By Jeff Floyd
Certified horticulturist and arborist
Soil compaction is the enemy of all landscape plants. Roots take up water, nutrients, and oxygen from the soil. They also use it to anchor themselves in place against strong West Texas winds. But when soil is crushed by repeated vehicle or foot traffic, individual soil particles are squeezed closer together. The smaller space between particles means there is a lower capacity for soil to hold air and water. Dense soils are also more difficult for roots to penetrate. Without the ability to sufficiently grow into the soil, plants may eventually lose their anchorage as they grow larger.
Compacted soils are a notorious problem on construction sites. Landscapes are almost always installed at the conclusion of a construction project. The rapidly growing cells at the tip of a root are incredibly strong but not strong enough to pry apart a heavily compacted soil. Sometimes plants will linger for years under the pressure caused by compaction. Topdressing the site with loose soil does not solve the problem.
So how are dense soils broken up? Lawn aeration, vertical mulching and the addition of organic matter can help correct soil compaction, although these practices won’t take effect overnight. Aeration requires special equipment which lifts plugs out of the soil. The three to four-inch holes left behind are sometimes filled with organic matter but that isn’t necessary. Leaving the holes open allows air and water to move closer to the roots. When aeration is performed two or three times per year, some compaction is lessened.
Vertical mulching makes use of an auger to drill holes that are around two inches wide and four to six inches deep. The holes are then backfilled with a porous material such as sand or compost. This is a labor-intensive project that may run the risk of damaging irrigation or the roots of trees.
Incorporating any amount of organic matter into soil brings it to life. Including it with aeration or vertical mulching practices will increase the rate at which compaction is relieved. Nevertheless, compaction problems will take a long time to improve even when these methods are employed.
A better way to minimize compaction is to limit the amount of traffic that moves over the soil in the first place. Develop a plan to protect the soil around trees before construction begins. Ensure your contractor is on board with protecting high-value plants. You, your contractor, and your plants will benefit.
