mulching
Mountains of mulch disappear from garden centers every spring to be trucked around the city and spread over the Lexington landscape. This can be a good thing. Mulch inhibits weed germination and growth. It holds soil moisture, preventing your plants from drying out too quickly. It helps keep plant roots cooler during the hot summer. And, depending on what type of product you use, mulch can add some welcome nutrition to your garden soil as it breaks down.
However, there are some misguided notions about mulching out there.
Dr. Bill Fountain is an extension professor of arboriculture and landscape management at the University of Kentucky. The two of us were working on a mulch display for the recent Arbor Day event at the Arboretum and we got to talking about some of these erroneous ideas. Out of our conversation came Fountain’s publication, entitled “Mulch Myths.” Here are the myths we came up with, along with explanatory comments.
Myth: Mulch will attract termites to my house.
This is an understandable but mistaken belief. Termites are not attracted to mulch. They may feed on mulch if and only if they are already present, but termites prefer better quality, wood-like construction debris buried in the backfill. Pine bark and cypress are the least attractive to termites.
Myth: Freshly chipped wood will “suck” the nitrogen out of the soil.
Not so. Nitrogen does not move up into the mulch, and mulch sitting on the soil surface will not take large amounts of nitrogen from the soil. However, Fountain does note that organic matter like sawdust, when incorporated into the soil, can tie up significant amounts of nitrogen. Over time, as it decomposes, compost and mulch will actually release nitrogen and other mineral elements for plant use.
Myth: If some mulch is good, more must be better.
Three inches of mulch is all that you need on the soil surface; two inches if you are using a finely ground mulch. Any more and you negate the benefits of mulching since excess mulch keeps oxygen and water from getting to the plant roots and causes roots to grow up into the mulch.
Myth: Piling mulch against a tree will protect the trunk.
For some reason, it has become popular to pile mulch up against tree trunks. Known as “mulch volcanoes,” this practice is not only extremely unattractive, it is also bad for the tree. Mulch piled against the trunk will keep the trunk moist, causing the bark to decay. The moist trunk is a more attractive food source for mice, insects and fungi. Mulch should not touch the tree – keep it four inches from the trunk.
Myth: You need to add fresh mulch every year.
Freshly applied hardwood mulch looks dark and moist, a look that many of us find very attractive. But this look doesn’t last very long. Many people add more and more mulch, year after year, until the layer is much too thick. Remember, too much mulch negates many of the benefits of this practice.
You only need to replace mulch if it has completely broken down. The amount of time this takes varies with the type of mulch. Always check the depth of the mulch before adding more.
If you loosen the surface of the existing mulch with a cultivator, this will freshen its appearance. However, if you insist on adding new mulch every year, then it is important to remove the existing mulch first in order to avoid excessive depth. If you remove the mulch before it rots, however, you are also taking away the potential for adding nutrition to your soil and improving soil texture.
Myth: Placing landscape fabric under the mulch will make your mulch last longer.
You actually want the mulch to break down and slowly become incorporated into the soil. Decomposed mulch improves drainage in heavy clay soils and helps retain moisture in sandy soils.
Landscape fabric (aka “weed mats”) do not prevent weeds from growing. In fact, this product just makes the weed situation worse. As the mulch rots, it creates soil. The weeds seed then germinate in this soil and the resulting weeds root into the landscape fabric and become much more difficult to pull out. Many weeds, such as Bermudagrass, nut sedge and others, will push up through the fabric. Good advice: Don’t use landscape fabric in your garden beds.
Mulching is a beneficial practice, but only if we lay these myths to rest.