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 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 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!

Colorado Gardening Calendar for July 2023

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

Roses in bloom for a “hot” minute, photo by Valerie Podmore

With all the precipitation we’ve had this year, our gardens have been busting out all over with beautiful blooms, vegetables are loving it and of course weeds are growing like gangbusters. I bet many of us have not really had to water much yet…how great is that?!

This month let’s get out there and keep on top of the bounty that this amazing weather has brought us, knowing that in Colorado the weather can turn on a dime, so we need to be prepared for anything.

Vegetable Garden

• This is the month when we can start harvesting our ripening vegetables, fruits, and herbs.
• Look to plant vegetables for fall harvest. This information sheet has great ideas!
• Since July is typically hot and dry, we may need to water but make sure not to water from above to prevent mildew and other maladies from forming.
• This article is a great overall guide on caring for veggie gardens. I’ve bookmarked it for my future reference as a beginner veg gardener!

Trees and Shrubs

• While we’ve had ample water this year, we still need to watch the weather and make sure our trees and shrubs are adequately watered when we’ve received no precipitation in 10-14 days to prevent disease. Denver Water has a nice, succinct guide to help.
• Emerald Ash Borer has been detected in a small area of Littleton and Carbondale (both new locations) and this information can help you plan ahead if you have ash trees.
• Our landscape shrubs are probably growing beautifully right now and seeing some dead branches might drive us crazy (us = me), so know that while this is probably not the prime month for pruning, removing these dead canes can help. This pruning guide contains so much great information I’ve had to read it over more than once.

Lawn Care

• Our lawns are probably quite happy with all the moisture we’ve received, and let’s keep them thriving with proper care.
• Fertilizing can help if done correctly at the right time.
• If you are considering converting your lawn to less water-intensive landscaping, this info sheet contains a multitude of conversion methods and ideas.

Bunny in my garden, relaxing and digesting the flower leaves it just ate, grrrr! photo by Valerie Podmore

Perennial/Annual Flower Beds

• Both perennials and annuals can benefit from deadheading to promote more flowering and preventing them going to seed (if that’s what you want).
• Pull those weeds to prevent them taking over your flower garden!
• This document has a plethora of information about annuals and perennials during low-water periods because let’s be honest, we WILL get back to a lower water situation soon enough.

Oh, just one more thing (a la Columbo!), don’t forget that the “wonderful” Japanese Beetle will begin to make its appearance this month to destroy our hard work, so take a look at this article to learn more on this pest and how to battle it.

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

Colorado Gardening Calendar for June 2023

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

June is my favorite month in the garden – from the explosion of colorful blooming perennials and the promise of the summer harvest to the comfortable temperatures – it just doesn’t get any better. We’re also coming off a month of record-setting moisture, which makes the landscape greener and lusher than usual.

Early June columbines, coral bells & tulip foliage. Photo: Linda McDonnell

Our May gardening calendar covered the season-long essentials of weeding, mulching, and watering. Refer to it for those tips. On this post, let’s look at ways to keep plants healthy, troubleshoot potential issues, and enjoy the garden.

Trees and Shrubs

• Check apple, crabapple, mountain ash, and pear trees for fireblight, a bacterial disease that emerges in spring, especially when there’s been wet, warm weather. Look for curled, bent shoots with brown or black leaves, and limbs shaped like a shepherd’s hook. Learn how to properly treat fireblight here.

Fireblight on an apple tree. Photo:  I, Paethon via Wikimedia Commons

• Suckers are shoots that spring up from the base of the tree trunk or root system. Aspen, sumac, chokecherry, and plum trees are prone to suckering. Suckers can indicate the tree is stressed. Hand prune suckers where they attach to the trunk or root system. CSU reports Sucker Stopper RTU™ may help with control.

• Prune spring flowering shrubs now to control their size/shape, remove dead wood, increase air circulation, and improve flowering next year. Find tips here.

Vegetables and Herbs

• CSU’s Grow & Give program is a way to share your harvest with the community. Consider signing up to donate excess produce on the Grow & Give website. You’ll also find excellent growing tips and insect/disease help on the site.

• If you’re growing in containers, remember that they dry out quickly. Check daily as temperatures rise. Mulch will help retain moisture.

• For the best flavor, remove flower buds from culinary herbs.

It’s hard to pluck lovely chive blooms! Photo: Pitsch from Pixabay

Perennials and Spring Flowering Bulbs

• When flowers fade, snip tulip and daffodil flower stems at the base. Leave the foliage until it yellows and goes limp. As it dies back it’ll provide valuable nutrients to the bulb which will help with next year’s flower production. Apply bulb food now too. If you already pulled the foliage, you could still add fertilizer.

• Deadheading, or removing flowers that have finished blooming is a matter of personal preference. Deadheaders cite encouraging re-flowering, creating a tidier landscape, and reducing unwanted reseeding as motivators. Others prefer a more natural appearance that provides food and shelter for birds and other animals, reseeds freely, and features interesting seed heads. Many gardeners deadhead some, but not all plants.

• If you deadhead perennials, consider the plant’s growth habit when pruning. For example, cut the flower stem about ¼” above the next set of leaves or an emerging bud on upright clumping perennials such as echinacea. Shear mounding plants – such as catmint, golden storksbill, and cranesbill geranium – down to about three inches. This is quick and easy. They’ll look scruffy but rebound quickly.

• Ornamental grasses and most climbing roses bloom once a season so deadhead for aesthetics or to remove diseased foliage.

Shear golden storksbill to get more flowers & contain size. Photo: Linda McDonnell

• To keep mid to late season blooming perennials from flopping, reduce their height by 25-30% in early to mid-June before flower buds emerge. This Chelsea Chop promotes side branching, creates shorter, stockier plants, and delays flowering by a week or two. Good candidates include soft stemmed, clumping plants such as New England aster, chrysanthemum, and false dragonhead.

Manage Unwelcomed Visitors

• Creeping bellflower (Campanula rapunculoides) is prolific in Denver. Treat it as a weed. Unlike other campanula species, it’s a fast growing, sharp elbowed invasive that will choke out any plant in its way. It has heart-shaped leaves at its base, which become narrower as they move up the stalk, and green to reddish stems. Mature plants have stubborn, deep, white fibrous roots. Left unchecked it can reach three feet tall and produce nodding light blue bell-shaped flowers on one side of the stem. Control by digging out the roots and removing new growth as it pops up. If you’re plagued with this thuggish plant, this handout from Wisconsin Extension is a must read.

You’ll regret letting creeping bellflower get this big! Photo: Linda McDonnell

• Aphids are back. These soft bodied, green, tan, or orange sesame seed shaped insects are relatively harmless to shade trees and ornamental plants. They suck on tender young foliage and mark foliage with a sticky honeydew secretion. Lady beetles, green lacewings and parasitic wasps feast on aphids. A strong stream of water may be enough to dislodge aphids without compromising biodiversity. Insecticidal soaps can also be effective.

• Aphids on food crops can be more problematic. See this University of Utah article for advice.

• Rabbits are cute but can be destructive to plants and turf. Find tips for creating barriers and using safe repellants here.  

• Japanese beetles will emerge from the ground in late June or early July. Get ready to pick and drown or stomp them. Review CSU’s report for details and watch for our July JB post for helpful tips.

Lawn Care

• Water only when needed and in compliance with Denver Water Department’s rules. CSU’s lawncare handout can help you use water responsibly while maintaining a healthy lawn.

I hope you enjoy this beautiful time of the year. Remember to visit the CSU Extension Yard and Garden website https://extension.colostate.edu/topic-areas/yard-garden) for more Colorado gardening tips and solutions.

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.

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!

Colorado Gardening Calendar for November 2022

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

Anything can happen in a Colorado November: our first hard freeze (or the second or the third), or nighttime temperatures stuck at 45F. Lawns and gardens can suffer from heavy wet snow (with the splintered tree limbs littering the streets to prove it) or prolonged dryness that has gardeners alternating watering with leaf raking. Despite the unpredictability of autumn, winter will eventually arrive (probably with two feet of snow on Thanksgiving Eve), so our focus this month is on closing out the 2022 season and preparing for Spring 2023. 

VEGETABLES

• Harvest any remaining vegetables; we can have a killing frost and/or snow that will wither produce anytime now. Farm Calculators offers an extensive list of veggies for autumn harvest; if mild weather has gifted us with green tomatoes, try ripening some to use on Thanksgiving! Minnesota Extension has compiled some great hints on harvesting AND storing late-season produce.
• Finish cleanup now while temperatures remain mild. Pests and diseases will overwinter in plant debris and afflict the garden next spring and summer – and no one feels like working outside in a December snow squall!
• Spread compost over the soil and turn it in – it feeds the microscopic critters that will deliver nutrients to your plants’ roots next year.

TREES AND SHRUBS

• Pruning trees and shrubs can wait a few months, according to the schedules outlined in the Plant Talk articles Pruning Shrubs and Pruning Shade Trees. Dead tree branches, however, should be removed ASAP so they don’t become a hazard in heavy snow accumulations. (Many arborists offer discounts for off-season services.) Ditto for all dead bits on shrubs and roses.
• Keep watering weekly until the ground freezes – usually around Thanksgiving at Denver’s elevation. 
• Check mulch levels to ensure that soil moisture remains adequate to maintain healthy roots. Mulch should cover the root balls without crowding the stems or trunks. 
• Irrigation during winter warm periods is also key to helping roots support plant growth next year. Consult the Extension Fact Sheet “Fall and Winter Watering” for details on winter watering.
• Wrap the trunks of trees too young to have formed bark to prevent sunscalding during periods of alternate warming and freezing in the winter. During warm periods, tree trunks take up water into their cells, which then burst when temperatures drop below freezing, killing bark and conductive tissue. “On at Thanksgiving, off on tax day” is a good rule of thumb for utilizing tree wrap.
• Consider using protection like plant bags and burlap around evergreens prone to drying out in winter winds. 
• Put rose collars around your roses and fill the collars with leaves for insulation, or mound soil over the bud union of each plant.

PERENNIALS

• Make sure that nonxeric and new xeric/native perennial plants are mulched to a depth of at least one-and-a-half to two inches. Pull the mulch back from the crowns to forestall crown rot and discourage pests from burrowing around the plant.
• Keep watering perennials until the ground freezes and throughout the winter as prescribed by the fact sheet referenced above.
• Postponing deadheading and cutting perennials back until spring offers several advantages to your garden: many perennials produce seedheads and stems that offer cold-weather food and shelter to birds, beneficial insects, and other wildlife; intact stems also protect crowns from freezing and catch snow to deliver more moisture to the plants. 
• It’s a bit outside the recommended planting time, but If you still have bulbs to plant and the soil is workable, do it now. Since roots will have less time to develop, flowering may be reduced, but you still may enjoy spring blossoms. Make sure to water them in well. 

LAWNS

• Rake up leaves so they don’t mat on the turf and promote mold growth. Running a mower over piles of leaves will produce free mulch to spread over plant beds (and free nutrients as the leaves decompose)!
• Blow out and shut off sprinkler systems if you haven’t done so already. If time and weather permit and the turf looks dry, irrigate one more time.

MISCELLANEOUS

• Clean, sharpen, and oil tools; get that lawnmower blade sharpened while you’re not distracted by spring gardening tasks.
• Consider what plants to add next year – gardening catalogs will start arriving next month! And continue to contact Denver County Extension with all your gardening questions.

ONE MORE THING

It’s been my pleasure to contribute to this blog this season, but my short posts can cover only a few essentials. Therefore, here’s a fall task list that not only adds another dimension to your fall garden experience but also allows me to make a small homage to a most distinguished horticulturist whom we lost this year: Ten Key Tips for the Fall Garden.