Four helpful hints pertaining to garden mulch

FALLBROOK – Most gardeners know that mulching trees, shrubs, and flower beds is a good practice, even if they may not know all the reasons. Beyond the obvious advantage of its decorative use to make plantings look clean and attractive, there are real environmental benefits that can also help gardens reduce maintenance and protect every homeowner’s investment in time and plant materials.

Weed Control

Most homeowners understand mulch helps reduce weeds, but best results depend on understanding why. Weeds need sunlight to germinate in the soil. Proper use of mulch will serve as a barrier to sunlight and can help decrease the germination of weed seeds. Use a shredded hardwood or softwood material at a depth of at least two to three inches for best effect.

Hint: Those who prefer the more rugged look of larger particles like mini nuggets or nuggets should use a one-inch layer of shredded material first and then place a two-inch layer of larger materials on top to get the advantages of both materials.

Erosion Control

Mulch is often used by highway departments to help stabilize roadside embankments from erosion. The same principle applies to home gardens and the same guidelines pertain. Slopes create collection points and water flows that can carry soil downhill. The same is true of large-particle wood mulches. Since wood products often float, large particle mulch may flow downhill in a significant rainfall.

Shredded hardwood mulches should be used to stabilize slopes. These materials are more dense and tend to mat together. In lighter rainfall, most shredded mulches will trap and absorb moisture thereby preventing its collection and runoff. In heavier rainfall, the intertwined particles of a hardwood mulch hold the material together.

Hint: Unfortunately, a torrential downpour on a steep incline may create more force than even the best mulch can resist, so, the steepness of the slope and the frequency of torrential rains must be considered when selecting mulch options. An inorganic mulch like rock or stones may be the best option, especially for areas too steep to maintain plants.

Moisture control

On the opposite extreme from torrential rains is drought, and once again, mulch can provide needed protection for landscape plants. As a wood product with a large surface area compared to its size, mulches can absorb a significant amount of water. That retained moisture, which is released over time, can reduce the need to water plants during a drought. Even more important is the ability of mulch to allow water to penetrate to the ground while forming a barrier to reduce evaporative losses under the sun.

Hint: Retaining existing moisture is just as important to reducing water use as is the retention of new moisture. Maintain a two- to three-inch layer of loose fill mulch to allow moisture access from the top and prevent moisture loss from beneath.

Temperature control

Excessive heat in the soil can damage plant roots, kill beneficial bacteria and deactivate slow release fertilizers. A two- to three-inch layer of any organic mulch can reduce the soil temperature around plant roots. In colder climates, a good mulch layer can insulate the soil from excessive cold protecting the roots from freezing. Mulch can also be piled around tender plants in a freeze.

Hint: Do not leave the mulch on above-ground stems for long in warm weather. The added moisture and heat can encourage insects to attack the stems. During the growing season, keep mulch one inch from the base of shrubs and trees.

The Mulch & Soil Council is the national trade association for producers of horticultural mulches, consumer potting soils and amendments and commercial growing media. For more information, see http://www.mulchandsoilcouncil.org.