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Organic Mulch: What It Is And How to Choose The Best One
Imagine if you could magically minimize the need to weed, water, and fertilize your garden.
Well, your gardening fairy-godmother, organic mulch, is ready to grant your wish!
Organic mulches create a cozy blanket over your soil, which protects your soil from drying winds, blistering sun, and the 40,000 dandelion seeds your neighbor blows into your yard with their lawnmower every weekend.
And there are lots of great natural mulches to choose from. But picking the right one can feel overwhelming.
You’re at the store eyeing all the organic mulch choices: wood chips, colored wood, straw, shredded bark, pine straw, and seed hulls. Then you see compost and wonder “can that be used as a mulch, and what about shredded leaves or lawn clippings?”
So, with all those choices, how can you know what’s the best organic mulch for your garden?
- If you already know you want to use an organic mulch, download my mulching cheat sheet and then skip down to the types of organic mulch I recommend.
- If you’re not sure that organic mulch the best choice, learn about the benefits of organic mulch and then use my three-step method for choosing the perfect mulch for your yard.
Organic mulch can do many good things for your soil and plants. Organic mulch can
Organic mulch keeps the soil underneath it shaded. This prevents most weed seeds from germinating because they typically need light to germinate. And since mulch keeps the soil loose and moist, pulling the few weeds that pop up is a lot easier.
Add organic matter to your soil
As organic mulches decay, they add organic matter to your soil. When your soil’s micro- and macro-organisms come up to the surface for a snack, they pull that organic matter back down with them when they travel back into your soil.
Reverse or prevent soil compaction
A thick layer of mulch helps disburse your weight as you walk through your gardens, which helps to prevent compaction. As large soil organisms like earthworms and pill bugs pull the decaying mulch into your soil, they help glue your soil particles together, which creates air pockets that help to reverse soil compaction.
Give your garden a finished look
Mulch will give your garden a finished look by filling in the empty spaces around plants.
Reduce your water bill
Water evaporates slower when an organic mulch covers your soil. That means you’ll water less, and your plants will have a steadier stream of water available to them.
Keep your plants clean
Natural mulches help to reduce soil splash-back on plants, which cuts down on soil-borne plant diseases.
Protect your soil from temperature swings
Organic mulch acts as an insulator. In the winter it can keep plants from heaving out of the ground, and it’ll keep your soil cooler during the heat of summer. If you live in a cold climate, organic mulch might not be the best choice for your heat-loving vegetables, since the mulch will prevent your soil from warming up. A plastic mulch would be a better choice.
Stop your topsoil from eroding
Because organic mulches break the fall of water when it rains, they stop topsoil from washing away.
Protect trees from lawnmowers and weed eaters
Spreading organic mulch around trees planted in lawns creates a barrier between the tree and your lawnmower or trimmer.
Before we get into the details of each type of organic mulch, download my free, printable mulching cheat sheet. It walks you through my easy three-step process for choosing the best mulch for your garden.
Wood Chip Mulch – Highly recommended for all ornamental gardens
Wood chips can come in many sizes. Some smaller sized wood chip mulches would better be described as “ground” wood mulch.
The smaller the chip size, the more likely it is to stay in place. The larger chips are lighter, blow around more, and can float away in strong rain storms.
Wood chip mulch is best for mulching trees and shrubs, flower beds, perennial flowers, orchards, and walkways in flower and vegetable gardens.
Depth: 2-4 inches, depends on the size of chips, or how finely ground it is. Bigger chips can be applied more deeply.
Advantages: Is usually attractive. Adds organic matter – this is especially helpful for perennial plantings where you can’t easily amend the soil.
It also lets in water, prevents evaporation of water, suppresses weeds well, moderates soil temperature, and is free of weed seeds. Smaller chips or more finely ground wood is less likely to blow or wash away than larger chips. It doesn’t readily compact. And finally, it reduces, and often, reverses soil compaction.
Disadvantages: Larger chips can blow or float away. It must be topped off — top-dress larger chips every 1-3 years, smaller chips every 1-2 years.
- I recommend uncolored wood mulch. Read my review of colored wood mulch.
- Don’t create mulch volcanoes when you mulch trees.
- Don’t install wood chip mulches over landscape fabric.
- Wood chip mulch isn’t recommended in vegetable beds next to plants but is fine to use in vegetable garden pathways.
Will wood chips tie up nitrogen in my soil and steal it from my plants?: Good news! This is a myth.
- If the mulch sits on top of your soil, any nitrogen tie-up will be tiny, and won’t affect your plants.
- But, if you turn it under, or till wood chips into your soil, it’ll tie probably tie up some nitrogen. So, if you don’t turn it under, wood chip mulch WON’T rob your plants of nitrogen.
- In annual flower beds, rake off the mulch before planting, and re-mulch after your plants are in, to avoid turning it under and creating that possible nitrogen deficit.
Straw Mulch – Highly recommended for vegetable gardens
Straw mulch is the best mulch for vegetable gardens. It’s especially helpful for keeping your soil cool in the warmer months. If you want to warm your vegetable garden soil, see plastic mulches for vegetable gardens.
Depth: 2-3 inches.
Advantages: It lets in water, prevents evaporation of water, adds organic matter, suppresses weeds well, moderates soil temperature, and can be turned under at the end of the season.
Disadvantages: It can blow around easily. It may have weed seeds in it. It has to be replenished annually. And it’s flammable. Some say it’s not super attractive.
- Purchase straw, not hay. Hay has lots of weed seeds in it! See this article about possible dangerous pesticides in straw.
- Pre-sprout weed seeds in your straw by watering the bales a couple of weeks before spreading the straw. Remove any that have sprouted as you spread it.
- Get tips on how to mulch your vegetable garden.
Corn Stalks and Corn Cobs – Recommended
This mulch is best for vegetable gardens.
Depth: 2 inches.
Advantages: Corn stalks make a good winter mulch. It lets in water, prevents the evaporation of water, adds organic matter, suppresses weeds, and moderates soil temperatures. It’s free of weed seeds and can be turned under in the spring.
Disadvantages: It can mat or blow away. Shredded stalks aren’t the most attractive mulch. It may not be readily available where you live.
- Stalks should be shredded, and cobs should be ground up.
- Mix the stalks with straw to prevent matting.
- If you want to use stalks from your own garden in the spring, you’ll need space to store it over the winter.
Cotton Burrs – Recommended
Cotton burrs are best for vegetable gardens and are recommended if you can find a source of burrs from a producer who doesn’t use a lot of pesticides and doesn’t chemically defoliate the plants.
Advantages: They let in water, add organic matter, prevent water from evaporating, suppress weeds, moderate soil temperatures, and are weed-seed-free.
Disadvantages: Cotton may have had a lot of pesticides applied to it.
Notes: Don’t use burrs from chemically defoliated plants.
Evergreen Boughs – Recommended
Evergreen branches are best to use on perennials or small shrubs that need protection over the winter.
Depth: Several layers.
Advantages: Good for insulation during the winter to prevent heaving and frost damage.
Notes: Remove them in the spring when the soil warms up, and the threat of frost has passed.
Green Manure/Cover Crops – Recommended
Cover crops improve your garden soil and reduce weeds. Examples include ryegrass, winter rye, oats, buckwheat, barley, and annual clovers.
Cover crops are best for vegetable gardens and orchards.
Advantages: They let in water, add lots of organic matter, prevent water from evaporating, suppress weeds, and they moderate soil temperatures while they’re growing. As a bonus, they attract many beneficial insects when they flower.
Disadvantages: You won’t be able to grow vegetables while you’re growing a cover crop.
Notes: You must turn them under or cut them down before they go to seed. Otherwise, they’ll spread and become a nuisance.
Lawn Clippings as Mulch – Recommended
Lawn clippings are best used on your lawn if you have a mulching mower. Mulching your lawn clippings can reduce your lawn fertilizer needs by up to 25%. The next best place to use them is your compost pile. You can use them in your vegetable garden if you’re careful about how you apply them.
Depth: up to one inch.
Advantages: They let in water, prevent evaporation of water, add organic matter, they’re typically free of weed seeds, and they can be turned under at the end of the season, and they’re free.
Disadvantages: It can mat or blow away. When it mats, it creates a stinky, slimy mess. Allow the clippings to dry out first, and apply them in thin layers. Add additional thin layers as they decompose.
Notes: Don’t use clippings in your garden if they were sprayed with weed killer, or if the lawn has gone to seed or has many weeds.
Leaf Mulch – Recommended
Leaf mulch (shredded leaves) can be used in either your vegetable garden or ornamental garden.
Depth: 2 inches.
Advantages: It lets in water, prevents evaporation of water, adds organic matter, it’s typically free of weed seeds, it can be turned under at the end of the season, and leaves are free.
Disadvantages: Can easily mat or blow away. You must collect them in the fall and have a place to store them over the winter if you want to use them in the spring. They can look messy.
Notes: Mix shredded leaves with straw to prevent matting.
Living Mulch – Recommended
Leaf mulch (perennial groundcovers) are best to use in ornamental gardens or orchards.
Advantages: They’re attractive. They let in water, prevent the evaporation of water, add organic matter, suppress weeds somewhat, moderate soil temperatures, and they won’t blow or wash away.
Disadvantages: Can take over parts of your garden if you choose an aggressive ground cover. Some require maintenance like annual mowing or pruning.
Notes: Examples include thyme or Veronica for ornamental gardens and clover for orchards.
Nutshells, Cracked or Ground – Recommended
Nutshells are best for ornamental gardens.
Depth: 2-3 inches
Advantages: It lets in water, prevents evaporation of water, suppresses weeds, is free of weed seeds, and moderates soil temperature. Some are attractive, and some are slow to decompose.
Disadvantages: These mulches may be expensive unless you have a nut processing plant nearby. Some shells can have sharp edges. It can blow around easily. It’s not suitable for slopes. And some can look messy.
Notes: Examples include: Pecans, Peanuts, and Hazelnuts. Avoid using walnut shells around plants sensitive to juglone.
Pine Straw – Recommended
Pine straw (aka pine needles) are best for ornamental plantings and orchards. They can also be used in your vegetable garden.
Depth: 1.5 – 3 inches.
Advantages: It lets in water, prevents evaporation of water, moderates soil temperature, suppresses weeds somewhat, and lasts a long time. It’s free of weed seeds and provides good winter protection for fall-transplants because it resists compaction. Disadvantages: It can’t be turned under at the end of the season. It’s a fire hazard. It can look messy. It adds little organic matter. And it doesn’t suppress weed as well as other mulches like wood chips or straw.
- Pine needles don’t affect soil pH, contrary to popular myth.
- You may only need to top off this mulch every few years.
- If you have large long-needled evergreens, you can harvest your own mulch.
Seed Hull Mulches – Recommended
Seed hull mulches (from cotton, buckwheat, cocoa beans, and rice) are best for vegetable gardens.
Depth: 1-2 inches, 1-inch max. for cocoa hulls
Advantages: Some hull mulches are attractive. They all let in water, prevent evaporation of water, add organic matter, suppresses weeds, moderates soil temperature, free of weed seeds, can be turned under at the end of the season. Some are more attractive than others.
Disadvantages: They can blow around because they’re lightweight. Cotton may have had a lot of pesticides applied to it. Cocoa mulch may get moldy if it’s used in humid or damp conditions. It can also form a mat and can have high levels of potassium in it.
Notes: All hull mulches must be replenished annually.
Newspaper and Cardboard – Recommended
Newspaper and cardboard can be used anywhere you want to suppress weeds.
- Newspaper, a few sheets thick
- Cardboard: 1 layer thick
- Always wet the newspaper as you lay it down, and overlap the edges.
- Soak the cardboard before laying it down to be sure that both sides are wet.
- Cover the newspaper or cardboard with 2-3″ thick layer of either straw or woodchips.
- Keep the mulch and soil moist. Check to make sure that the newspaper and cardboard aren’t drying out.
Types of Organic Mulch That I Recommend With Reservations
Coffee Grounds – Recommended with reservations
Coffee grounds are best used in ornamental and vegetable gardens. But they aren’t good to use as a mulch by themselves.
Depth: ½ inch
Advantages: Coffee grounds let in water, moderate soil temperature, and add organic matter. It can be turned under at the end of the season if you cover it with a second mulch that also can be turned under.
Disadvantages: Coffee grounds compact and crust over unless they’re covered with another mulch. And layers thicker than ½ inch compact and crust over more.
- To use coffee grounds as a mulch, apply a half-inch layer. Cover that with a 3-4″ layer of coarse organic mulch (wood chips or straw).
- Don’t use coffee grounds near seeds; they’ll reduce germination rates.
- Don’t till un-composted coffee grounds into the soil.
- The best use for coffee grounds in your garden is to compost them.
Colored wood mulches are best used in ornamental gardens.
Depth: 2-4 inches, depending on the size of the chips.
Advantages: It moderates soil temperature, prevents the evaporation of water, is free of weed seeds, and adds organic matter. Some people find it attractive when it’s new.
Disadvantages: It fades to grey unevenly which can make topping it off more work than it should be. You may also find you have to top it off more often than natural wood mulch.
Compost – Recommended with reservations
Compost can be used in most gardens. Rock gardens and native gardens that need lean soil are the exceptions.
Depth: 1-2 inches, depending on how much organic matter you need to add to your soil. See the notes below.
Advantages: It lets in water, and adds organic matter. It can be turned under at the end of the season. Lets in water and adds organic matter. Commercially produced compost is free of weed seeds.
Disadvantages: Weed seeds will go crazy germinating in your garden if you don’t cover the compost with another mulch that suppresses weeds.
- Get a professional soil test to see if you should add compost to your soil.
- 5-6% organic matter is the recommended amount.
- It’s best to cover the compost with a layer of another mulch like wood chips, straw, or leaves to suppress weeds.
Shredded Wood (gorilla hair mulch) – Recommended with reservations
Depth: 2-3 inches
Advantages: It moderates soil temperature, adds organic matter, prevents evaporation of water, and controls weeds. It’s free of weed seeds and is long lasting.
Disadvantages: It compacts and forms a barrier against water.
Notes: Only use this type of mulch if you have drip irrigation set up under the mulch, or you live in a wet climate where rain will penetrate the mulch.
Types of Organic Mulch That I Don’t Recommend
Bark Chips or Shredded Bark
Bark mulches are expensive, tend to compact and form a barrier against water, and aren’t as good at conserving water as wood-chip mulch. Wood chip mulch is the better choice.
Peat moss is a good soil amendment in certain situations but is a terrible choice for mulching. It blows away easily. It crusts over. It becomes hydrophobic when it dries out. And it’s not environmentally sustainable.
Salt Marsh Hay
Salt marsh hay is a mulch available in the northeastern U.S. Salt marsh hay is harvested from ecologically sensitive coastal estuaries and flood plain areas. The continued seasonal harvesting of salt hay disrupts and damages these areas.
Sawdust and Wood Shavings
Put sawdust and wood shavings in your compost pile rather than use it as a mulch. It compacts, crusts over, and resists water. It shouldn’t be turned under as it’ll tie up nitrogen in the soil while it decomposes.
If you use it, before applying, mix one pound of nitrogen per 5 bushels of sawdust to prevent nitrogen tie-up in the soil.
Download Your Free Cheat Sheet and Choose the Best Organic Garden Mulch
This cheat sheet will help you choose the perfect organic mulch for your garden in three easy steps.
- Focus on what plants you want to mulch.
- Choose the top three things you want this mulch to do for your garden.
- Once you have the answers to those questions, look through the list of mulches to find the perfect mulch for your needs. The chart includes details about 26 mulches. I grouped them by mulches I:
- recommend with reservations, and
- don’t recommend
Here’s a sneak peek of your printable cheat sheet:
Are there any organic mulches that I missed? If so, let me know in the comments and I’ll add them to the list.
Now It’s Your Turn: What organic mulch did you choose off the list? Share in a comment below!