Selecting The Best Mulch For Your Plants

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

Canva.com

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. Pixabay.com

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

Gulley Greenhouse.com

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. Canva.com

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!

Blessed Bee, Thy Name

Last week I attended a bee info session with Thaddeus Gourd, Director of Extension for Adams County to introduce new-bees to Dat Buzz Lyfe (I can’t believe this hashtag hasn’t been acculturated into the lexicon). Thad walked us through the bees we may encounter locally, how they got here, some typical and atypical behaviors, as well as a truly charming attempt at convincing me to bring bees to my own yard, regardless of my wife’s severe allergy, as he shows us his son bare-handing his GoPro at the bottom of a brand new bee abode. The bee community, it turns out, is pretty righteous. They are passionate about the bees livelihoods and are nearly involuntarily bursting with facts and love and recruitment strategies. As far as I can tell (and I’m pretty far), not only are bee keep-have-and-lovers informed of the goings-on of the world around them, they are also deeply involved in their communities with the idealism that we still stand a chance. 

One of my favorite parts of preparing for this post was reveling in how smitten everyone who writes, studies, or just enjoys, bees cannot help themselves to the low hanging fruit of the ever-accessible bee puns. I won’t go so far as to say it’s obligatory to at least dabble in the punny when writing about bees, but it’s pretty darn close (how’d I do?). 

To my surprise, North America has no native honey bees that produce large amounts of honey, and the bees we have working for us now were imported (intentionally and accidentally) by European colonizers. The European honey bees are typically docile and too busy to be bothered by folks approaching or tending to the hive-unless of course, the alarm is sounded and whatever intentions the intruder has are being interpreted as a threat, which apparently smells a bit like banana. File this under Lessons I hope never to encounter, and yet, how interesting! 

If you do happen to get stung, Thad informed us that the venom sack dislodges from the honey bee (essentially causing it to bleed to death, major bummer) and will continue pumping venom for another minute or so after the initial sting. To stop this, simply scrape the stinger from the entry point with a credit card or fingernail. DO NOT try and pluck it with your fingers or tweezers–this just pumps all the venom directly into the wound all at once. Expect the site to be a bit itchy after the initial shock and scramble settles, and write it off as an ouch! and a thank you for your service.

Of course, a small sting is literally nothing compared to the plight the bees face. Documentaries and campaigns are beleaguering (the opportunities for bee-utifying this entire post are just too much) the fate of our planet, and news reports of the extents of human willpower and reliance on the honey makers to keep the decline in bee population discussions plentiful. The main threats include loss of habitat, diseases and mites, pesticides, and climate change. 

As lovers of the living, albeit animal or vegetable, pesticide-speak can draw that line as firmly in the sand like many of our other hot button political issues. Be ye not afraid, comrades. We don’t have to go to the polls with this one, but we do have to follow the law (cue that GBU soundtrack). Treating plants–weeds included–with pesticides (neonicotinoids) while the plant is flowering transfers the chemicals into the nectar, and the feasting bees bring the toxins back to the hive. Truly, this seemingly innocuous move one time could kill an entire hive. Always read the labels, folks. Take your time and educate yourself on all the possible management strategies before grabbing the glyphosate. 

We are inundated with problems and presented with conveniently packaged solutions. We have come to a place that is moving so quickly that it’s too easy to keep in motion and miss the very real consequences each step incurs along the way. Unfortunately for bees, they are getting caught in our wake of rapidity. How can you take one extra breath, second, or step to consider your impact?

For those with a burgeoning interest in the apiary, one great way to check yourself is to plug into a community of other beekeepers/havers/enthusiasts. From what Thad was telling us, many organizations and groups are looking to help you get started, problem solve, or just ponder the wondrous life of bees. CSU Extension is an excellent resource for research and education on bees; they are continuing to compare hive designs to determine which work best for Colorado. There are also lots of beekeeper mentor programs, beekeeper associations, and even folks who you can hire to set-up and care for a hive on your own property. These folks have lots of experience and want to propagate more interest in beekeeping by mentoring and sharing. Getting into bees is definitely not something to go at alone or from a quick study. Taking risks is part of beekeeping, why not expand yourself right at the start by making new connections and community building?

By McKenna Hynes

Apprentice Colorado Master Gardener since January 2019