Mulch has been called the gardener’s friend—and for good reason. In winter, mulch protects bare soil, prevents erosion, and protects plants. In spring, mulch locks in moisture, suppresses weeds, and feeds the soil. Learn how to mulch, when to mulch, and about the many different types of mulch to use in your garden.
Mulching is a fundamental part of gardening to plants looking beautiful and productive through the year. If you don’t already know how to mulch, it’s important to learn when to mulch, the right depth for mulch, and the right type of mulch.
What Is Mulch?
At its simplest, mulch is any material that covers the soil’s surface. In nature, mulch is simply fallen leaves and plant debris. In the garden, mulch can also include compost, wood chips, rotted manure, cardboard, or even seaweed.
It’s only recently that we’ve come to appreciate mulch’s sustainable and ecological benefits. Done correctly, mulching feeds our soil’s living microorganisms with nutrients and the waste from these tiny microbes creates healthier soil structure for plants, limiting compaction.
Benefits of Mulching
- Reduces weed growth by keeping light from reaching the soil surface.
- Reduces water loss from the soil surface, which helps maintain soil moisture.
- Moderates soil temperatures, keeping it warmer on cold nights and cooler on hot days.
- Protects bare soil, reducing erosion and soil compaction.
- Protects plants from the harsh conditions of winter freezes, thaws, and winds.
There are many other benefits of mulch:
- In winter, soil under mulch will be warmer than unprotected soil. This protects plants from the cycle of freezing and thawing (which can heave them out of the ground).
- Prevents crusting of the soil surface. Water moves more readily into soil covered with mulch instead of running off.
- Keeps soil from splashing onto leaves; keeping soil off leaves reduces the chance of plants getting fungal and bacterial diseases.
- Breaks down and feeds the soil (if organic mulch).
- Improves the structure of clay soils and the moisture-holding capacity of sandy soils.
- Slowly increases soil fertility (if organic) and may make micronutrients already in the soil more available.
- Warms the soil in spring, allowing the gardener to plant days or weeks before the soil would normally be ready.
- Keeps plants clean and off the ground, especially tomatoes and melons, to avoid plant disease.
- Limits the chance of damaging trees’ trunks when mulch is placed around them instead of grass.
- Improves plant health and growth (due to fewer weeds and more consistent moisture and soil temperature).
- Makes gardens “spiffed up” and attractive, giving a uniform appearance and rhythm to garden design.
Disadvantages of Mulching
Although using mulch has many benefits, in some cases, its use can be detrimental to the garden:
- TOO much mulch (a layer more than 3 inches deep) can bury and suffocate plants; water and oxygen can’t reach the roots. A layer of 2 to 3 inches of mulch is ample. Do NOT overmulch.
- Mulch can contribute to rotting bark if piled up around the trunks of trees and shrubs. Keep mulch 6 to 12 inches away from the base of woody plants. No more “volcano” mulching around trees! Keeping mulch away from the trunk discourages wood-boring insects, gnawing rodents, and decay.
- Mulch near plant stems is the perfect place for slugs, snails, tunneling rodents, and more pests to reside. Sprinkle wood ashes or diatomaceous earth around the base of precious plants to keep the slugs and snails at bay.
- Mulch can bake your plants with excess heat in midsummer if not done properly. (See more below.)
- Light-colored, wood-based mulches, like sawdust or fresh wood chips, can steal nitrogen from the soil as they break down. Counter this effect by adding a nitrogen-rich fertilizer, such as soybean meal, alfalfa, or cottonseed meal, to the mulch. (Learn more about soil amendments.)
How Much Mulch Is Needed?
With most organic mulches, a layer of 2 to 3 inches is plenty. The finer the material, the thinner the layer needed.
Inorganic mulch is often more shallow. For example, a mulch of small stones usually only needs to be an inch deep.
If You Want Mulch This Deep… | …You Will Need This Much Mulch to Cover 100 Square Feet |
---|---|
2 inches | 18 cubic feet |
3 inches | 27 cubic feet |
1 cubic yard = 27 cubic feet
Dry mulches—including sawdust, woodchips, peat moss, and dry straw—can be a fire hazard. Keep them away from buildings to be on the safe side.
Types of Mulch
The ideal mulch should be dense enough to block weed growth but light and open enough to allow water and air to reach the soil. Factors to consider when purchasing mulch are cost, availability, ease of application, and what it looks like in the garden. There are lots of materials of various colors and textures to choose from.
Both organic and inorganic mulches can be used effectively in the garden.
Organic Mulches
Organic mulches are natural products from leaves, trees, grass, and other plant material, often from your own yard. They mimic nature, breaking down gradually over time. The advantage is that they are truly adding organic matter to the soil. The disadvantage is that they must be replenished periodically.
- Compost is readily available and breaks down rapidly to improve soil. If you don’t have your own, often towns make it available from their leaf composting facility. The disadvantage is that it must be replenished and can contain weed seeds.
- Shredded or chipped bark. Softwood bark mulch is attractive, resists compaction, and breaks down slowly. Hardwood bark is attractive but breaks down quickly and needs to be properly composted to avoid sour mulch and nuisance fungi.
- Shredded leaves and leaf mold are readily available and, if chopped, eventually break down and feed the soil with beneficial materials. The disadvantage is that leaves can mat if wet which reduces the oxygen and moisture in the soil. Avoid matted layers of wet leaves.
- Straw and salt marsh hay are inexpensive and a helpful covering; however, they decompose more quickly, may harbor rodents, and are easily blown away by the wind.
- Grass clippings are ready available but should be dried first or spread thinly to keep them from becoming a hot, slimy, stinky mess. Also, you can not use clippings from grass treated with chemicals in a food garden.
- Pine needles are attractive and stay in place better than most mulches. They are slow to break down and aren’t as acidic as you might expect, so don’t worry about them chaning the soil’s pH.
- Local byproducts, such as spent hops from a brewery, cocoa hulls, ground corncobs, coffee grounds, newspaper, or cardboard can also be much. Get creative!
Image: Mulching around salvia. Credit: Mark Herreid/Shutterstock
Inorganic Mulches
- Black plastic mulch helps warm the soil in spring, reduces water loss, and is convenient. This can make a big difference in short growing seasons. However, it’s not permeable so it’s more difficult to water; it also breaks down when exposed to sunlight and the soil under the plastic becomes very hot in the middle of summer if not shaded by leaves or covered with another mulch.
- Silver plastic mulch excels at warming soil in spring but doesn’t control weeds; the soil becomes even hotter with clear plastic in midsummer and plants can be damaged if the plastic is not shaded.
- Crushed stone, gravel, marble, or brick chips provide a permanent mulch around shrubs and trees. That said, these mulches are expensive, hard to move, and can get into the lawn. Weed seeds and soil can still find their way into the stones; an underlayer of landscape fabric will help prevent this.
- Landscape fabric smothers weeds while allowing air, fertilizer, and water to move through them and into the soil. They are treated to resist decomposition and they help retain soil moisture. It’s important to fasten the fabric down so perennial weeds do not push them up.
How to Apply Mulch
Mulching in Autumn
We do not generally use mulch in the fall, except for in bare, unplanted garden beds to prevent erosion. If you did not plant a winter cover crop (which you would till under in the spring), you should spread a thick layer of soil-conditioning compost or well-rotted organic matter over the bare soil. You could also use shredded leaves. Lay it at least four inches deep.
Otherwise, do not apply mulch to your landscape in autumn. The soil will not cool down quickly and plants may continue to grow. New growth may not harden off and can be damaged by winter cold. Also, mulching in the fall keeps the soil wet, which can lead to root rot and plant death.
Note: If you’re setting out new areas, start by clearing the surface of any debris and any rocks larger than a hen’s egg. Mow down grass or cut back weeds to the ground. Fast forward a few months and any grass and weeds below will have rotted down, while earthworms will work to gradually incorporate the organic matter into the soil below.
Mulching in Winter
Once you’ve had several freezes (often around Thanksgiving or after), then apply winter mulch around the base of any tender perennial plants or new plants. Grafted plants, like hybrid tea roses, benefit from being mulched heavily.
Shredded mulch, straw, pine needles, or shredded leaves are all good winter mulch. Apply 3 to 4 inches. It’s important to apply enough mulch in winter to keep the frozen ground completely covered so the plant remains dormant until spring no matter what type of warm or cold spells occur.
Take care NOT to put mulch next to the trunks of trees or crowns of plants, as this invites bark-gnawing rodents.
Protect branches and buds of evergreen or semi-evergreen shrubs such as rhododendrons and viburnums by wrapping them with burlap or protecting them with a tree guard filled with shredded leaves for insulation.
WARNING: Do not mulch like this! “Mulch volcanoes” will encourage rot at the base of the plant.
Mulching in Spring
Remove winter mulch in the spring when all danger of a hard frost is past so that the ground can warm and new growth won’t be inhibited.
If there are lots of weeds on the ground where you want to grow, consider a permeable landscape fabric on many of the beds.
Image: Permeable landscape fabric.
Or, lay down a layer of cardboard before adding your organic matter. Thoroughly wet the cardboard to help it break down. The cardboard will serve as a further barrier to weeds, exhausting and eventually killing most of them off. Once the growing season gets underway, you’ll find that any weeds that do manage to make it through will be much easier to remove.
After a few spring rains, when the soil has warmed, we lay down soaker hoses in each bed.
Then we cover the hoses with a fabric to speed up the change in soil temperatures and warm the soil for earlier planting.
Planting holes are cut at different spacings for different crops. Watering is efficient, and maintenance of a large area is made much easier.
Once the plants get some size on them, the fabric is covered and does not look so bad! We also use organic mulch including straw, leaf mold, grass clippings, wood chips, and shredded leaves for crops that like it cooler.
Regularly mulch with organic matter. Replace old mulch as it rots down or becomes incorporated into the soil, so that the ground is being constantly fed and gradually built up.
For more on mulching, read about mulching to control weeds and save water, and check out our guide to composting.
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Reader Comments
Leave a Comment
Organic Alternative to Mulch
Like many of your readers, I struggled using mulch in my vegetable gardens, I would rather have weeds than watch some new pest move in and devour my plants. However, without mulch, I ended up with a weedy jungle, as a working mom the time to weed never seemed to happen. Then last year I stumbled upon a new robot, Tertill, created by the inventor of Roomba. It is a solar power weeding robot that weeds your garden all season long. I now have one in each of my three raised beds and couldn't be happier. In fact, I was so passionate about the product I joined the company! So sorry if this sounds like a plug but I know there are plenty of others out there that are tired of seeing weeds and pests take over their gardens!
And its solar-powered too!
And its solar-powered too! Sounds like an interesting product!
Mulch is bad for native bees
There are many ground-nesting native bees that dig small tunnels in dirt to lay their eggs. Others may nest in holes in trees but need mud (un-mulched, plastic-free dirt) to cap their nurseries.
Yes, it is best to leave some
Yes, it is best to leave some open ground for those ground-nesting bees. I always leave space around my squash for them since they help with pollination.
Mulch Leads to Pillbugs and Ants!
I have tried mulching my garden with silver mulch, only to find hordes of pillbugs underneath it! Contrary to what many say, they do eat growing plant material, not just dead plant material. I have seen them munching potato leaves as the potatoes were growing! They also ate my marigolds!
I tried pine straw mulch, and it attracted ants! If I use hardwood, there is a slug and snail problem. I use lots of diatomaceous earth, iron phosphate, and spinosad, but it seems that the insects keep coming. The best thing for me seems to be to leave my garden unmulched and then encourage the birds, frogs, and lizards to help eat the pests. I use plenty of compost to help retain moisture. Does anyone have any other ideas?
Question more than comment
I have raised beds. I used bark mulch in them last season. I added compost to each bed last fall and turned over. The bark mulch has not broken down yet this spring. I want to remove it in the beds I'm using for root vegetables. Is there a good way to do that?
Please and Thanks!
Depending on the size of the
Depending on the size of the pieces of bark in your mulch, it can take several years for them to break down. To remove the bark chunks that are mixed in the soil you might have to screen the soil. You can make a screen by attaching wire with 1/4 - 1/2 inch square holes onto a frame made from 2X4s. Prop it up on a tarp or lay it over a wheel barrow to catch the screened soil. It is a lot of work but it will effectively remove the chunks so they won’t impede the growth of your root crops. In the future, use grass clippings or straw mulch in vegetable beds. Save for bark for permanent plantings such as perennial beds or around trees and shrubs. Keep the screen frame; it will come in handy for screening compost.
Too much mulch kills the trees!
Please tell your readers not to put too much mulch around their trees. In my residential area, the "lawn services" make money selling and piling the mulch in large thick circles around each tree. The mulch is 12 or more inches thick, and the circle is 4 feet larger than the tree trunk. You see it everywhere, in shopping centers, church yards, office parks. These "mulched" trees have fewer leaves each year, and finally die. Please put up some do & don't pictures so everyone understands they are killing their trees.
Straw is not free of weed seeds
The bales of straw I've gotten from home depot are full of seeds. It may be helpful if you're trying to grow your own hay, but I'm not. I'm worried my potatoes are going to be smothered by all the fresh green hay growing up through the straw that surrounds them.
I would be very angry with
I would be very angry with any retailer who sells weedy hay as weed-free straw! True straw is just the stalk of the grain after the tops (where the seeds are) have been harvested.
Can you take it back or have you used it all? I still would complain to them. In the future, inspect the bales as best you can and make sure no seedheads are present.
Seedy straw
When mother nature gives you wheat, make grain!
Water plants as mulch
If you have access to a pond and it has an overgrowth of pond weeds, such as chara algae, I recommend pulling that stuff out and using it for mulch. I use chara algae as mulch and it suppresses weeds, allows water to pass through, and adds zero weed seeds to your soil such as green waste can do. Once removed from their watery environment, they decompose fairly quickly so you might need to reapply one more time during the growing season, but that would seem to be a small price to pay for a natural mulch/plant food product.
That sounds like a wonderful
That sounds like a wonderful mulch and, best of all, it is free!
Mulching
Your article touts all the benefits of mulching, and the different types to use; THEN you mention how it allows various pests to show up under it. Do the benefits of mulch really outweigh the prevalence of garden pests?
I have a problem with slugs and long ago removed all mulch from my yard. I've never found a good solution for controlling those nasty creatures, and I've tried many, many treatments. I AM going to place some lime around my hostas as a preventative this year. Wish me luck!
Everything we do has its pros
Everything we do has its pros and cons. I just want you to be aware that there are two sides to the coin. For me the benefits of mulch far outweigh the cons. It is up to each individual to see what works best for them. As for your slugs, have you tried diatomaceous earth? It is sharper than lime so slugs hate it and it won’t alter your soil pH.
Mulch & snails
I have a lot of Hostas and I sprinkle dried used coffee grounds around each Hosta. Snails do not like to cross over the grounds because of their soft under bellies. It has worked for me. NO MORE HOLES! I also put Irish Spring soap around hostas to keep deer away. So far that works too.
Good luck.
Mulch
We have used newspaper as mulch. 4-5 layers of old newspaper around trees or shredded/torn around plants and then covered with wood chips works well. The newspaper allows water to pass through and disintegrates eventually. Can be used for larger areas by poking holes in the newspaper for plants. Saves a lot of work and if grass/weeds poke through, it's easier to just pull them out. Good way to recycle paper/magazines, etc.
Fall bulbs/mulching
I have planted some hyacinth and allium bulbs and added a 1-2 inches of bark-based mulch (Scotts Earthgro) over them, as recommended. Will that have to be removed in the Spring or will my plants grow up through it? I was of the understanding that one of the benefits of mulching is weed suppression and removal in the Spring, when weeds appear, seems inconsistent with it.
Mulch for Fall Bulbs
If the mulch has been laid in a thin enough layer, your bulbs should have no problem growing through in the spring. The only danger is if the mulch is too fine or too thick: Those situations would not allow air or water to reach the bulbs. So in the spring, remove enough mulch that weeds can’t grow but your bulbs will still be able to punch through. We hope this helps!
Artificial mulch
What about rubberized mulch? How thick should it be placed around plants? I'm planning on using this for borders around my newly landscaped and seeded lawn.
The idea of using chopped up
Sorry but the idea of using chopped up tires around plants makes me nervous! Bear in mind that it is flammable, toxic, and can leach chemicals and heavy metals that can contaminate ground water. If you must use it, the industry standards say to use no more than 2 inches.
Grass clippings
Why is it a bad idea to use grass clippings from a lawn treated with chemicals? My lawn is fertilized and sprayed for weeds by a local company, will that have an adverse affect on my plants?
Thank you!
The herbicides used on your
The herbicides used on your lawn can linger in the clippings for up to a year and will either kill or inhibit the growth of the plants you mulch with those clippings.
downsides of mulching
A big downside of shredded wood mulch is termites! Never put it by the house!
If termites are an issue in
If termites are an issue in your area, any mulch will provide cover for them. Best to keep all mulch away from the house and keep an eye out for the mud tubes termites build to link the ground with your wood-framed house.
shredded wood mulch / termites
I have always used shredded 100% cedar wood mulch on the gardens surrounding my house, and I don't have problems with termites. I've heard that cedar repels termites.