survey here. Survey closes February 18^th.

February Tasks

Deep watering tool. Photo: Margerie Hicks

There are a few tasks that should be done and many that could be done this month. A good overview can be found in this Late Winter Garden and Lawn Care fact sheet. Key tips include:

• Water:  All trees, shrubs, and perennials will benefit from regular winter watering, especially those that are less than two years old. Water once a month on days when the temperature is 40 degrees or warmer with no snow cover. Click here for a fall and winter watering fact sheet that will make your efforts most effective.
• Mulch:  Woody plants benefit from mulch to preserve soil moisture. Rock or gravel mulch is useful in retaining heat. Apply as needed.
• Prune:  This is a good time to prune broken and unwanted branches from trees and shrubs, especially fruit trees.

Enjoy your gardening leisure in February. May will be here soon enough.

Speaking of May don’t forget to mark your calendars for our amazing plant sale!

Colorado Gardening Calendar for January 2024

Early January at the Denver Botanic Gardens Photo: Linda McDonnell

By Linda McDonnell, CSU Extension – Denver Master Gardener since 2013

It may be tempting to kick back and think there is nothing much to do in the garden this month. And while it is not the busiest time, taking a few steps when needed will set plants, trees, and lawns up for future success.

Winter Watering – January’s Most Important Task

It’s important to water trees, shrubs, perennials, and lawns during extended dry periods of 2-4 weeks. Supplemental water provides root systems with moisture that is critical to long-term plant health. It is especially crucial for new plants (1 year old or less) with smaller, less developed roots. Without this added moisture, plants may exhibit stunted growth, be more susceptible to disease, or die. Often decline is not noticeable till next summer when the root system can’t support the plant’s vigorous growth.

Water early in the day when temperatures are above forty degrees. Give plants a good soak – 8 to 12″ deep and out to the drip line of trees. Find more information on winter watering here.

Branches of  ‘Carol Mackie’ Daphne will easily split under heavy snow. Photo: Linda McDonnell

Trees and Shrubs

Heavy snow can crush or bend the limbs of trees and shrubs. Remove it by lifting branches lightly from the bottom with a broom to avoid breaking limbs. The branches will spring back as if to say thanks.

Prune any storm-damaged limbs as needed to prevent further breakage. Find additional post-storm tips here.

Perennials

Watch for signs of heaving such as cracked soil and raised crowns. This can happen around newly planted perennials when temperatures fluctuate widely. Heaving can expose and damage roots and kill plants. If heaving is present, check moisture, add soil or compost around the plant, and top with mulch.

Speaking of mulch – spread more where needed; it will help moderate temperature extremes.

Remove any diseased foliage that’s lingering in your beds to reduce the chance of infesting next season’s growth. Discard the foliage in the city’s green compost bin or trash. Home compost systems don’t get “hot” enough to destroy pathogens.

Plan Ahead

Should you keep or toss old seed packets? Learn how to tell here.

Scour online and print catalogs to find tried-and-true plant varieties along with new, buzz-worthy introductions.

The CSU Soil Testing Lab opens on January 21^st. If the ground is workable, consider beating the spring rush and sending a sample for analysis this winter. Find directions for digging the sample, using the results and costs here.

Check out the line-up of CSU’s no-cost webinars. There are lots of topics to choose from including turf alternatives, CSU test garden results, and water-saving tips. Find the full spring schedule and recordings of past webinars here.

Explore CSU’s resources for research-based gardening information that will make this year’s garden the best one yet.

Colorado Gardening Calendar for December 2023

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

Grasses left uncut provide great visual appeal throughout the winter months. Photo: Molly Gaines

A few snowfalls have already blanketed Denver, making old man winter feel official. This, and the fact that the holiday season is upon us, probably means garden to-dos are not top-of-mind for you. Yet, there are still some important tasks to consider, along with a handful of indoor activities, as we head into these darker days and colder months.

December’s Checklist 

Trees, Shrubs and Perennials 

• When there is no snow cover to provide trees, shrubs and perennials moisture, it’s imperative to their short- and long-term health to water them one to two times monthly. Here’s a great fact sheet from CSU with helpful guidelines for fall and winter watering.
• If you haven’t wrapped the tree trunks of newly planted trees, don’t forget this critical task. They need it for the first few years, until their bark develops texture. For more on this, visit this helpful article from North Dakota State University’s extension office. 
• When the snow falls heavily, shake snow from bent tree limbs and branches. This will avoid breakage. As needed, lightly prune broken limbs to avoid further damage.
• Add mulch to spots where it’s thin in your garden beds. This will help plants retain moisture and protect them from harsh winter winds and freeze/thaw cycles.

Sunflower still standing. Photo: Molly Gaines

Compost

• Yard waste, such as broken branches, and other remaining garden debris can be placed into your city compost bin. If you have a backyard compost bin or pile, continue adding brown and green materials, breaking larger debris into smaller pieces. These items will continue decomposing in the winter months, albeit at a slower pace. In Colorado, it’s best not to turn compost after December, according to this PlantTalk Colorado fact sheet on composting. Turning allows valuable heat to escape, and may stop processing in cold weather. To restart active processing, turn and mix in fresh materials with the winter compost. 

House Plants 

• Winter is the dormant season for non-blooming indoor plants. Reduce watering, stop fertilizing, and keep them away from drafts for the next few months.
• Increase humidity around your plants. Ignore misting with a spray bottle; for this to be effective, you’d need to mist for hours on end. Instead, group plants together on a pebble-lined tray and add water to just below the top of the pebbles.
• Check plants regularly for pests such as mealy bugs and spider mites. If present, treat and quarantine the infected plant. Find remedies here.  

Amaryllis adds a festive flair in December into late January. This trio should produce showy red blooms. Photo: Molly Gaines

Paperwhites take 4-6 weeks to bloom. Start them now for blooms in the new year. Photo: Molly Gaines

Speaking of house plants, ’tis the season for live Christmas trees and holiday plants. Here are some links to keep all of these at their best: Keeping the Ho Ho Ho in Holiday Plants, Tips for Caring for Your Christmas Tree, A Year in the Life of an Amaryllis, and Christmas Cactus Care. 

Holiday plants you may wish to consider for your home, or as a gift to others, include Christmas cactus, poinsettias, amaryllis or even paper whites. I’ve made it a tradition to send my mom a set of amaryllis (pictured above) each December so she can watch it grow through the holidays. Christmas cactus, which can be passed down for many years, can live to be 100 years old! They bloom in the winter and despite being cacti, need regular watering. Poinsettias add a beautiful pop of red, white or pink during the holidays and beyond. Their large size can make them a dramatic focal point of a room. 

Thank you for reading our blog. We’ll be back with one more post in December before wrapping up 2023. In the meantime, we wish you a beautiful, joyous start to your holiday season!

 As always, CSU is available in every season with gardening advice at the CSU Extension Yard and Garden website.

Colorado Gardening Calendar for November 2023

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

If you haven’t already, it’s time to clean out your garden beds. Photo: Molly Gaines

Right on time, we’ve had our first freeze and snow here in Denver. Yet my garden still sits, hanging on for dear life, in desperate need of clearing, composting, amending and mulching. I guess I’ve been in denial, holding on to my fading zinnias and still-green tomatoes, enjoying this gorgeous fall with its warm temperatures and prolonged tree color. Luckily, November is still likely to bring a few mild days. So now’s the time to make a list and check the boxes before everything goes into hibernation until next spring.

A Gardener’s Yard and Garden Checklist for November 

Vegetable Garden

• Clear all plantings and compost. Pests and diseases can overwinter in plant debris and wreak havoc on next year’s garden (aphids, anyone?). 
• Oh my do I have a lot of green tomatoes, around 40 at last count. If you’ve been covering plants to extend the season, it’s time for your final harvest. For ideas on storing late-season produce, visit this helpful page from the University of Minnesota’s Extension office. For a fun recipe from Martha Stewart on cooking green tomatoes, visit here.  
• Spread and work compost into your garden beds before the ground freezes. 

Harvest any remaining vegetables that were lucky to survive the initial frosts. Photo: Molly Gaines

Trees and Shrubs

• Remove dead tree branches, including those on shrubs and roses. 
• Water new fall plantings weekly, including trees, and other perennials until the ground freezes. It’s important to water throughout the winter during warm, dry periods to support healthy roots and next year’s growth. 
• Wrap the trunks of young trees to prevent sunscald, which can occur during periods of alternate warming and freezing in the winter. “On at Thanksgiving, off on tax day” is a good rule of thumb for utilizing tree wrap.
• Protect evergreens with burlap plant bags to prevent them from drying out. 

Lawn Care 

• Fertilize a final time; in Denver this can be done up until Thanksgiving. For more information about fall lawn fertilization from PlantTalk Colorado, visit here. 
• It’s time to blow out and shut off irrigation if you haven’t already. Rake up leaves and either compost or mow over them for garden bed mulch.

Perennial Beds 

• If you haven’t cut back grasses and flowering perennials for the year, let them be. Dead plant stems and leaves provide habitat for moths, beneficial garden insects and butterflies that overwinter.
• Continue watering until the ground freezes. This is especially important for all new plantings. 
• As long as the soil is workable, plant bulbs for spring flowers in the next few weeks. They should still have time to establish before the ground freezes. Water in well. 
• Dig up and save dahlia tubers. Allow them to harden off for two weeks after frost before storing. Find directions here.

Other Projects 

• Bring indoors any houseplants or other potted plants you’d like to save. Hopefully, they’ve survived under heavy protection so far.
• Sanitize, sharpen, and oil tools, including the lawnmower blade. Come spring, you’ll be grateful these tools are ready to go. 

Hope it’s not too late to get houseplants indoors! Photo: Molly Gaines

Follow Up: Denver’s Tree Canopy Survey 

The City of Denver published the results of the September survey of residents about Denver’s tree canopy — and the future of our urban forest. Overall, support for private tree protection is strong. A few points to note from the survey summary: 

• More than 85% of all respondents support private tree protection for trees over 18 inches in diameter. 
• There are differences between renters (17.49% or 378 responses) and owners (75.8% or 1,638 responses) with renters more supportive of the city taking over tree maintenance and for minimum shade requirements. 
• There is overall support for a fee to help maintain street trees, which is highest at the $50-75k income bracket (75%) and is lower for the highest and lowest income brackets ($150k+ at 67.05% support and <$25k at 66.67% support).

Remember to visit the CSU Extension Yard and Garden website for more gardening tips and to prepare for next year’s season. You can also reach out to the Colorado Master Gardener’s office with any yard or gardening questions: 720.913.5270 – we’re available year-round!

Colorado Gardening Calendar for October 2023

By Margerie Hicks, CSU Extension – Denver Master Gardener since 2010

October is my favorite month to enjoy the vibrant, intense colors and crisp autumn breezes of Colorado. Gardeners need to adjust their routines to ensure a healthy, beautiful garden next year by completing the maintenance tasks outlined here that apply to your garden.

Vegetable Garden

Harvesting carrots and beets photo by a-lesa on iStock

• Harvest and Preserve: Your vegetable garden may still be yielding some late-season treasures. Harvest your remaining root vegetables and squash. Store them in a cool dry place for use throughout the winter. Consider canning or freezing surplus produce or donating some to a food bank. For canning information click here. The first frost will probably occur mid-month, so don’t be caught harvesting one night in a freezing drizzle (I’m speaking from experience); observe the weather reports each day.
• Clean and Compost: Remove spent plants and weeds from your garden beds to prevent diseases and pests from overwintering. Compost healthy plant material to create nutrient-rich soil for next spring. Learn more about composting techniques here.
• Plant Cover Crops: Protect your garden’s soil during the harsh winter months by sowing cover crops like winter rye. These cover crops help prevent soil erosion, suppress weeds, and improve soil structure. When spring arrives, you can simply turn them under to add organic matter to your soil.

Trees and Shrubs

• Blow out the sprinkler system: When water freezes the pipes may crack.
• Wrap the trunks of trees that have been planted in the last one or two years:  Click here for details.
• Prune and trim: See this Colorado State Forest Service pruning guide. Do not prune spring flowering shrubs or you will be removing next year’s blooms. In the future, prune these soon after the blooms fade. 
• Irrigate: Continue to water, and plan for monthly watering all winter on days the temperature is above 40 degrees Fahrenheit.

Lawn Care

child playing in leaves photo by Scott Webb on Unsplash.com

• Rake leaves:  First form big piles so the children in your life can play in them. Then compost the leaves at home or take them, ideally in paper bags, to one of the leaf drop sites provided by the City of Denver. Click here for locations, dates, and times.
• Fertilize: Click here for details on proper lawn fertilization.
• Aerate: Unless your lawn has been aerated since spring, see the sub section of this fact sheet called “Core Cultivation or Aerating” to learn more.

Perennial Flower Beds

Planting tulip bulbs photo by LianeM on iStock

• Plant spring bulbs: Tulip, hyacinth, crocus, daffodil and other spring blooming bulbs can be planted when the weather gets cool. See this fact sheet for important considerations in selecting and planting bulbs.
• Divide and transplant: October is the ideal time to divide overgrown perennials. This process rejuvenates the plants and can also provide you with new additions to your garden. Transplant them to new areas or share them with fellow gardeners.
• Cut back and clean: Trim back faded perennial foliage and remove debris from your flower beds. Consider leaving some plants uncut, such as ornamental grasses and dried echinacea blossoms, as winter habitat and seeds for birds. These and other plants, such as Autumn Joy sedum, provide winter interest to the garden.

Annual Flower Beds

Ornamental Cabbage photo by Santi WiWatchaikul on iStock

• Plant cool season annuals: Extend the beauty of your garden by introducing cool season annuals like pansies, violas, and ornamental kale or cabbage. These hardy plants can withstand the cooler temperatures of late fall and early winter, adding vibrant color to your landscape.
• Enjoy blooms inside: Before the frost, cut any remaining blooms, such as roses, bring them in the house, and put in vases to enjoy the last summer color.

Other Tasks

• Bring in house plants from the patio before the inevitable frost. First, hose off the summer dust and any insects, then let them dry while still outside.
• Wash and store pots; clean, sharpen, and oil garden tools; store for the winter.

October is a transitional month in Colorado gardening. Use this month to prepare your garden for the winter months ahead. Remember to adapt these guidelines to your specific microclimate and garden conditions, and always consult research-based resources such as https://extension.colostate.edu/topic-areas/yard-garden/ for the most accurate advice. Happy gardening.

Colorado Gardening Calendar for September 2023

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

Winecups reaching for water. Photo by Valerie Podmore

When I went on my (mostly) daily morning walk (I’m writing this in the 3^rd week of August by the way), the temperature was a lovely mid 70’s and my walking buddy said, “this is a really nice morning, almost like fall.” As we’ve had so many hot, hot July and August days, the thought of experiencing cooler ones is quite appealing! I’m sure our plants will enjoy that as well (not the walking part of course haha). Let’s look at our gardening to-dos for this month.

Vegetable Garden

Ok I admit, my first attempts at veggie gardening are not going great, mostly because I’ve not watered properly, I think. It could also be the location has much more shade than initially imagined. Remember that right plant, right place mantra? I didn’t! In any case, here are some tasks to perform this month for those of you who actually have real vegetables growing.

• Continue to harvest any ripe summer vegetables and clear out fallen leaves, weeds and other disease-causing debris.
• Plant cool weather vegetables now as they mature quickly and love less heat. These include lettuce, kale, arugula, Swiss chard, and spinach. Here’s a timely post on how to extend our growing season.
• Don’t forget to continue watering because we all know that Colorado can throw crazy weather at us…and it follows then to prepare for cold weather snaps too. There’s nothing worse than working so hard to grow something only to have it destroyed by Mother Nature. 

Trees and Shrubs

• Oh that watering thing again. It’s like some sort of Tamagotchi game (showing my age!) to make us desperately try to keep our plants alive! Keep an eye on the weather and water deeply when precipitation has been scarce. This information sheet has EVERYTHING you want to know about water.
• While we can prune, if necessary, try to avoid it during this month. Make note of branches that need attention and save the tasks for late winter or early spring.
• We may not realize it, but September’s cooler temperatures make it a good time to plant trees and shrubs as it gives enough time for the plant to acclimate in the warmer soil and prepare for the winter months. Here’s a great article on this very idea.

Lawn Care 

• This is a great month to revive our lawns by aerating and fertilizing or overseeding bare spots.
• As mentioned above, watering is still important to keep our lawns healthy so let’s continue caring for our lawns as fall is not the time to stop the good lawn care practices we’ve undertaken throughout the year.
• Tired of dealing with lawn? Now’s the time to start to plan a turf conversion. This page offers practical tips.

‘Autumn Joy’ sedum’s dusty pink blooms pop in September and last till frost. Photo by Linda McDonnell

Perennial Flower Beds 

• This is a perfect time to start cleaning up our plants as they begin to go dormant, by clearing away dead and mushy leaves, fruits or weeds which can cause disease.
• This quick read has good advice on clearing up the garden in the fall and pollinator-friendly clean up tips can be found here.
• Divide early blooming perennials such as iris, lily, hostas, bleeding hearts, and other bulb or tuberous species to keep them from crowding each other too much.
• For anyone who has a spare hour and some, and REALLY wants to nerd out on fall plant advice, take a look at this awesome video!

Annual Flower Beds

Because I’m lazy, I prefer perennial plants but of course we can’t minimize the impact that annuals have in the garden. The colors and variety are just so great!

• Make note of those annuals that you will want to replace next year.
• Get your pots of Chrysanthemums or pansies busted out to provide fall color, as these plants prefer cooler weather and add that color we sometimes need to combat that seasonal affective disorder that we have (well I’m speaking for myself here!).

As always, visit the CSU Extension Yard and Garden website for more gardening tips.

Colorado Gardening Calendar for August 2023

By: Gail Leidigh CSU Extension-Denver Master Gardener since 2021

August is a fabulous month for enjoying your garden. Much of the work from earlier in the season will have paid off at this point. Since August is often hot and dry, it’s important to make sure your garden is getting the right amount of water, and to remain observant for stressed plants. Mark your calendar to get these gardening to-do’s done in your yard and garden.

Also this month and through September 15^th, CSU Extension is accepting applications for the next Colorado Master Gardener class. To learn more about our program, explore the resources at www.ColoradoMasterGardener.org and read Let’s Grow Together: Becoming a Colorado Master Gardener by Felicia Brower.

The vegetable garden at the Denver County Extension office. Photo: Merrill Kingsbury

A Yard and Garden Checklist for August

Vegetable Garden

• As your veggies ripen, harvest them, and if you cannot eat them right away, check out these good ideas to preserve them for later from Master Gardener Lois Margolin.
• How are your tomatoes doing? Growing tomatoes in Colorado can be tricky, with our wide temperature ranges and winds that prevent pollination. Some ideas for helping with your tomato problems can be found in this video on the PlantTalk website.
• Extend your gardening time by planting cool season vegetables such as peas, broccoli, and kale.

Trees and Shrubs

• Pay attention to signs of stress and desiccation in woody plants, and supplement with water as needed.
• Prune back summer blooming shrubs that have finished flowering, and that will bloom next year on this season’s growth. (It’s too late to prune spring blooming shrubs such as forsythia and lilac.)
• Always avoid trimming trees when they are water stressed by hot and dry conditions – they need to conserve all the energy they can this time of year.

Lawn Care

• During periods of high temperatures, a lawn may need as much as 2.5 inches of water or more per week.
• Mid to late August is a good time to over-seed bare spots in the lawn.
• The best defense against weeds in the lawn is thick and healthy grass, and you can encourage this by cutting the grass high – about 2.5 inches or higher.

Photo: Gail Leidigh

Perennial Flower Beds

• Some plants will start going to seed this time of year. If you don’t want the plant to self-seed, seed heads can be cut back. Or leave the seeds for the birds to enjoy.
• Weed ‘em and reap: Continue weeding the yard and gardens now, and reap the rewards later.
• Take note of what worked this year and what did not. Many perennials will be on sale at the end of summer and this fall, and it is a great time to fill in bare spots or replace plants that didn’t make it.

Annual Flower Beds

• Check the soil moisture in pots and hanging baskets frequently, as they will dry out quickly in the summer heat and wind.
• Clear and thin out plants that are fading, and make room for fall annuals that love the heat such as angelonia, ornamental kale, and daisy rudbeckia.
• Dead-head to encourage growth of new blooms.

Enjoy your garden this month!