Mulches are inexpensive and are probably one of the best garden investments you can make. Let’s talk a little about the familiar organic mulches, since many of you probably already use them. We’ll just go over the basics. Remember to apply organic mulches 2 to 4 inches deep.
Many choices exist for those who use organic mulches. Availability, cost, and personal preference will undoubtedly influence your choice. Bark mulches, for example, can be costly unless you live near a tree service company or have a friend in the business. They do have a tendency to rob soil nitrogen from crops because of their high carbon-to-nitrogen ratio.
Remember to apply nitrogen fertilizer before you put down your bark mulch. If you have composted the bark mulch, you won’t need to use fertilizer, because the carbon-to-nitrogen ratio will change for the better during composting. Keep the bark mulch from direct contact with plants to avoid disease problems. And keep the bark mulch away from nearby wooden structures, too, because termites in the bark might munch their way on to bigger and better things.
Another organic mulch, peat moss, is expensive and, unlike bark, it’s hard to find a cheap supply under any conditions. Many organic gardeners dislike peat moss as a mulch because it requires a lot of water and time to get wet.
Another disadvantage to peat moss is that it dries out during droughts. Once it’s dry, it becomes hard and difficult to wet, and rain will run off it. It’s best to keep peat moss as an organic amendment for growing mixtures and soils where you plan to plant acid-loving shrubs.
Hulls and Shells
Another group of organic mulches that is desirable but not always available includes buckwheat hulls, cocoa shells, ground corncobs, ground tobacco stems, licorice roots, peanut shells, spent hops, and crushed sugarcane. Buckwheat hulls can cake and prevent water getting to the soil, so keep them to a 2-inch depth. Watch how you water, since forceful watering will scatter buckwheat hulls.
Cocoa shells have some fertilizer value, but keep them to 2 inches in depth. Their potash content is high, so deeper layers of cocoa shells might harm sensitive plants. Ground corncobs, unless you object to their light color, are relatively problem free. Don’t use ground tobacco stems to mulch tomatoes, peppers, eggplants, dahlias, or any other plants susceptible to tobacco mosaic virus.
Tobacco stem mulches may carry this virus. Licorice roots resist blowing and floating, making them ideal candidates for sloping gardens. Several qualities of peanut shells, such as their significant nitrogen content, ease of application, durability, and attractive appearance, make the shells an excellent mulch.
Spent hops have some nutrient value and resist blowing. If you use spent hops, make sure they are aged; if they are not, they may heat up, have an unpleasant odor, and even damage your plants. Some mulches, in particular sawdust and wood chips, are relatively common and inexpensive, but have some decided drawbacks.
Unless you have composted them (and few people do), these woody materials have a very high carbon-to-nitrogen ratio. The high ratio means that these woody materials will steal soil nitrogen away from your plants as they decompose. Therefore, you have to put down some nitrogen fertilizer before you put on the mulch, if you want to avoid depleting your soil. This need for fertilizer translates into extra cost and work. Sawdust and wood chips are more trouble than they’re worth.
Compost and Straw Mulches
Now on to the last category of organic mulches: compost, grass clippings, leaves, straw or hay, and salt-marsh hay. Compost makes an excellent mulch, especially if your soil is low in organic matter. It’s one of the few mulches that also acts as a slow-release fertilizer.
Water from your hose or from rain leaches out nutrients that microbial activity has converted to soluble forms. By the end of the growing season, the lower part of the compost mulch has become part of the upper soil profile. In a few years, you can have an organic-rich soil without any work.
The plus is that you need far less compost to take care of the area around or under plants than you need for a mulch covering a much larger area. Still, if you make lots of compost, you might consider using the excess as a mulch. If you don’t recycle your grass clippings to your lawn with a mulching mower, you can use the clippings as a garden mulch. Just don’t apply your layer of grass clippings all at once.
Do it gradually, because a thick layer of green clippings will heat up and form a dense mat as decay sets in. The mat will restrict the flow of air and water to the soil. Apply the clippings in thin layers and allow each layer to dry and turn brown before you add the next layer. One bonus to using grass clippings is that they contain nitrogen, which will eventually leach into your soil, thus slowly fertilizing your plants.
You can also use leaves as a mulch, as long as you’re aware of a couple of problems that exist. First, leaves are available mostly in the fall. Such timing is great for winter mulches or the leaf compost pile but is bad for a summer mulch. To get around this problem, you can pile the leaves until next year.
The other problem is that leaves can mat into a soggy mess. To overcome the matting problem, you can mix the leaves with fluffy materials, such as hay or straw, or you can shred the leaves. Leaves do release some nutrients during decomposition as a mulch; but many people still prefer using them to make leaf compost.
Straw, hay, and salt-marsh hay all make reasonable mulches. Straw is useful mulch for growing strawberries. You can sometimes buy spoiled hay at a modest price. The going rate for unspoiled hay or salt-marsh hay argues against their use as mulches; however, if you find a bargain, these mulches are great for vegetables.