Mulch

Applying mulch may be one of the simplest elements of working ina garden, but a Penn State horticulture specialist says there's a lot more to itthan just dumping a bag of mulch around plantings.

Aside from its benefits to plants, mulch can be part of the landscape design,with gardeners choosing a variety mulches for texture and color. Most mulchesare comprised of hardwood bark, cypress bark, bark nuggets, wood chips or othermaterials. Robert Nuss, professor of ornamental horticulture at Penn State'sCollege of Agricultural Sciences says landscapers don't need to be concernedabout decomposition, compaction resistance and other factors if the mulch ispurely ornamental. Landscapers who create large mulched areas with no plantswithin a garden may want to lay a covering of landscape fabric or plastic on thesoil to control weed growth.

However, if you a mulching around plants, Nuss suggests you follow a fewsimple rules that will improve the overall health and growth of the plants.

Nuss suggests choosing a mulch that features:

• Consistent color and texture
• Compaction resistance
• Wind and water erosion resistance
• Slow rate of decomposition
• Ability to reduce weed growth.

All mulches must allow an exchange of gases -- oxygen into the soil andcarbon dioxide out of the soil -- as well as water penetration into the soil,Nuss says. A coarse-textured mulch will enhance both gas exchange and waterpenetration. If your choice of mulch slows or stops these processes, plants willdecline and die.

Most mulches should be just two to four inches deep, Nuss explains. Gardenersshould use the low end of that scale on heavy clay soils, and the upper end ofthe scale for loose, sandy soils. Too much mulch smothers the roots by reducinggas exchange, he says. Deep layers of mulch also will absorb all the water fromlight rains, holding it well above the root system.

Mulch also has these benefits:

• Moisture conservation. If mulch is applied correctly, soil water evaporates slowly, giving plants a consistent moisture source.  As the mulch breaks down, the soil's ability to hold water may improve. Mulched plants always will survive a drought better than plants that have not been mulched.
• Water Infiltration. Mulch cushions the impact of raindrops against the soil surface, allowing water to gently flow into the soil. When rain falls on bare soil, it disrupts the soil structure at the surface and causes a certain amount of compaction. By slowing down the inward movement of water, mulch reduces soil erosion.

Nuss warns that gardeners should not pile mulch on plants indiscriminately,particularly around the trunks of trees or shrubs. Mulching against a tree trunkcan cause bark decay and other problems for the tree or shrub.