When & How to Use Compost as Mulch (For Best Results)

The right time and place to use compost will make all the difference in thriving gardens. If you’re looking for the right way to use compost as mulch, you’ll need to know how and what may result.

Spreading an even four to six inches of compost onto your soil will have similar effects as mulch. Re-apply compost halfway through the growing season to prevent weeds from growing from the first layer of compost.

In our gardens we’ve tried various mulches and composts, both homemade and purchased composts, to suppress weeds in our vegetable gardens. After all those experiments, we’re able to shed some light on what works and doesn’t, in various types of places.

Not only will we share what we know, but we also asked worldwide gardeners about when they apply compost or mulch so we can provide you with well-rounded information.

Below:

  • You’ll learn all the ways using compost as mulch makes more or less sense for various garden styles and…
  • See the results of an interesting poll asking worldwide gardeners; when they apply compost or mulch and where they live. The detailed results I received include the most popular month for amending a garden!

Can compost be used as mulch?

Pros and cons exist in everything. Compost as mulch is a perfect solution for most vegetable gardeners, but not for every garden type.

Compost can be used in place of mulch, but amendment is its primary purpose. Building with organic material is always better than allowing depletion, and leaving mulch off the surface has practical benefits. Since compost is finer and darker than your typical mulch, it warms quicker in spring.

Mulch is usually avoided in vegetable gardens because fresh mulch has yet to break down. Breakdown processes require energy and building blocks. Carbon-heavy mulches serve as energy for microorganisms and they expend this energy to build cells from nitrogen sources. Nitrogen is then tied up and used for breaking down mulch instead of growing nitrogen-loving crops.

Adding compost instead of mulch is definitely Ideal for high-nitrogen annual crops such as brassicas, onions, leeks, and greens in general. These plants also tend to grow foliage quickly and provide shade to their own soil so the next paragraph quickly becomes irrelevant!

The caveat of not protecting compost with a topping of mulch is life loss —An important matter to regenerative gardeners who intend to grow more permanent crops or non-permanent crops in less biologically disruptive ways. Compost is basically soil without rock content and is teeming with life. Microorganisms can’t live on the exposed surface and as deep as it dries.

The reason this isn’t a deal-breaker from using compost instead of mulch is that the new compost will foster an environment beneath for microorganisms to thrive. Only the fresh compost—at least the surface of it—may become inhospitable. Either way, to mulch or not, is up to the extent that you care to maintain.

The easiest, most regenerative way to grow annual crops with compost employs ground cover plants. If you’d rather preserve the life within your compost; apply it, and seed it immediately with ground cover crops such as clover.

Perennial settings benefit most from mulch material. Weeds grow too easily in compost for such passive areas. In a food forest, for example, you’d lay fresh mulch each year to keep weeds smothered, and competition absent. Then you’d forget about it with no need to do much else.

Flat settings allow available nutrients in fresh compost to leech deeper with every rainfall.

On slopes, erosion may become an issue after periods of drought. Finished compost that is fine as the soil will dry, crust, and resist water. The resistance will cause the force of water to cut through and erode downhill.

Secondary to established roots, mulch prevents soil erosion because it doesn’t crust over when dry and the large particles catch water.

The happy medium is unfinished compost if you don’t want to use mulch on a slope. It has a particle size between finished compost and mulch.

Unfinished compost on a slope can prevent the surface from drying too quickly. Even when it does dry; crusting doesn’t occur and larger particle sizes will catch more water allowing it to moisten the ground more quickly.

Without established roots, erosion will always occur on slopes to some degree.

This article was originally published on foodforestliving.com. If it is now published on any other site, it was done without permission from the copyright owner.

What is the best compost for mulching?

Applying compost for the purpose of amending or mulching (or both) have the same goals. Ultimately, they both build soil.

A finished or near-finished balanced compost is the best for mulching. Adequate macro and micronutrient content come from a variety of materials. Proper carbon-to-nitrogen ratios are required for organic matter to decompose into a rich soil topper.

Can I use multipurpose compost as mulch?

Multipurpose compost can be used as mulch, but won’t act the same as mulch. Using compost as mulch is often the more practical choice for growing annuals. Compost as mulch makes sense for perennial areas if ground cover crops are seeded right after compost application.

Homemade or store-bought compost brands can be applied the same way.

When should I add compost to my vegetable garden?

I wondered if there was a “best time” of year to apply compost to a vegetable garden. Even wondering if it was different around the world! To find out what everyone else is doing and why; I polled a worldwide set of gardeners to find out what month they spread their compost or mulch and where they live.

It turns out that…

April and October are the most popular months when gardeners apply compost or mulch to any garden (based on a worldwide poll). Every gardener has reasons for spreading compost in the spring or fall. And some encourage you to work in the compost any time of year, whenever an opportunity strikes.

Based on 150 votes, below are the reasons you should apply compost when.

We asked everyday gardeners when they apply compost/mulch:

Hundreds answered, and we included several responses (by month) below.

February: 7 gardeners voted they compost or mulch in February.

  • Sandra from Santa Rosa, CA., and one from central CA say they mulch in February because they “don’t have a real winter.” Their winter is more like what people call fall.
  • Julia from Indiana, use well-matured manure for compost. Applied in the fall usually but in February this year due to health issues.

March: 14 gardeners voted they compost or mulch in March.

  • Bob from Seattle, WA applies compost in spring and fall “depending on the crop.” He always has something planted in at least one bed on a year-round basis. Some are resting while others are in use. The beds that received unfinished compost in March are currently growing greens, cabbages, broccoli, carrots, and onions that are enjoyed well into winter and beyond winter.
  • Jesse from Northeast Ohio applies homemade compost put on in November and aged cow manure in March. She usually mulches the garden beds in the fall, but this year waiting until early spring next year. “It’s supposed to be a really cold winter. . . maybe fewer bugs will survive without the mulch. We will mulch the strawberries, asparagus & rhubarb. Our garlic is already mulched.”

April: 33 gardeners voted they compost or mulch in April.

  • Amanda from Rochester, NY
  • Meagan from southern Ontario in spring or fall. “When temps are above zero and ground is workable.”
  • Marije from Netherlands, Europe. “I prepare my garden before I can plant out in May.”
  • Silla is from the rocky mountains in Canada. “We have to wait until April to start our garden in June.”
  • Jennifer from Southern BC, zone 5a. They compost in both spring and fall if they have enough. They use “lots of leaves in the Fall too” for mulching.
  • Heather, when living in BC Canada; they apply “spring manure and compost was as soon as the snow melted in March.” They do it all again as plants are cleared between September and November depending on the weather. . . continued

May: 10 gardeners voted they compost or mulch in May.

  • Continued. . . Now she is in Alberta. “So spring mulch will be in May” and then right before the snow by October.
  • Adam from southern Ontario Canada composts “in the spring mostly but as needed throughout the season.”
  • Jen from Minnesota applies compost in May, June, and July when planting the veggie garden. Then they do the flower beds in September.

September: 7 gardeners voted they compost or mulch in September.

  • Suzannah from the southern hemisphere in Sept/Oct (which is spring). Says she applies compost in spring because she’s already digging the garden over so it makes sense to do it all at once. “I haven’t even started this year, just too much catch-up everywhere else.”
  • Frances from Eastern England UK. Zone 8b/9a. Mulches in the autumn which is the end of September and October in their area. They also apply compost again in March/April prior to planting.

October: 32 gardeners voted they compost or mulch in October.

  • Dustin from Klamath Falls, Oregon. He applies unfinished compost in late October because it takes several months for microorganisms to break down plant materials into usable nutrients. “So I always fall incorporate.”

November: 6 gardeners voted they compost or mulch in November.

  • Joy from NE Oregon says they lay most mulch in the fall which is early November. In late spring she uses last year’s composted kitchen waste/yard debris and uses spent chicken straw to fertilize the mulch.
  • Sassafras Farm from Arkansas planted and mulched their garlic in November and “have yet to put chicken litter on fruit trees and shrubs” but will be doing so shortly.
  • Sylvia from Northern California coast uses compost as mulch in mid-November. “As I grow year round, I don’t mulch necessarily at all.”
  • Bob from Seattle, WA who does March mulching—for winter beds—also applies it in November, but for the spring/summer beds. Unfinished compost is added to the beds before winter so they are ready for spring planting.

December: 4 gardeners voted they compost or mulch in December.

  • GiGi in Atlanta says they have mild winters so they amend their garden by the end of December. “My broccoli and Brussels and lettuces are still going crazy.”

Summary

Many of the gardeners voted for multiple spring and fall months, and 2 gardeners voted for spring through summer months. A few gardeners without “a real winter” selected the “winter” months.

Finally, 23 gardeners voted that they apply compost and mulch any time of the year, as needed, or any time there is a blank space opportunity.

Rodney from Tasmania Australia. They mulch using aged compost any time of year as needed. “Mulch that isn’t broken down robs the soil of nitrogen as it breaks down.”

Adamandia from Massachusetts says it “depends on the crop.” For example, she mulched garlic in the late fall after she plants them in zone 7A.

Reasons when to compost summary

  1. Prior to planting – any time of year
  2. Apply small amounts year-round as needed
  3. Before the ground is frozen for winter
  4. As the last harvest from each bed is taken for the season
  5. When physically capable
  6. Sprinkled on top of freshly sown seeds

Reasons when to mulch summary

  1. For warm climates that can grow year-round —mulch is generally in the spring.
  2. Before the rains in spring
  3. Before the summer heat
  4. Before the spring crops are started
  5. When plants are removed and soil is left to rest
  6. When leaves are available in the fall
  7. Lightly after planting seedlings or broadcasting seeds
  8. Fall; getting ready for winter for a blanket during cold, snowy winters
  9. Spring; when things are sprouted enough they won’t be buried in the mulch
  10. Summer; when the spring mulch is broken down and weeds are starting to pop through

Do you mix compost into soil or put on top?

Our results weren’t different between mixing versus not mixing compost into the soil when applying it to the surface. So we concluded that less is more.

Apply compost on top of the soil without mixing. Rain amalgamates compost with soil naturally. Plant growth is not affected negatively by leaving the soil alone. Since the rain does the job; manually mixing mediums is unnecessary. Stirring the soil with tools will disturb and harm microorganisms.

This answer is also clear when you look at the forest. A forest doesn’t require humans to manually mix the soil in order to grow plant life. Microorganisms and rainfall will turn the mediums as needed.

A forest floor is built from leaves and wood falling on top of the unfinished composted leaves and wood. Beneath the unfinished compost, is finished compost. From rain, temperature heaving, and wind; rock even amalgamates into the naturally built compost, and altogether rich soil is created over time.

What goes first compost or mulch?

Forests demonstrate functional systems that rely on gradual compost and mulch. Compost is an “older” material than mulch therefore is always applied before mulch.

Compost is always applied before mulch because organisms that further break down compost require protection. Mulch doesn’t need protection because it is the protector. As the mulch ages, top it with fresh mulch, and microorganisms can move into the old mulch to make new compost, safe from harsh elements.

You can also do this topping technique with compost rather than mulch if you prefer less work when growing annuals.

When growing perennials, using mulch is less work than using compost for more permanent weed suppression.

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Rachelle

While Rachelle's hands are clean for the keyboard, she enjoys writing and designing creative content and resources. You will most likely find her outside planting a cabbage, foraging berries for breakfast, and collecting herbs for year-round tea or making food.

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