When to Put What Under Mulch (If Anything)

Many types of materials can be put down before mulching, but it isn’t always necessary. Mulch can be one with the soil too! Your decision depends on the objective and needs of the area you’re mulching.

Does the mulch need help fixing a problem? Must anything go under mulch?

Appropriate materials go under mulch if it serves a purpose. To suppress established weeds: put an organic sheet material under mulch. To nourish weed-free soil: apply compost and protect it with mulch. To top up a mushroom bed: nothing needs to go under the fresh mulch.

Mixing and matching the wrong choice for your situation can lead to more problems than you intended. For example, fresh mulch applied directly to an annual bed may tie up the nutrients that vegetables require.

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 should I put down before mulching?

Discovering all your under-mulch options means you’ll learn what to use and when.

Compost, organic sheet mulch, nothing, and water are all good things to put under mulch. The best option relies on the situation. Plastic and landscape fabric don’t serve well beneath mulch in general.

See table for material and situation details:

Materials to put under mulchWhen to put what before mulching
CompostAny annual or perennial garden.
Plastic tarpNo permanent situation calls for laying plastic beneath mulch
CardboardSheets for weed suppression: new perennial beds or pathways in annual areas
Landscape fabricNo situation calls for landscape fabric beneath mulch
WaterBefore and after laying mulch is fine but not always necessary
NothingTopping up last year’s mulch for perennial areas
What to put under your mulch and when.

What can I put under mulch to keep weeds down?

Applying shredded mulch onto established weeds won’t get you very far in keeping them down. Established weeds need total light deprivation to die and discontinue growth—a good scenario to put a useful material under your mulch.

Any sheet material such as cardboard, newspaper, or paper leaf bags can be used to deprive established weeds. Persistent weeds should be removed before laying any sheet mulch material to avoid brewing big sneaky root system survivors beneath.

Weeds will stay down for as many seasons as you maintain your mulch. To continue weed suppression, apply more mulch every year.

Related post: What material is the best for sheet mulching?

Do you put mulch on top of compost?

Mulch on top of compost makes more or less sense in various settings.

In general, mulch on top of fresh compost is ideal for protecting active life from the drying sun. It’s practical to apply mulch on top of the compost in perennial settings. Compost piles can be protected with a tarp while they are not in use.

No matter where compost is placed, it will benefit from the protection of mulch. But mulch isn’t always a practical choice to include.

Can you just put compost on top of soil?

When mulch isn’t a practical option, don’t apply it! Vegetable gardens are an example where mulch isn’t always realistic, but they still need an application of compost to thrive.

You can apply compost to annual beds without mulching them. A good layer of compost is better than nothing. Mulch is often in the way when applied to beds that grow any annual plants.

Unless we are planting garlic, it isn’t usually a practical choice to put mulch on top. Garlic easily pushes through 2-4 inches of shredded leaves in spring while keeping weed seeds from ever germinating.

Mulch for garlic works but would hinder all your vegetable seeds from germinating. To transplant seedlings, any mulch would need to be removed for efficient digging and burying, perhaps to put all the mulch back on top if that’s your thing.

Ideally, annual foliage would have been nourished enough to grow so lush they shade their own soil for summer. All plants including vegetables benefit from cool soil. Cool soil prevents bolting. So, mulch after planting may make sense for brassicas unless you have them beneath a shade bug net.

In your everyday vegetable garden, dark-colored compost is applied and lightly raked into the soil surface every year. The dark color and fine particles of compost quickly warm soil in spring. If you were to cover your compost with mulch, the opposite would be true.

Compost is usually dark and rich while mulch is neutral in color. Coloring and material densities change the rate of soil warming in spring. Mulch particles are larger than compost so they take longer to change temperature and don’t allow light through.

In climates with shorter growing seasons, more time is always a need! So it makes complete sense not to mulch a vegetable garden.

Perennials are hardy to your environment and don’t need warm soil to grow. They benefit from cooler soil throughout the season since foliage has no option! So while you can just apply compost without mulch, you may want mulch in some circumstances.

If you’re short on compost, you don’t need to apply compost to perennials. In our experience, perennials are happy either way. Eventually, they will reap the benefits of mulch as it composts into rich bio-available soil on the spot.

Should I water the ground before mulch?

Unless prized plants are thirsty, drenching the ground before mulching isn’t necessary. Watering before you put mulch down ensures moisture is immediately adequate in the soil. After mulching, you can water less frequently. It always helps to settle mulch by watering it after you’ve applied it.

If the ground already has moisture there is no need to water it.

Should I put plastic down under mulch?

Plastic under mulch may seem like a perfect idea to banish weeds forever. But permanently burying plastic beneath a good-looking mulch doesn’t really solve problems productively.

Plastic should not go under mulch as a permanent solution. For weed management, it’s best to use organic sheet mulch permanently or plastic tarps temporarily. This way, water absorbs instead of repels, and nutrients are included instead of isolated.

Unless you plan to slither a drip line to every plant, plastic will certainly deprive your garden of water.

Gardeners who line the ground with plastic don’t typically cover it with mulch. The plastic is the “mulch,” the weed suppressor.

In the case that you do lay black plastic as a weed suppressor . . . because it so happens that you have a drip line ready to weave . . . then consider that you do apply mulch on top of the plastic. Otherwise, your soil will bake under the black if it isn’t cooled by protective neutral tones.

Learn more: What is Sheet Mulching? 7 Ways to Do it (and When)


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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