‘Mulch’ is a protective layer of material that is spread 3-6 inches deep on top of exposed soil between plants. Mulch is by far the best way to preserve the water in your soil and can be a very effective way of feeding your soil and regulating growing temperatures. Mulch can be almost anything: straw, grass clippings, corn cobs, river stones, pea gravel, chipped bricks, bark chips, leaves, peat moss, seaweed, wood ashes, sawdust and so on.
Nature abhors uncovered and exposed ground. Walk out into nature and look down. In a healthy ecosystem you will find very little, if any, bare ground. Nature will always try to cover soil with either plant growth, decaying matter or even inorganic matter. Trees drop their leaves and cover the floor of a forest for example. You’ll want to imitate the same process in your garden.
As mentioned above, mulch helps preserve water and regulate the temperature in your soil but it also prevents the growth of weeds, protects soil from compaction, cuts down on erosion and, if organic, feeds your soil. As the mulch decomposes, it provides that vital organic matter to your soil, encourage microbe growth and shelter earthworms. All that organic matter keeps your soil loose so that it can retain moisture and promote root growth.
Types of Mulch
Before heading to the store to buy mulch, look around your yard and house.
Grass clippings make excellent mulch. They are easy to spread between small vegetable plants and if you have a lawn, you will have a steady supply to layer on throughout the summer.
Old newspaper also works quite well, especially against weeds.
Leaves are another material to use as mulch. Remember that forest floor? Leaf mold from the decomposed remains of leaves gives the forest floor that spongy structure and holds a heck of a lot of water.
You can also use old cotton or wool clothing cut into strips. You can even use old carpet like this, too.
Bark chips can be purchased at most garden centers. They can be a bit pricey and do not decompose very rapidly but they will preserve soil moisture and eventually help your soil – and they look awfully nice in the garden.
Hay or straw can also be purchased as can seaweed mulches.
Another type of mulch is so-called ‘living mulch’. These are plants that grow very close to the ground under the main crop. They can grow very fast and have all the benefits of other types of mulch. Keep an eye on these that they don’t eventually compete with your main crop.
Some recommend plastic mulches but I strongly urge you to avoid this ‘plasticulture’. For one, you are adding nothing to your soil except, possibly, leached chemicals. Worse, covering your soil with plastic can kill the microbes and other life that will make your garden vibrant. Under plastic the soil can’t get the water, air and nutrients it needs to thrive. Plants grown with plastic mulches can very weak root systems that leave the plant malnourished and subject to damage from winds.
Here’s a great resource to the advantages and disadvantages of different types of mulch, including details on calculating how much mulch to use and spreading mulch.
You will use different types of mulch for different situations. For example, in my garden I use gravel as mulch around perennial plants. The gravel protects my soil from the sun’s rays and the drying effects of the wind. The soil under the gravel is moist and maintains a constant temperature. The gravel also helps extend my growing season by absorbing the heat from the sun and then radiating it back at night. I have found that I can add a week to ten days on my growing season with gravel mulch.
Be thoughtful about the use of inorganic materials as mulch. They can be difficult to remove and will not feed your soil. To deal with this, every fall I scatter quality ready compost on top of the gravel by hand and then let the winter snows and spring rains wash it in.
Gravel however, will not be the mulch of choice for your annual vegetable garden (although many Native American tribes did use river stones as mulch in their incredibly productive vegetable gardens). Once I put my spring transplants in the garden, I scatter some fresh kitchen scraps or grass clippings between each row of vegetables and then cover that ‘soil food’ with a generous layer of straw. I make sure to find straw that has no seeds in it so I don’t have to deal with more weeds the next year. I have seen small lizards come to live and/or hunt in my mulch. I’ve seen these little helpers picking pests such as squash bugs from my vegetables, so I look at mulch as pest control also!
The area you mulch should include as much of the root zone as possible. For my trees and larger shrubs (such as my golden currents and gooseberries) I mulch an area that extends about 4 feet out from the base of the tree and to the drip-line of the shrub. I also pull the mulch about 2 inches out from the base of the trees to avoid bark decay. The mulch should not be touching the tree. Here is a good rundown of how to mulch trees and shrubs.
I mulch very deeply…4-6 inches…as I live in a high altitude desert environment. While a thick layer of mulch is a good thing be careful that it is not too thick (not more than 6 inches) as the roots of your plants may seek out moisture in the mulch and not deep in the soil.
When you apply your mulch will depend on what you are trying to achieve. I mulch my trees in the autumn to protect them from the cold. Again, I first dump a bucket of kitchen scraps around the drip line of the tree and then put down a 5-10 inch layer of straw and grass. Mulch can keep the soil from freezing too deeply.
In the vegetable garden I wait to apply the new layer of mulch until after the plants are up or after I have put in the transplants. For the perennials, I wait until late in the spring or even into early summer to put down a layer of mulch. Some people like to mulch early in the spring to encourage the warming of the soil. This can work in dry environments but in wetter regions this may keep your soil too wet or waterlogged which will in turn rot your seeds. Your own observation will be key on figuring this one out.
And, check out sheet mulching. It’s an effective way to mulch that promotes the natural composition of a forest floor. Sheet mulching works great in vegetable gardens and around trees or shrubs.
Now, go forth and mulch!!
Jim O’Donnell gardens in the mountains of northern New Mexico. A certified permaculture designer and ecological restoration specialist, Jim’s first book Notes for the Aurora Society was published in 2009.