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 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 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 October 2022

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

Woohoo October! Photo by Pixabay

It’s Pumpkin Spice time…no, not the drink, the gardening season! October is one of the best months for cleaning up the garden in preparation for the impending end of the season and of course doing pumpkin things! Mark your calendar to get these gardening to-do’s done in your yard and garden.

Vegetable Garden

• Continue to harvest your vegetables which you planted both earlier in the season and in early fall.
• Think about building cold frames or some sort of protective covering to help your veggies last as long as possible with the colder weather this month.
• Cover crops can help build your soil for next year’s planting.
• If (unlike me) you have kept your herbs alive this season, maybe give herb preserving a try.
• Take a look at this article about Pumpkin Habanero peppers…talk about Pumpkin SPICE!

Trees and Shrubs

• Young trees’ trunks (2” and less) will need to be wrapped to protect from sunscald in winter (from November to April).
• Pay attention to watering, making a plan to water deeply every 4-6 weeks during dry fall and winter months.
• More detailed tree and shrub care information can be found here.

Lawn Care 

• Lawn aeration can still be performed early in the month.
• Because we can have our first frost of the season anytime this month (average first frost is around October 6^th), this is time to winterize your sprinkler system. Good advice even if you don’t do this yourself. 
• Oh hooray! LEAF CLEANUP.
• In addition to the above, here is the Leaf Drop information for 2022 in Denver.

Perennial Flower Beds 

• If you didn’t plant any spring blooming bulbs yet, get ‘er done this month! 
• Early in the month is a great time to divide and transplant summer blooming perennials before the cold moves in.
• Here is a great pollinator-friendly post on fall garden clean-up if you are looking to help our friends through the winter.
• Working on winterizing your plants will help them survive for next year’s growing season.

Annual Flower Beds

• Pansies are a great way to get late season color into your garden.

Other Tasks

• Houseplants that were outdoors will want to come back in when the nighttime temps fall below 50 degrees. Make sure to give them a good clean-off of creepy crawlies before bringing them inside!
• Clean your tools for next year.

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

Planning a Less-Lawn Yard

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

Many Coloradans are swapping out their bluegrass lawns for less water-hungry and more regionally appropriate landscapes. This change in attitudes may be motivated by this summer’s brutal heat, need to conserve water, wildfires, desire to support pollinators, or the goal to spend less money on lawn upkeep – or a combination of these factors.

Governments are also getting behind the concept. Aurora recently approved legislature limiting the installation of turf grass in new housing developments starting in 2023.

The state of Colorado is developing a turf replacement program for homeowners to go into effect next year, possibly with monetary rebates, and administered by the Colorado Water Conservation Board. (Keep up with the board’s progress by subscribing to their newsletter.)

If you are considering converting all or part of your turf grass to a water-smart landscape, fall and winter are good times to begin the planning process.

Late summer at The Gardens at Spring Creek in Fort Collins. Photo: Linda McDonnell

Here are some practical suggestions to help you get started.

Form follows function is a time-honored design principle. Applied to a yard rehab it means considering how your yard is used before you ever think about how it looks. Do you need space for kids to play? Dine or entertain outdoors? Have dogs? Consider practical needs such as wide pathways to doors and seating areas (36-42” is recommended), storage for trash carts and clearance to roll them to the curb, and landing spots for passengers getting in and out of cars.

Lawn conversions don’t have to be all-or-nothing. Consider starting with a back or front yard, or a difficult to irrigate section of the lawn. Xeriscaping: Retrofit Your Yard offers excellent suggestions on selecting a site.

Keep what you can. Take a hard look at the plants in your yard and how they fit in the new scheme. You can’t move a 25’ conifer but relocating shrubs and xeric herbaceous perennials is doable and budget-friendly.

Hardscape – pavers, gravel, and rocks – may already be in place or can be relocated. Think about it: hardscape doesn’t need to be watered or mowed! If the budget allows, be generous with the use of hardscape in your new plan.

Gather inspiration and knowledge. Visit public gardens with xeric gardens such as Denver Botanic Gardens, Aurora’s Water-Wise Garden, or The Gardens at Spring Creek. Take photos and note plant names and combinations. If you need help identifying plant names, send your photos to the Denver Master Gardeners at the Denver Botanic Gardens for identification (gardeninghelp@botanicgardens.org).

CSU has a treasure trove of helpful information here.  Colorado Native Plant Society, Plant Select, and Denver Water are good resources, too.

Be realistic. Consider how much time you have to devote to this project, your skill level, and your budget. Will you do all or some of the work, hire help, or enlist family and friends? If you are not sure where to start, you may want to consult a garden designer who’s in sync with your goals.

Expect less work, but not no work. Xeric plants need to be irrigated until established, which could run one to two seasons, and during periods of prolonged drought. It is also critical, especially in the early days, not to let weeds take over. Initially there will be a lot of open ground and weeds would love to fill it up.

Don’t forget community regulations. If your neighborhood has covenant restrictions or a review process for landscape changes, you will need to submit your plan with enough lead time to have it approved before the project begins.             

Denver neighbors embracing less-lawn gardening. Photo: Linda McDonnell

Once you’re armed with your plan you can tackle removing grass. Fall is a good time to start, particularly if you want to use the solarizing process, an herbicide-free method to kill grass. Find instructions here. CSU also provides instruction on the proper and safest use of herbicides to eliminate turf here.

Exchanging traditional lawns for creative, ecologically sustainable landscapes is a smart practice that is likely here to stay. If you’ve converted a traditional lawn and have additional tips, we welcome your input in the comment section.

Colorado Gardening Calendar for SEPTEMBER 2022

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

Summer’s not done yet! by Valerie Podmore

Let’s not get downhearted at the impending end of growing season! September is one of the best months for continuing harvests, enjoying our gardens, and yes, preparing for the end of summer (sad face). Mark your calendar to get these gardening to-do’s done in your yard and garden.

Vegetable Garden

• Continue consistent watering practices. We might be cooling down, but we are still dry, so don’t let your hard work “die on the vine!”
• Plant fall vegetables! Some do really well in cooler weather and ripen quickly for harvest, such as lettuce, kale, arugula, Swiss chard, and spinach which can be direct seeded.
• Save heirloom plant seeds if you are looking to start your own plants for next season.
• Get your plant covers at the ready just in case we have a (pretty typical) cold snap or just in case temperatures dip lower than your veggies enjoy.
• Make sure to clear away any dead vegetation to prevent disease or pest proliferation.

mmmmm….the fruits of our labors. Photo by Valerie Podmore

Trees and Shrubs

• Water, water, water! Just like our vegetable gardens, our trees and shrubs need to be consistently watered. Weekly is a good schedule, but this fact sheet provides very thorough advice.
• Trim only branches or limbs which are damaged or diseased at this time.
• Be careful with fertilizing trees and shrubs. This link has good information on fertilization if there’s been particularly dry weather (when is it not?).
• While planting in fall might not be the #1 time, it’s still possible to find discounted plants and if you finish before the end of October, your tree or shrub will have some time to establish itself before the cold of winter.

Lawn Care

• Aerate this month to allow oxygen to get to the roots of your grass. This is an awesome turfgrass post for more information.
• Water deeply, giving your grass a good, long drink. Weekly for even 45 minutes is more beneficial than more often for less time.
• This great fact sheet has probably everything you need to know for keeping your lawn healthy.
• While the scourge of Japanese Beetles might be behind us, this is a prime time to apply grub-killers like grubGONE! and GrubEx to turf to help prevent them returning.

Perennial Flower Beds

• Water (I know, it’s like déjà vu!) weekly until the ground freezes to give the roots a chance to develop before winter.
• Cut back spent plants but consider leaving some stems and seed pods in place for pollinators and birds. This post from our Routt County Extension friends posits a different way of thinking about cleaning up (or not!) the season’s leftovers.
• Look at what needs filling in or doesn’t work and make plan for spring.
• Purchase fall planted bulbs – who doesn’t love plant shopping? This is the time that plant stores, catalogs or online sellers are stocking up so go crazy!

I can’t wait to shop! Photo by Pixabay

Annual Flower Beds

• Clean up annuals in containers and sanitize any pots you’ve emptied.
• Get some fall color such as chrysanthemums or pansies which overwinter quite well if mulched properly.

Other Projects

• KEEP WEEDING! That is all.
• Start prepping houseplants that have been outside to come back inside for winter. Check out this post for details.
• Finally, this is the month when Colorado Master Gardener program applications will begin! These will be posted on our main website with applications open September 1 – October 16. Do you or someone you know want to apply? Please DO!

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

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

Butterfly on lavender. Photo from Pixabay

So, who had the fifth earliest 90-degree day and the eleventh latest spring snowstorm in May on their garden bingo cards last month? Well, it’s June and who knows what else Mother Nature will throw at us! 

Thank you to those who attended the CMG Plant Sale during the great snowstorm of May 2022. Likely, you’ve either have planted your new purchases or will be doing so soon! 

JUNE is one of the best months for being happy that we can go outside into our gardens and watch (or MAKE) them grow. Mark your calendar to get these gardening to-do’s done in your yard and garden.

Vegetable Garden

• If you’ve planted your cool season-veggies (peas, lettuce, kale, and spinach) last month, this is the time to harvest to prevent these going to seed.
• Warm-season plants like tomatoes, peppers, and eggplant will thank you for continuing to transplant them this month to keep your harvest going.
• Water evenly, close to the soil rather than overhead to prevent fungus and other plant diseases from forming.
• Don’t forget to continue to perform the most fun activity ever…WEEDING! You don’t want your lovely veggies having to compete with these evil garden monsters.
• Apply organic mulch to keep the moisture up and the weeds down. Untreated grass clippings (i.e., chemical-free) are a good option.
• Make sure to join the Grow and Give program which supplies fruits and veggies to folks in our local communities who might have a need for our extra bounties.

Trees and Shrubs

• If there has been no precipitation in a month, make sure to water your tree(s). Trust me even with the recent snow, we are still very dry.
• If you are thinking of doing more xeriscaping, take a look at this information sheet on trees, remembering that less water for the landscape means less for trees and shrubs as well if we don’t set up the landscape in a water-wise way.

Lawn Care

• As mentioned in last month’s calendar blog, Japanese beetle control at the grub stage by using products like GrubGONE! that contain bacillus thuringiensis var. galleriae (Btg) must be applied to turf in May and early June to take effect. Check with a local nursery regarding availability of these products or order them online. Consult this Extension fact sheet regarding Japanese beetles for advice on dealing with this pest throughout the summer.
• This information sheet gives great information on watering during a drought, which we are experiencing even with late moisture we received.
• This might be a good time to start looking at more xeric plants as mentioned above in the tree/shrub section. Colorado and the west are getting dryer and we could look at different ways to reduce our water use including cutting back on traditional, high water needs lawns. Watch for our upcoming blog post on this topic, too.

Perennial/Annual Flower Beds 

• Our perennials require good watering during the month, low-level, slow watering to prevent fungus and other plant diseases caused by over-head watering. This applies to annuals as well, whether in containers or beds, to prevent them from drying out.
• Dead heading (the practice of removing spent blooms) will keep new flowers blooming throughout the month.
• If you have iris plants that have been in place for 3-4 years, consider dividing them after they finish blooming to keep them growing strong…kind of like us cutting our hair!
• This article contains a trove of information on creating and maintaining a perennial flower bed.
• Low-water flowering plants information (for both perennials and annuals) can be found here. An awesome read!

In closing, as June is Colorado Pollinator Month, take a look at this post on how we can attract these very important animals to our gardens.  Also visit the CSU Extension Yard and Garden website for more gardening tips.

Colorado Gardening Calendar for May and 2022 Denver Master Gardener Plant Sale

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

May is the month when gardening really goes into high gear! Here are the areas and tasks to tackle this month:

VEGETABLES AND HERBS

• Mark your calendar for the return of the Denver Master Gardener Plant Sale on May 21-22 at Harvard Gulch Park. The selection can’t be beat if we do say so ourselves! For more information visit: Upcoming Events – Denver County Extension (colostate.edu).

• Veggies and herbs can be planted this month; be prepared to cover them if nighttime temperatures go below 40 degrees. It’s advisable to plant tomatoes when overnight temperatures are consistently above 50 degrees.

• Start weeding now, in all areas of the garden. Get ‘em while they’re young!

• Consult the Extension fact sheet Fertilizing the Vegetable Garden to determine if and when to apply fertilizer to your plants.

• Find hints for combatting vegetable pests in this list of CSU fact sheets.

LAWNS

• Make sure that hoses and sprinklers are in good condition; apply an inch of water to the lawn each week, except during rainy periods. Denver Water has some excellent suggestions regarding lawn irrigation and general care from May 1^st through September 30^th, when watering restrictions are in effect.

• Consider irrigating the lawn at night or in the early morning hours when evaporation is minimal. This can be a real turf AND water-saving measure in the hotter months, and it won’t promote diseases.

• Set mower blade height at two inches – higher grass keeps the soil moist and promotes good root growth.

• A thick thatch layer interferes with efficient watering and fertilization, so check for thatch and arrange for power-raking if the thatch is at least one-half inch thick.

• Products like GrubGONE! that contain bacillus thuringiensis var. galleriae (Btg) as a control against Japanese beetle grubs must be applied to turf in May and early June to take effect. Check with a local nursery regarding availability of these products or order them online. Consult this Extension fact sheet regarding Japanese beetles for advice on dealing with this pest throughout the summer.

• How lawns are watered, mowed, cultivated, and fertilized in their early growth will determine their appearance and health throughout the summer and fall (and perhaps for the next year as well). This fact sheet on lawn care outlines the best practices for tackling these tasks from now until fall.

May garden in Sunnyside, Denver. Photo by Terry Deem-Reilly

TREES AND SHRUBS

• Take a look at the garden to spot any “holes” that can be filled with a good-looking shrub, rose, or small tree – right now is when nurseries have the best selection. Be sure to call the Utility Locator Service at 811 before digging any large holes.

• Begin watering existing trees and shrubs deeply once a week and check to ensure that plants are well-mulched. Here’s helpful information on selecting the correct mulch for your plants.

• CSU Extension has published a tree recommendation list for the Front Range and fact sheets on native trees and native shrubs that can be helpful in deciding what to add to your garden.

• Start checking for pests; they will become more active as the weather warms and our spring rainfall commences (we hope). Consult this list of CSU fact sheets for information on specific insects and controls. When selecting pest controls, consider their effects on beneficial insects!

• Now’s the time to apply copper spray to susceptible trees such as apples, pears, quince and crabapples, to prevent fire blight.

• Finish spring fertilization and pruning of roses; make sure to apply two inches of mulch at the base of each plant and water newly planted roses twice a week for the first two or three weeks to promote root growth. Once established, roses will appreciate getting at least an inch of water weekly as temperatures rise.

ANNUALS AND PERENNIALS

• Perennials can be hardened off and planted now; wait until at least the last average frost date in mid-May to fill annual beds and containers. Keep frost covers handy if we have one or two chilly nights before Memorial Day.

• Summer bulbs can be planted now, so check them out at your local nurseries. It’s also a great time to divide summer and fall blooming perennials, find excellent info here.

• Treat pollinators by seeding bare spots with their favorite annual plants, including borage, dill, zinnia, and/or cosmos. Plant as recommended by the seed packets and water. Seeds will germinate in a week or two; sprinkle the seedlings gently every few days and wait for the bees and butterflies to arrive! More pollinators mean more tomatoes, squash, fruit, etc., etc.

May certainly is a busy month in the garden! What’s on your to-do list?

Colorado Gardening Calendar for March

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

Crocus, the harbingers of spring! Photo credit: Pixabay

MARCH is one of the best months to whine about WHY ISN’T IT SPRING YET? then calm down, realize it’s almost here and daydream about sunny days in the garden. As I write this, there is still snow on the ground and more in the forecast (which is awesome sauce for our outdoor plants) but if you are like me, the instant March hits you think it’s time to get outside doing garden things. Slow down there cowboy, technically it’s still winter and there’s more planning and prepping to be done. Mark your calendar to get these gardening to-do’s done in your yard and garden.

Vegetable Garden

• Time to get your project management hat on and plot out your garden. You’ll find a plethora of landscape design apps online or you can use good old paper and pencil.
• Inventory your seeds and order any you might still need as well as any supplies for seed starting. 
• Cold tolerant veggies can be started in a cold frame or possibly outdoors if the daytime temperatures are consistently 40 degrees F or above – so pretty much the END of March.

Trees and Shrubs

• If precipitation is sparse (4 weeks without moisture), remember to water your trees and shrubs.  While we are doing well moisture-wise this year,  we know things change quickly in Colorado!
• This is a great time to prune summer flowering shrubs and dormant/shade trees. However, refrain from pruning early flowering shrubs such as spirea, lilac, and forsythia because they bloom on last year’s growth. 

Lawn Care 

• Early March is a great time to sharpen up your mower blades (try to contain your excitement!) and add or replace oil if applicable.
• If the ground is not frozen and your landscape not too dry (i.e. LATE March), you can aerate, which is the process of poking holes in the lawn and supplying the grass with air.

Perennial/Annual Flower Beds 

• Just like your veggies, get your seeds in order and ready to start them sprouting indoors.
• Check your bulbs and tubers in storage and think about what bulbs you can plant in spring for summer blooms.
• As with February, take stock of your current beds to see what might be lacking and needs new life. 
• Don’t worry too much about late season snow, as snow serves as an insulator on perennials that have broken dormancy and won’t harm plants.
• If you attended the Colorado Home and Garden Show in February, use the ideas you gained to plan for any changes you want to make. However, remember the motto of “right plant, right place” when planning your new additions.

Finally, (the bane of my current existence) review structures and hardscape, paying attention to needed repairs or changes. With luck this year my money tree will bloom profusely and help me pay for everything! 

Don’t forget to visit the CSU Extension Yard and Garden website for more gardening tips…and happy gardening!