Mulching is the art of nourishing and protecting your soil with a layer of organic matter applied evenly to the surface. It mimics the way that nature recycles organic matter to build soil.
Nature abhors bare soil and goes to great lengths to cover it. Wherever you find undisturbed communities of plants, you’ll find the soil surface covered with leaf litter, plant debris, and other organic matter protecting the delicate microorganisms underneath.
Next time you’re in the West Desert of Utah, get down on your hands and knees and take a look. You’ll find that even there, the soil is covered, protected from that harsh desert sun.
Underneath the layer of mulch, where it meets the soil, is known as the duff layer. This is where the highest rate of microbial activity occurs. By maintaining a mulch layer on top of your garden soil, you are actively harnessing the power of countless bacteria, beneficial fungi and other organisms, to recycle organic matter into plant available nutrients. This is the art of building soil; boss move, my friend, that’s how nature do.
Mulching helps prevent weeds, as it robs seedlings of the light they need to grow. Those that do manage to germinate are far easier to remove, as they they struggle through the mulch layer, searching for the light.
Mulching also has a dramatic effect on retaining moisture in the soil. By reducing the temperature of the soil, evaporation is slowed. Keeping the soil moisture consistent improves the health of the plants, as most of our vegetable crops enjoy even and consistent moisture.
When is the best time to mulch? While it may seem logical to answer “always,” this isn’t quite the case. Mulch has a great insulating quality, which keeps the soil cooler than it would be when exposed. Because of this, it is beneficial to remove your mulch layer in early spring to allow the sun to warm the soil for planting early crops. Once cool weather crops are growing vigorously, the mulch can then be replaced. For heat-loving crops such as tomatoes and peppers, I’ll keep my mulch layer removed until early june, to maximize the soil-warming effect of the sun.
Mulch should also be removed when starting plants from seed, as the very qualities that help to deter weed growth will prevent the proper germination of your desired seedlings.
Applying mulch is as simple as spreading an even layer of the organic matter of your choice on top of your garden beds. When applying it, don’t mulch right up to the base of plants. The crown of a plant, or where the stem meets the roots, generally benefits from being dry, and mulching the base of plants can encourage rot, especially in young plants.
Types of mulch
Composted tree material / green waste
Pros: inexpensive in bulk, looks great, easy to apply, long lasting nutrition
Cons: can be expensive in bags, single use plastic packaging
The key word here is composted. It is important to never use uncomposted wood shavings or chips in your garden, as this will tie up available nitrogen for quite some time as the soil works to break down the material. This is my mulching material of choice, as it is wicked easy to apply, looks really clean, and for those of us with large gardens it is readily available in bulk from local suppliers such as DT Green Waste or Transjordan Landfill. Both of these companies recycle and compost local green waste, with no composted biosolids. For those with smaller gardens, bagged products are readily available at all garden centers; be prepared to pay substantially more for that convenience.
Pros: super cheap, easy to apply
Cons: little to no nutrition, messy to transport, messy in the garden
It’s hard to beat a bale of straw for covering a large area for a little bit of money. However, it tends to blow around, and since it is the leftover stalks of plants harvested for grains, there is little in the way of nutrition for the soil once it breaks down. If you’re ambitious and looking to haul a bail or two inside your vehicle, make sure to put down a tarp, or be prepared for “forever straw” in your carpet.
Pros: super cheap, easy to apply, sustained nutrition
Cons: possible weed seeds, messy to transport, messy in the garden
Like straw, a bale of alfalfa hay goes a long way and makes quick work of a mulching job. However, since hay is harvested from the living plant and quickly dried, it provides a long-lasting source of nutrition as the microbes break it down. Like straw, it can also be messy during transport and after installation. Certified organic hay is recommended.
Pros: free, readily available
Cons: hard to keep in place
Dried leaves that have been shredded or chopped with a leaf vacuum make a good mulch. Be careful with full-sized leaves, as they can often form a “mat,” which will rob your soil and plant roots of valuable oxygen.
Piling all of your leaves in a deep mulch on your garden beds in the fall is a fantastic way to take advantage of the insulating power of a deep mulch, which sustains the soil warmth gained over the summer months for increased microbial activity into early winter. Worms, detritivore insects and beneficial fungi absolutely love this layer, and is a great way to build soil fertility and organic matter in the off season. (Remember to remove it early next spring to prevent smothering if you have perennials or self-seeding annuals.)
Pros: free, loaded with nutrients
Cons: the fact that you still have a lawn, potential herbicide residues
Grass clipping are another free option, although warrant a number of cautions. Fresh clippings can form a “mat,” similar to whole leaves, which will rob your soil and roots of oxygen, so be careful not to apply too deeply at once.
Grass lawns are also one of the highest uses of herbicides, fungicides, and insecticides in the US, far exceeding chemical inputs in agriculture per acre. If you use grass clippings, make sure they’re coming from an organically managed lawn.
A word about synthetic mulches
These should never be used in the garden. Made from materials such as shredded tires, these mulches are mulch in name only. They provide little benefit, release toxic compounds during their slow degradation, and have no place in a vegetable garden.
James Loomis is a full-time urban farmer, educator and permaculture hooligan.