Proper Mulching & Soil Treatment
As beneficial as mulch is, too much can be harmful. The generally recommended mulching depth is 2 to 4 inches......
Add content hereTrees growing in a natural forest environment have their roots anchored in a rich, well-aerated soil full of essential nutrients. The soil is blanketed by leaves and organic materials that replenish nutrients and provide an optimal environment for root growth and mineral uptake.
Urban landscapes, however, are typically a much harsher environment with poor soils, little organic matter, and big fluctuations in temperature and moisture. Applying a 2- to 4-inch layer of organic mulch (such as that offered by Owen Tree Service) can mimic a more natural environment and improve plant health.
Benefits of Proper Mulching- Proper mulching reduces the germination and growth of weeds.
- Mulch serves as nature's insulating blanket, keeping soils warmer in the winter and cooler in the summer.
- Many types of mulch can improve soil aeration, workability, and drainage over time.
- Some mulches can improve soil fertility.
- A layer of mulch can inhibit certain plant diseases.
- Mulching around trees helps facilitate maintenance, and can reduce the likelihood of damage from "weed whackers" or the dreaded "lawnmower blight".
- Mulch gives planting beds a uniform, well-cared-for look.
As beneficial as mulch is, too much can be harmful. The generally recommended mulching depth is 2 to 4 inches. Unfortunately, North American landscapes are falling victim to a plague of over mulching. A new term, "mulch volcanoes", has emerged to describe mulch that has been piled up around the base of trees.
Most organic mulches must be replenished, but the rate of decomposition varies. Some mulches, such as cypress mulch, remain intact for many years. Top dressing with new mulch annually, often for the sake of refreshing the color, creates a build-up to depths that can be unhealthy. Deep mulch can be effective in suppressing weeds and reducing maintenance, but it often causes additional problems.
Problems Associated with Improper Mulching
- Deep mulch can lead to excess moisture in the root zone, which stresses the plant and may lead to root rot.
- Piling mulch against the trunk or stems of plants stresses stem tissues, and may lead to insect and disease problems.
- Some mulches, especially those containing cut grass, may affect soil pH.
- Continued use of certain mulches over long periods of time leads to micronutrient deficiencies or toxicities.
- Mulch piled high against the trunks of young trees creates suitable habitats for rodents that chew bark and girdle trees.
- Thick blankets of fine mulch can become matted, which prevents the penetration of water and air. In addition, a thick layer of fine mulch evolves into potting soil that supports weed growth.
- Anaerobic, or "sour", mulch gives off pungent odors, and the alcohols and organic acids that build up may be toxic to young plants.
Proper Mulching
It is clear that the choice of mulch and the method of application can be important to the health of landscape plants. The following are some guidelines to use when applying mulch:
- Inspect plants and soil in the area to be mulched.
- Determine whether drainage is adequate.
- Determine whether there are plants that may be affected by the choice of mulch. Most commonly available mulches word well in most landscapes.
- Some plants may benefit from the use of a slightly acidifying mulch such as pine bark.
- If mulch is already present, check the depth. Do not add mulch if there is a sufficient layer in place. Rake the old mulch to break up any matted layers and to refresh the appearance. Some landscape maintenance companies spray mulch with a water soluble, vegetable-based dye to improve the appearance.
- If mulch is piled against the stems or tree trunks, pull it back several inches so that the base of the trunk and the root flare is exposed.
- Organic mulches are usually preferred over inorganic materials due to their soil-enhancing properties. If organic mulch is used, it should be well aerated and, preferably, composted.
- Avoid sour-smelling mulch.
- Composted wood chips can make good mulch, especially when they contain a blend of leaves, bark, and wood. Fresh wood chips may also be used around established trees and shrubs. Avoid using uncomposted wood chips that have been piled deep without exposure to oxygen.
- For well-drained sites, apply a 2- to 4-inch layer. If there are drainage problems, a thinner layer should be used.
- Avoid placing mulch against the tree trunks
- Mulch out to the tree's drip line or beyond.
The root system of a tree is not a mirror image of the top. The roots of most trees extend out a significant distance from the tree trunk. Although the guideline for many maintenance practices is the drip line - the outermost extension of the canopy - the roots can grow many times that distance. In addition, most of the fine, absorbing roots are located within inches of the soil surface. These roots, which are essential for taking up water and minerals, require oxygen to survive. A thin layer of mulch, applied as broadly as practical, improves soil structure, oxygen levels, temperature, and moisture availability where these roots grow.
Remember: if the tree had a say in the matter, its entire root system, which usually extends well beyond the drip line, would be mulched.
(Taken from the brochure "Proper Mulching Techniques", ©2002 International Society of Arboriculture.)
Wednesday, December 31, 2008, hans