Selecting The Best Mulch For Your Plants

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

Mulch makes an impact in so many ways – from water conservation to weed suppression, improved plant health to enhanced visual appeal – mulch seemingly has superpowers.

There are two general types of mulch – organic and inorganic.  Organic mulches include bark chips, straw, grass clippings, and dried leaves; gravel and small rocks are inorganic choices.  Which mulch to choose? The best advice is to match the mulch material to its intended use. Let’s take a look at some common mulch applications.

Shrubs, Trees and Perennial Beds

Bark Mulch

Three to four inches of bark mulch laid directly on the soil helps maintain moisture, reduce water use, and lower the soil temperature. Skip the landscape cloth and plastic barriers, which when left in place for multiple years, will impede water penetration, limit essential oxygen exchange, and inhibit root development.

Spring hyacinth bulb poking through bark mulch.

Leave a few inches of bare soil around the base of the plant (more for large shrubs and trees) to allow the plant to absorb moisture. Avoid mounding mulch around the trunk of trees – a “volcano” of mulch will hinder healthy root development. Do not mulch over the root ball of a newly planted tree.

When adding plants to the bed, rake the mulch away from the space before digging to avoid mixing the bark into the planting hole. Bark chips break down in soil and as they decompose, can rob soil of essential nitrogen. 

How much mulch do you need? A two cubic yard bag of mulch provides three inches of coverage over 216 square feet. This online calculator is handy for determining the quantity needed based on depth and coverage area. It calculates the number of bags or bulk quantity needed, or at least gives a good estimate.

Pea Gravel


Pea gravel (stones with diameters of less than one half inch) are highly effective mulches. Three inch deep coverage provides weed control and even more effective moisture infiltration than bark chips. During cold months, gravel mulch’s warming effect can increase biological activity down to one foot below ground, resulting in healthier, more resilient plants. Pea gravel is frequently the mulch of choice for xeric plants because it offers excellent drainage.

As with bark mulches, do not use landscape cloth or black plastic beneath pea gravel and move the mulch away from the crown of plants.

This Colorado State University (CSU) publication offers a complete review of mulch options; xeriscape mulches are discussed here.

Vegetable Gardens

According to CSU, “In general, mulching minimizes evaporation of water from the soil surface, reducing irrigation needs by around fifty percent. It helps stabilize soil moisture levels, thereby improving vegetable quality and encouraging the beneficial activity of organisms.”

Mulching also helps reduce soil compaction, can add organic matter to the soil, controls weeds, and modulates temperature extremes.  Bark chips are not recommended around vegetable plants but are useful as a garden path.

Black Plastic

Tomatoes, peppers, eggplants, and vines such as cucumbers, summer and winter squash, pumpkins, and numerous melons benefit from a layer of black plastic placed on the soil early in the season. The plastic warms the cool soil, allowing for earlier crop growth. Be sure to remove the plastic in the fall to preserve soil health. 

Early season zucchini plant in black plastic. Note the cutout around the plant’s base.

Grass Clippings

Grass clippings from lawns that are untreated by herbicides or pesticides make excellent vegetable garden mulch. Build up the mulch coverage by adding up to a quarter-inch of clippings, allow them to dry, and then repeat with another layer. This layering process prevents the grass from forming a thick, impenetrable mat which restricts the plant’s moisture absorption.

At the end of the season, turn the grass into the soil; it will break down and add organic matter.

This CSU publication contains more options for mulching a vegetable garden.

Turf Alternatives and Garden Containers

Many are rethinking conventional bluegrass lawns and opting to use mulch to replace portions of turf. Large rocks, pea gravel, and bark mulch are popular landscape accents, paths, or borders that reduce water use and create an interesting, practical aesthetic.

Ornamental garden containers can be topped off with a layer of mulch to help retain moisture and add a finished look to the planter.

For a rewarding and plentiful garden, don’t skimp on mulch this season!

May Gardening Calendar of Tasks & To Do’s

By: Lori Williams
Denver CSU Extension- Colorado Master Gardener since 2016

Happy May Day, gardeners! We’re getting closer to putting plants in the ground every day, woo! And we can all get even closer today (May 1) by ordering online for the Denver Master Gardener’s Plant Sale.

Beyond the fun of shopping the DMG Plant Sale, May is a busy and exciting time of year. There is a lot we can do to get ready for jumping into 2021’s growing season.

Survey your garden, as you clean things up.

  • Note what’s coming up, what pooped out, what needs transplanted to the right place and what are the right plants for bare spots.
  • Straighten the trellis, spray down the patio furniture and clean and disinfect the garden tools and containers that you’ll be using.

Healthy Soil

Soil is the foundation of gardening success, so give your established, new garden beds and future spots for plantings the best gift ever!

  • If you haven’t had a soil test done for your garden, go for it. It’s interesting, informative and guides your soil amending.
  • A recent Denver Master Gardeners blog post details the best practices and the importance of soil health in our gardens.


  • Harvest this rich organic matter from your bin, pile, or barrel and treat your garden. Gather it into a wheelbarrow or onto a tarp so you can easily move it around your yard to top dress garden beds and around plants throughout your garden. 
  • Creating and maintaining compost is well worth the effort.


  • Inspect your trees for any damage from Colorado’s weighty snowfalls and gusty winds. If an arborist is necessary, call to get on their schedule, they get busy fast.
  • Trees are beautiful and beneficial in so many ways. Maintaining them is central to their health and longevity. CSU Garden Notes 650-659 will provide you with essential tree care information.

Shrubs & Vines

  • May is prime time for pruning and shaping shrubs, vines and even roses.
  • Take time to prune and fertilize your roses early this month. They’ll love the attention and will reward you with blooms and color for months.



  • When outdoor temps are holding at a minimum of 40°F, hardy, cool season vegetable seeds like peas, lettuce, kale, and spinach can be direct sown into the prepped bed
  • More tender/warm season crops need nighttime temps to be reliably at a minimum of 50°F. Patience is truly a virtue in planting things like tomatoes, peppers, and eggplants.
  • Hardening off or acclimating delicate bedding plants prior to planting them outside is essential. Start by putting plants outdoors in a protected area for a few hours each day and then bring them inside. Gradually increase the amount of time outside over the next week to 10 days until they can be left out overnight.


Irrigation systems

  • Schedule to turn on your irrigation system to test the coverage patterns and actual amount of water reaching your garden.
  • It’s worth time and money to water wisely, minimize overspray and help Colorado conserve as much water as possible.
  • Program your system responsibly, Denver Water offers a watering guide by month.


  • Annuals are the color bombs and mainstays of many a patio pot and garden bed. Love them SO much and we enjoy them in not only our yards but all over town. Shop till you drop at your local nurseries, start them by seed, and plant them with abandon!
  • Use the CSU Annual Plant Trials to find the top performers for your garden.


  • Mulch is just like what we say about kindness: it’s (almost) free, spread it everywhere! Watch for more on mulch up next on the next Denver Master Gardener blog.

Happy gardening in May, enjoy!

Visit the CSU Extension Yard and Garden website for more gardening tips.

Wild About Natives: Native Shrubs for Colorado

By Kathy Roth, CSU Extension-Denver Master Gardener since 2018

April is Earth Month and Spring is in the air – what better way to celebrate than by adding low maintenance native shrubs to our yards? Native shrubs are an excellent choice because they originated in our state and will thrive in the amount of rainfall nature gives them.

They don’t want to be fertilized as they receive the nutrition they require from our native soil and can get overgrown, spindly or live shorter lives if planted in amended soil. Native shrubs are also more resistant to pests and diseases and more easily withstand our unusual weather extremes such as long cold spells, drying winds, and variable temperature fluctuations.

When designing a native landscape, consider the site’s moisture, light, elevation and soil conditions as well as the selected shrubs’ bloom time and mature height.  When possible, strive for season-long color to prolong enjoyment of your garden. Grouping plants by their water requirements is key when deciding where to place your native shrubs. All newly planted shrubs, even natives, need supplemental water to get established. But once established, these shrubs are the environmentally friendly choice, particularly in areas that are difficult to irrigate such as next to parkways and hardscape (patios, sidewalks, fences).

A myriad of online garden resources are available on the Colorado Extension website. Fact Sheet #7.422 “Native Shrubs for Colorado Landscapes” lists shrubs by mature height, moisture requirements, brief description and whether they are evergreen or deciduous.

Here a few favorites that I’ve grown successfully.

Large Shrubs (mature height over 6’)

Curl-leaf Mountain Mahogany: Cerococarpus ledifolius. Thick dark evergreen leaves with tiny feathery seed head.

Serviceberry: Amelanchier alnifolia. Arching branches with showy fragrant white flowers in Spring followed by blueberry type edible berries. Fall color is yellow to soft red.

American Plum/Wild Plum: Prunus americana. White flowers followed by leaves. Small dark purple plums great for jams and wildlife. Yellow to red Fall color. Can form thickets.

Hop Tree/Wafer Ash: Ptelea trifoliata. Caterpillars of swallowtail butterflies attracted to and feed on this. Drought and shade tolerant.

Western Chokecherry: Prunus virginiana melanocarpa. Shiny dark green leaves with creamy white flowers that yield dark purple sour berries. Gives reddish-orange to yellow Fall color.

Medium Shrubs (mature height 4-6”)

Utah Serviceberry: Amelanchier utahensis. Fragrant white flowers in Spring followed by edible blue berries. Yellow Fall foliage.

Three-leaf Sumac: Rhus trilobata. Arching branches of small yellow flowers followed by compound 3-lobed green leaves. Orange to red Fall color.

Golden CurrantRibes aureus. Erect branches that form clumps. Yellow Spring flowers. Resulting yellow to black fruit attracts wildlife. Orange to red Fall color.

Leadplant/False Indigo: Amorpha fruticose. Spikes of deep blue showy flowers. Drought and shade tolerant, deer resistant! Forms nodules on roots to fix nitrogen so is often used in prairie restoration. 

Apache Plume: Fallugia paradoxa. White, rose-like flowers; fuzzy pinkish seed heads appear that linger all summer. Xeric.

Small Shrubs (less than 4’ at mature height)

Silver Sagebrush; Artemisia cana. Mounding gnarled aromatic silver leaves.

Kinnikinnik: Arctostaphylos ova-usi. Mat-forming evergreen with pink flowers followed by red fruits. Grows well in light shade, such as under large pines.

Creeping Oregon Grape-Holly: Mahonia repens. Ground cover, blue green leaves turn purplish in winter. Shade tolerant but needs protection from wind.

Waxflower: Jamesia americana Upright branches with heart-shaped leaves. Red Fall color.

Additional Resources

The Colorado Native Plant Society offers readers a list of local businesses where native shrubs can be purchased.

The Colorado State Forestry Service offers bulk purchase of native shrubs for large property owners. By bulk, I mean bundles of bare root shrubs or sold in 60 cubic inch tubes per species. Inventory is now limited as ordering began last November, but some great choices are still available.  The CSFS Nursery relies on cooperating agencies to promote and sell most of its seedlings to landowners in their respective regions. Seedling cooperators include CSU Extension, conservation districts and CSFS field offices


Amending The Soil Till It Is Workable

To commemorate Earth Day, we’re turning our attention to improving garden soil with this post from Steve Aegerter, Denver Master Gardener since 1999 and a first time contributor to the blog.

You don’t have to be a kid to enjoy digging in the dirt.

Gardeners do it all the time and it’s not just for fun and games. Rather, over a few seasons, digging in the dirt can substantially improve your garden’s performance. With a bit of work and some patience, you will have soil that is ideal for plant growth with a texture that is moist and crumbly like chocolate cake. But, no matter how delicious it appears, I don’t recommend eating it!

Here are answers to commonly asked questions about improving soil.

When is it safe to work the soil?

Great question. Disturbing, stomping, or digging in a wet garden can damage soil. The baseball test is an easy way to determine if soil can be worked safely. Here’s how it is done:

  • Take a soil sample by digging a few inches straight down.
  • Remove enough soil to form a tightly packed “baseball.”
  • Hold the ball waist-high, and drop it on a hard surface, such as a sidewalk.
  • If the ball falls apart, it is safe to dig in the soil.
  • If the ball stays glued together, the soil is too moist and should not be disturbed till it dries out.

What should I add to my soil?

The very best way to know how to improve your soil is to have it tested by Colorado State University’s Soil Testing Lab. The analysis provides detailed, easy-to-follow recommendations tailored to your soil ‘s composition and the plants you want to grow. For example, native plants prefer minimally amended soil (often not at all) while veggies prefer richer soil. Directions for submitting a soil sample can be found here. Each test costs thirty five dollars.

In lieu of a soil test, a general rule of thumb is to spade one to two inches of compost and well-broken up peat moss into the soil. Compost adds organic matter and breaks down the clay texture of soil and peat moss will lighten the soil, improve its texture, and increase moisture retention. If you elect to use a rototiller, proceed with caution as over tilling soil can damage the soil’s structure. For further reading on soil preparation and composition visit PlantTalkColorado #1605 on Soil Preparation and CSU GardenNotes #212 for an in depth look at soil composition.

What is double-digging?

Double-digging is a more labor-intensive soil preparation process that results in deeply amended, workable soil. It is particularly appropriate for new, non-native garden beds.

Here’s how to double-dig a four-foot-wide garden bed:

  • Spread one to two inches of soil amendment on top of the entire bed.
  • Starting on one end, remove a four-foot-wide, shovel-blade deep section of soil, creating a trench.
  • Place this soil in a wheel barrel.
  • Us a spade or garden fork to work one to two inches of additional amendments in the bottom of the trench. This is the “double-dig.”
  • Dig another shovel-deep section of soil next to the first trench.
  • Place the soil from this section atop the first trench.
  • Repeat the digging steps for the remainder of the bed.
  • The final section of the bed will be topped off by the soil in the wheel barrel.

Can soil be improved in the fall?

Yes, definitely. In autumn, spade a couple of inches of dead leaves into the soil followed by a second layer of leaves on top. During the winter, the leaves will decompose, adding valuable organic material into the soil.

Remember, you can order the best seeds from catalogs, or purchase amazing plants from the most popular nurseries, but they won’t produce a good harvest in poor soil. Use these techniques for amending soil and in a couple of years, your friends will envy your amazing garden!

So get out there, be a kid again, and start digging in the dirt.

Indoor Gardening with Microgreens

By Uli Klein
CSU Extension-Denver Master Gardener since 2019

Microgreens have been on the menus of high-end restaurants for years, and now you can grow them at home. Their colorful appearance and delicate flavors make them an attractive garnish to spruce up salads, soups, and sandwiches. Health-conscious consumers appreciate their high level of nutrients and add them to smoothies and protein shakes.

If you’ve never grown microgreens, now’s the time. For beginners, I recommend starting with some basic equipment and growing a few easy varieties. Then, after your first success, explore the many different tastes, colors, and textures that microgreens can provide.

Sprouts, Microgreens, Baby greens – What’s the difference?

Sprouts are grown in closed, humid conditions. They only need water, no soil or even sunlight, to grow. In general, sprouts take about 1 week to grow, and both the stems and seeds are edible. They add vitamins and a crunchy texture to recipes.

Microgreens are grown in soil, soil substitute, or on a hydroponic mat. Microgreens are easy to grow with light, air, and some ventilation. The risk of contamination with bacteria is negligible as long as they are handled properly and only healthy plants are consumed. Microgreens are typically harvested at the cotyledon or first leaf phase, but some varieties can be grown to the true leaf phase. Most take between 1 to 3 weeks to grow. Only the leaves and stems are eaten.

Baby Greens are smaller leafy plants compared to their mature counterparts and are grown in soil or a soil substitute, or they’re grown hydroponically. They are harvested before they are full grown, on average after 40-60 days and at 4-6 inches tall.

How to Grow Microgreens Indoors

All you need to grow microgreens are containers; soil, soil substitute or a soilless mix; and microgreen seeds.

Fill clean and sanitized plastic containers, like small blueberry containers or larger strawberry containers, with ½ to 1-inch of moist soil or other substrate such a coconut coir.

Select seeds that are specifically labeled for microgreen or sprouting use. The easiest and fastest-growing seed varieties include radish, arugula, kale, cress, broccoli, mustard, and Asian greens. Cilantro, basil, pea, and sunflower greens can be more difficult to grow. Avoid tomato, pepper, and eggplant seeds because these seedlings contain alkaloids, which are toxic for humans at high levels.

Sow seeds evenly and fairly thickly on top of the soil. If you’re planting microgreens in large quantities, a seed density calculator can help.

Gently tamp seeds down into the soil surface. Large seeds benefit from a light covering of soil; smaller seeds germinate faster by leaving them uncovered.

Place the seeded container on a tray, such as a 10 x 20-inch tray or plant saucer. Moisten the seeds with a gentle spraying at first, then water the container from the bottom tray to keep the soil moist, but not soggy. This method keeps the leaves and stems dry to avoid plant problems.

Some microgreen growers recommend the optional step of covering the seeded tray with another tray or dome for 1-to-3 days to help speed germination and to keep moisture in.

Microgreen seeds can grow on a windowsill with the available light from a window and at room temperatures between 60- and 75-degrees Fahrenheit.

Once the plants are around 1-inch tall, intermittent gentle horizontal airflow with a fan helps to keep plants healthy and strong.

Some of the microgreens are almost ready to harvest; more will be ready in another 7-to-10 days.

How to Harvest Microgreens

When plants are 2-inches tall, use scissors to cut the stems about ¼-inch above the soil level. Small and deep containers may make it difficult to cut the plants, so carefully lift the entire plant and soil complex out of the container to harvest. It can be messy if it breaks apart because the roots aren’t sufficiently interwoven with the soil.

The plants won’t regrow after harvesting, so the growing medium with the roots is best recycled by composting it. Clean and sanitize the containers and replant with a new batch of seeds to ensure a steady supply of microgreens.

Indoor Seed Starting for Beginning Gardeners

By Jessica Harvey
CSU Extension-Denver Master Gardener since 2020

Pepper plant starts with both cotyledons and first set of true leaves visible. Photo provided by Jessica Harvey.

We’ve all fallen prey to the allure of seed catalogs during the winter, with their bright photos and promises of plants to come. So what do you do after your seeds arrive?

Before you do anything, consider how much space you have to grow. The expression “your eyes are bigger than your stomach” can also be applied to buying seeds and finding places to plant them. After you’ve narrowed your planting choices, it’s time to get started.

Begin by deciding which flowers and veggies should be started indoors in early spring and which are better suited to direct sowing into your garden. Check seed packets for seed starting information or use a seed-starting guide.

You can grow in just about any type of container, whether it’s a leftover egg carton or a grow kit. The important thing is that it’s clean and free of potential fungi or bacteria. If you’re reusing trays, be sure to clean and rinse several times before using so there’s no residual disinfectant or soap.

Grow kits generally come with a bottom tray, cell tray and a dome. The cell tray will have slits or holes to allow water to be soaked up from the bottom tray. If you aren’t using a kit, you’ll need to create your own that fits the containers you’ll be using. A three-part system will be important as you get started to help bring those seeds out of dormancy.

There are number of inexpensive soil-less media options to choose from. If you want to use a soil-based starter just be sure it’s loose, fine in texture and has good drainage. Seeds need to be kept moist, but not sitting in water.

Once you have your containers ready and filled with your seed starting media, place a couple of seeds in each cell. Best practice is to make a small indent with your finger on the top of your media and lightly cover the seeds as you go. Always check seed packets for planting depth to keep from planting too deeply.

Record as you go. Draw a grid and write in each variety/plant to avoid playing a guessing game later. Note the date as well. If you know when you started, you can gauge when to start these same types of seeds again in future years based on your experience.

Mist or lightly spray the mixture atop your seeds, again moist but not wet. Don’t apply a stream of water or seeds will wash out of the cell. Add a thin layer of water to the under tray to start soaking up into the media. Keep water in that tray throughout the growing process. When your seedlings start to grow and send out roots, they will grow towards it.

Put the three-part system together and create a moist, humid environment to wake your seeds from their dormancy, then wait. Your seedlings will appreciate the humid environment under the dome.

Most seeds also like bottom heat as they get started, especially tomatoes and peppers. You can use a heat mat, but you can also place your container on an appliance or area that stays warm. Keep containers warm until seeds begin to sprout, then move them or turn off the heat mat. If you leave your seedlings exposed to that extra warmth for too long you run the risk of them stretching or getting leggy.

Once seedlings emerge, move them into the light and remove the dome cover. They may still enjoy that humid environment, but you don’t want them to start pushing against the dome. As they continue to grow, you’ll notice a first set of leaves called cotyledon. Don’t be fooled, the cotyledons are false leaves! They help seedlings start to photosynthesize, but they aren’t the true leaves of your plant. The cotyledons will eventually die as the actual leaves start to grow.

You can begin transplanting these plants into individual containers and soil-based media once the first true leaves develop. While transplanting, thin out the seedlings to give them room to grow without crowding. Depending on the seeds, you may have over sown and that cell may now be overrun. That’s okay! Just be sure not to let all those seedlings outcompete one another.


Gardening With Seasonal Allergies

There are an estimated thirty five million people in the United States who suffer with seasonal allergies. If you’re not affected, you likely know someone who is. For gardeners, pollen and molds are the most common allergens.

Wind-Pollinated versus Animal-Pollinated Plants

Pollen is a powdery substance from the male part of a flower (stamen) or cone which can fertilize the female ovule. Pollen travels by animals, insects, or wind.

Wind-pollinated (anemophilous) trees, shrubs, perennials, and weeds produce  airborne, toxic pollen. Common characteristics of these plants include small, inconspicuous, often petal-less flowers, which generally lack bright colors and have little scent or nectar.  Examples include Cottonwood trees, Gambel oak, Rocky Mountain Maple, Ragweed, Dandelion, and turf grasses. A comprehensive seasonal list of Denver’s highly allergic plants can be found here.

According to the U.S. Forest Service, wind pollinated plants “release billions of pollen grains into the air so that a lucky few will hit their targets.”

By contrast, animal or insect-pollinated plants are not usually responsible for pollen allergies. If a bee or butterfly feasts on the plant’s pollen, it is less likely to be the cause your watery, itchy eyes. Flashier and generally more colorful, these plants produce pollen which is stickier and contain large, heavier particles. The “stickiness” is what helps the animal transport pollen from one plant to another.

Mold Allergens

Molds are found in partially decomposed compost piles, dried leaves, branches and bark mulches, are present nearly year round in Colorado and can be very toxic.  Spring clean up is prime mold allergy season.

Climate Change and Allergy Season

William Anderegg, a researcher from the University of Utah found “…a strong link between warmer weather and pollen seasons provides a crystal-clear example of how climate change is affecting people’s health across the United States.” Further, his study concluded that as compared to 1990, the current pollen season starts twenty days earlier, lasts ten days longer and contains twenty one percent more pollen.

Tips for Gardening with Allergies

Here are a few things to consider to manage allergies while gardening:

  • Mow lawns short so turf does not set seed or have someone else do the mowing. 
  • Replace turf with groundcovers or suitable plants.
  • Substitute rock mulch for bark mulch, which can harbor mold.
  • Reduce exposure to a compost bin – mold can be present in unfinished compost.
  • Pay attention to local pollen counts.
  • Repurpose your mask. It will keep pollen from your nose and mouth.
  • Cover up – hats, long sleeves, glasses also help.
  • Change clothes when you come inside and shower promptly.

Additional Reading

National Jewish Hospital, Pollen Count for Denver, Colorado

As Climate Change Extends Allergy Season, Pollen Travels

PlantTalk Colorado #1758, Cottonwood Trees

Harvard University. Allergies? Tips to Minimize Your Mold Exposure

Written by Linda McDonnell, Denver County Master Gardener since 2013

Wild About Natives: Native Trees for Colorado

In response to our reader survey, the Denver Gardeners blog is adding a monthly feature on native plants by CSU Extension-Denver Master Gardener Kathy Roth. Kathy is an experienced Master Gardener who has researched, planted and maintained native landscapes and gardens since 1995. She currently grows three native trees in pots on a downtown condo balcony.

By Kathy Roth
CSU Extension-Denver Master Gardener since 2018

Spring officially arrived March 20th…but we can easily remember the piercing winds and bountiful snowfall of just a few weeks ago! Unfortunately, many homeowners experienced tree damage and/or loss due to late Spring (or last year’s early Fall) snowfalls and are now looking to replace those trees. This is the perfect time to consider a native tree choice.

What exactly is a “native tree” you ask? According to the USDA, a Native Plant (or tree) is “A plant that is a part of the balance of nature that has developed over hundreds or thousands of years in a particular region or ecosystem. Only plants found in this country before European settlement are considered to be native to the United States.”

Native plants and trees are important because they are adapted to our climate, soil and environmental conditions. They require less maintenance, watering, fertilization and pruning and are affected by few insect or disease problems. Landscaping with native plants helps maintain biodiversity that is often lost to land development. When non-native plants are introduced, they may threaten our ecosystems as they often out-compete natives. These invaders may cause many birds, mammals and insects to lose their food source, causing Colorado’s wildlife residents to become scarce and threatened.

Some non-native trees have brittle wood that can split and/or have branches that ‘peel’ down the trunk like a banana if wet snow collects in the crotch where limbs attach to the trunk. In Springtime, many non-natives leaf out too early and can be ‘caught out’ by our heavy, wet late Spring snows that collect on leaves and whose weight pulls, breaking branches and limbs. Extreme temperature fluctuations, such as those we experience in the foothills areas, also adversely affect many non-native trees.

A myriad of free online resources on various garden topics are available to the public on the Colorado Extension website. One such resource is Plant Talk. #1710 gives a brief overview of some native tree options. Cheerful evergreens splash our brown winter landscapes with much needed color and their needles are flexible in winter winds, resisting snow damage.

Large evergreen tree suggestions that grow to about 45’ or higher when mature include:

  • Our state tree the Colorado Blue Spruce (attractive horizontal branching and high wildlife value to both song & ground birds – even grouse and small browsers)
  • The Limber Pine (large ornamental cones)
  • Southwestern White Pine (bark has an interesting scaly texture when mature)
  • Ponderosa Pine (my favorite due to the bark turning cinnamon color with age and giving off a vanilla fragrance on warm days – plus it tolerates our alkaline soil well)
  • Douglas Fir (fast growing with medium to dark green needles and a classic pyramidal shape; provides browse for deer & elk)
  • White Fir (conical shaped, drought & heat resistant with soft blue green needles but prefers protection from wind)

If your property is not large enough to accommodate the massive specimens listed above, smaller evergreens whose mature height varies from 10’ – 45’ include:

  • Pinyon (compact & bushy)
  • Bristlecone Pine (unusual artistic branches have bottlebrush appearance)
  • Rocky Mountain Juniper (produces berry-like fruit that is an important food for small mammals and birds)
  • Utah Juniper (also produces food for wildlife in the form of large, grayish-blue berry-like fruits)

If you are looking for deciduous trees, please consider:

Hot Wings: Breath-taking scarlet red samaras on a Tatarian Maple photo provided by Plant Select
  • Big Tooth Maple (provides orange-red Fall color)
  • Gambel or “Scrub” Oak (shrub-like growth whose leaves are red, orange, yellow or brown in fall and its acorns provide excellent wildlife food)
  • My personal favorite originates from the Plant Select Program called Hot Wings Tatarian Maple (Acer tataricum GarAnn’). Reasons include unique red samaras (“propellers” or “helicopters”), the leaves’ spectacular Fall color and that this tree thrives in our alkaline soils rather than struggles with iron chlorosis like non-native maples.

CSU also provides Fact Sheets specific to Native Colorado tree choices. Dr. James Klett from CSU wrote “Native Trees for Colorado Landscapes.” This comprehensive Fact Sheet provides a table that groups tree choices by size, whether evergreen or deciduous, their moisture requirements, and brief descriptions or comments about each tree selection.

The Colorado Native Plant Society offers readers a list of local businesses where native trees can be purchased.

The Colorado State Forestry Service also offers bulk purchase of tree seedlings for large property owners. By bulk, I mean bundles of 20-30 trees per species. Inventory may be limited as ordering begins in November. The CSFS Nursery relies on cooperating agencies to promote and sell most of its seedlings to landowners in their respective regions. Seedling cooperators include CSU Extension, conservation districts and CSFS field offices.

Lastly, a visit to Denver Botanic Gardens will enable you to see many native trees and plants growing “in-situ” or in place. The garden’s Native Plant Collection consists of over 700 species belonging to 323 genera. To focus on locating & viewing their Native Trees, simply use their Navigator.


Survey Shows Need for More Volunteers

We’d like to say a big Thank You to the 73 blog readers who took time to respond with such thoughtful feedback to our reader survey!

We appreciated every comment, every suggestion and every article idea. As we celebrate the 6-year anniversary of the blog, we’re keeping in mind two key takeaways from the survey:

First, readers enjoy reading the blog. 90% of respondents reported being satisfied or highly satisfied with the content.

Second, the blog team needs more help
. We received so many terrific suggestions for future blog content that we need a few more Master Gardener volunteers to lend a hand.

The CSU Extension-Denver blog is one piece of our social media presence and an important part of our Master Gardener outreach and educational efforts.

In fact, when the number of subscribers to the blog (300) was compared to the Denver Master Gardener roster, approximately 85% are not active Master Gardeners, according to Linda McDonnell, who dug deep into the numbers. That suggests our blog is reaching, encouraging and educating the general gardening community.

Join the Blog Team
Please consider volunteering – we have many opportunities that can be tailored to fit your skills and interests. You don’t need to be tech savvy or even a great writer because the team can help every step of the way from editing to posting and finding photos.

All you need to join the team is the willingness to help other gardeners get more from their gardening experience. Plus every hour spent on the blog counts toward your volunteer service for 2021.

Two current opportunities include:
Monthly gardening to-do lists. This would be an ongoing volunteer opportunity to compile a month-by-month calendar of gardening tasks.
CSU Extension topics, like the most frequently asked questions we get from the community. Researching and writing about those questions would be an easy way to get involved with the blog!

If you’d like more information on volunteering for the blog team, please get in touch with Merrill at the CSU Extension-Denver office 720-913-5272.

More Opportunities for the Future
One of our main goals is to continue to grow our readership with the content readers want. Overwhelmingly readers asked for more how-to gardening content in specific topic areas. Let us know if you’re interested in writing on any of these topics:

• Native plants
• Landscaping topics, especially drought-friendly landscaping and alternatives to lawns
• Permaculture and sustainability topics; water conservation
• Veggie gardening for our area
• In-depth and timely insect pest information
• Plants for shade
• Houseplant tips
• Growing small fruits
• Choosing trees
• Gardening in a changing climate
• Small-space gardening for apartments, condos, community gardens
• Garden spotlights: pollinator gardens, Master Gardener projects (before and after)

Help Promote the Blog
One way all readers can help the blog reach a wider audience is by forwarding each new blog post email to your gardening friends.

Another way is to encourage other gardeners to sign up to follow the blog by email in the box on the upper right side of the Denver Gardeners website

Three Book Winners Selected
Everyone who completed the survey and provided their contact information was part of a special book drawing. The three names selected at random to receive a copy of Plant Partners by Jessica Walliser include:

• April M.
• Cathy R.
• Margot T.

By Jodi Torpey
CSU Extension Master Gardener since 2005
Image by Pixabay

Growing Shamrocks

Thank you to everyone who responded to our Reader Survey. We’ll be sharing an overview of responses shortly, but for now, here’s a seasonal post suggested by a reader.

March brings longer days, the promise of spring, and shamrock plants to commemorate Saint Patrick’s day. There are many species of shamrocks including Oxalis acetosella and Oxalis deppi. All are prized for their three triangular leaflet foliage and dainty white or pink flowers. This holiday-themed plant, believed by many to bring an abundance of good luck, can be a long-term addition to a houseplant collection.

Here are some pointers for appreciating and successfully growing shamrock plants:

  • Actively growing plants benefit from a bright setting – a sunny window or strong indirect light is ideal. Daytime temperatures of about 70 degrees and evening temperatures about 10 degrees cooler, moist soil and light fertilization are preferred. Due to a shallow root system, repotting is seldom needed.
  • Shamrocks are nyctinastic – meaning that the leaves will fold in response to lack of daylight and unfurl when bright light returns.
  • The shamrock plant is a cluster of small bulbs, and like many bulbs, need a period of dormancy. The plant is starting this period when leaves yellow and go limp. Many a shamrock plant has probably been mistaken for dead at this stage! In approximately four to six weeks, new growth will emerge from the crown.
  • Pets and shamrocks may not mix. My cat is usually indifferent to plants but can not resist mowing down a shamrock. While he has not gotten ill from this mischief, it can be highly toxic to cats and dogs if enough is ingested.
  • Shamrock and clover are terms that are used interchangeably.

    White clover found in the lawn (Trifolium repens) is not related to the houseplant, although both have the characteristic three-leaflet foliage. Lawn clover, while often the bane of grass enthusiast’s existence, is gaining interest as a turf alternative or garden cover crop. A beneficial property of white clover is its ability to improve the soil by adding or “fixing” nitrogen in the soil.  Perhaps in this way, clover in the lawn or garden is lucky, too!


PlantTalk Colorado #1354, Shamrocks as Houseplants

PlantTalk Colorado #1542 White Clover in Lawns

Written by Linda McDonnell, Denver Master Gardener since 2013