Mulch is among a gardener’s most useful allies. In fact, spreading it over beds or around plants can prevent weed growth, deter pests, and improve soil moisture retention. Mulch also keeps the soil cool, protecting plant roots from extreme temperatures. A layer of organic mulch can also improve the appearance of your flower or vegetable beds, and will slowly break down over time, improving the soil’s fertility and encouraging beneficial soil organisms.
If you want to learn more about mulch—including how to use it—then this guide is for you.
Biodegradable Mulch
In simplest terms, mulch is biodegradable material that can be placed on the surface of cultivated soil.
Over time, biodegradable mulches break down, enriching the soil. They also help to discourage weeds, conserve moisture and improve the aesthetic appeal of your flower or vegetable beds.
Some of the most commonly used biodegradable mulches are:
1. Leaves
Leaves are one of the best forms of mulch: not only do they deter weeds, they also attract beneficial garden dwellers, such as earthworms. You can use leaf mulches anywhere—including on vegetable beds—but they look particularly good in woodland or natural gardens.
Spreading leaf mulch onto beds in early spring will allow your plants to grow over the top, blending the mulch into the garden. Alternatively, apply leaves to vegetable beds in the fall. The leaves will decompose during the winter months, enriching your soil and deterring weeds, readying the bed for spring planting.
If you have trees on (or overhanging) your property, use a lawn mower with a bagger to shred fallen leaves. This cuts them into the ideal size for mulching.
Be warned that if you choose to spread un-shredded leaves in wet weather, they can mat together and repel water. This issue is solved by raking the leaves, gently separating them and tearing them apart.
2. Wood Chips
This is of the most common and easy-to-use mulches. Wood chips can be spread on flower and shrub borders as well as vegetable beds, and can be used to create a natural looking garden path.
Decorative wood chips and shredded bark are readily available in garden centers and DIY stores. If you require a large amount, try your community yard waste collection site or any local tree-care companies.
Community yard waste collection schemes are particularly great because they often offer chipped garden debris for free, or at a reduced rate. Don’t forget to contribute your own waste in return! Chipping your Christmas tree is more beneficial than leaving it on the curb for collection.
3. Bark
Like wood chips, bark can be used anywhere in your garden. However, it’s best used around trees, shrubs, and on beds that you won’t be digging or planting in a lot. This is because woody mulches are slow to decompose into the soil. As a result, you’ll have to move them every time you want to plant something in the bed.
4. Grass Clippings
Nitrogen-rich grass clippings are ideal for mulching vegetable beds. In addition, you can leave some on your lawn after you finish mowing to enrich the grass. They’re also one of the best mulches for suppressing weeds.
Grass clippings don’t come without their issues, however. Since they’re high in water content—like other green plant matter—they’ll decompose rapidly, becoming slimy in the process. They can also release an unpleasant odor. Also, just like leaves, grass clippings may mat together in rainy weather, preventing water from accessing your beds. Raking the clippings gently will separate them and counteract this issue.
Don’t use grass clippings as mulch if you’ve used weed killer or chemicals on the grass, as synthetic lawn care products can harm flowers and vegetable plants. For the same reason, don’t place chemically treated grass clippings in your compost pile.
5. Compost
As long as it’s completely broken down and weed free, compost mulch can be used anywhere. Just keep in mind that compost can be a dry mulch. As a result, plant roots can struggle to establish themselves if conditions are too dry.
If you’re applying compost, spread it thinly and place another wetter mulch, such as leaves, on top. This keeps the compost damp and biologically active, enriching the soil and benefiting your plants.
Alternatively, you can use the compost to side-dress your plants during the growing season. This insulates the roots, slowly releasing nutrients into the soil.
6. Straw and Hay
Since these are so slow to decompose, one application of this mulch lasts throughout the growing season. It’s also a great home for spiders and other beneficial insects, so unwanted pests are kept to a minimum. When the growing season is over, simply rake up the straw and hay and dig it into the soil.
Straw or hay can also be used to line paths, making them less muddy. Just make sure that you use weed- and seed-free hay, or you’ll sow those species into your garden.
7. Newspaper
In today’s environmentally conscious world, many newspapers now use organic dyes, particularly black and white print. As a result, shredded paper is an increasingly popular mulch option. The organic printing inks won’t harm your garden, so newspaper is safe to apply as a mulch.
Layering 4-8 sheets of moist newspaper (damp newspapers stick together and stay in place) around your plants acts like any other organic mulch, suppressing weeds and helping moisture retention. You can then add another organic mulch on top, creating a 3-inch-thick layer at most. This double approach will last throughout the growing season, and you can use shredded newspaper in the same way.
Newspaper can also be used to jump-start a vegetable bed. Simply lay a couple of sheets of newspaper over the grass to smother it before adding the soil and seedlings.
Non-Biodegradable Mulches
Both biodegradable and synthetic mulches discourage weeds, but only organic mulches break down and enrich the soil. As such, organic mulches may seem the obvious choice for vegetable gardeners. However, a black, plastic mulch around your heat-loving tomatoes not only keeps the soil warm during the day, but also keeps the soil warm at night, protecting plants from temperature drops.
Non-biodegradable (or synthetic) mulches also last for longer than biodegradable or organic options.
8. Synthetic Mulches
These will suppress weeds and improve soil heat and moisture retention, but won’t break down or improve your soil. This also means that unlike organic options, synthetic mulches don’t need to be regularly replaced.
Because of this, synthetic or plastic mulches are a good choice for foundation planting. You can also apply them around trees and shrubs that require little fertilization or regular attention. Synthetic mulch isn’t the most attractive option, but it’s a functional one. Add another mulch such as bark or stones on top to improve your space’s aesthetic.
Plastic mulch will keep the soil warm, greatly benefiting vegetable beds, especially vining crops such as melons or strawberries. However, in the hottest months, this mulch may heat the soil too much, smothering your plants. Cutting small holes into the plastic or laying a permeable option, such as landscape fabric, will allow moisture through, cooling the soil. Additionally, laying an organic mulch on top will also help to cool things down.
9. Landscape Fabrics
Also known as geotextiles, these are more permeable than plastic mulch. As such, they let air and water through while suppressing weed growth. Just note that prolonged exposure to light causes them to degrade. Covering with an organic mulch will extend the lifespan of the fabric, and improve its overall aesthetic appeal.
10. Gravel or Stone
Gravel or stone mulch is great for an area that requires good drainage. These are also a great way to keep the soil warm. Stone mulches work particularly well in Mediterranean herb gardens, as well as other beds that appreciate a little extra heat.
Although these are very aesthetically pleasing, remember that this is also one of the hardest mulches to remove. Be sure to give it a lot of thought before adding it to a bed.
How to use Mulch
Only mulch areas that have already been weeded. If you’re using an organic mulch lay down enough to discourage any weeds that are left from emerging. In shady areas a 3 inch layer will be fine, but in warmer beds you may need to double the thickness. If you have a particularly weed ridden bed you may need to double-mulch. Newspaper followed by either bark, grass cuttings or leaves is an effective combination.
When to Apply
The best time to mulch is between mid and late spring. You can also apply mulches in the fall when the soil is moist and warm. Just don’t apply it in the winter. Mulching cold soil can slow the soil from warming up, so your plants will be slower to grow.
After the last frost date has passed, remove any mulch that you applied the previous fall from around your perennials and bulbs. This will warm the soil and encourage growth. Don’t mulch in the late spring or summer either, as the soil can be dry during hot periods. Adding mulch at this point can prevent water from reaching the beds, leaving plants even thirstier.
How to Apply
There’s no real skill to applying mulch: simply put it on your bed. You can mulch new and established beds and borders almost completely—just take care not to smother low-growing plants.
Don’t lay the mulch right up to the plants, as wet mulch piled against stems can cause them to rot. It can also encourage rodents to visit your shrubs. Keep mulch about one inch away from stems and crowns.
Once the mulch has rotted, either work it into the soil or remove it. If left in place, mulch can harden, making it difficult for water to penetrate the soil.
Potential Mulching Problems
As long as you apply it properly, taking care not to smother plants or pile the matter up around stems and crowns, mulch is largely problem free.
After adding it, remember to give your plants extra water. If you’re fertilizing your plants, simply fertilize over the mulch. White fungal mycelium often grows in organically mulched soil, but this is perfectly normal and harmless.
Happy mulching!
