Mulch Improves Garden Beds

By Joel M. Lerner
Saturday, December 27, 2008

Mulch is a gardening mainstay because it protects and nurtures plants while improving the look of many landscapes. Plants need different types of mulches depending on the season.

There are many materials to pick among: bark chips, shredded bark, salt hay, shredded wood in natural colors or dyed (usually black, brown or red), gravel, shredded recycled rubber from tires, shells, pine needles and peat moss. You can even use ground corn cobs, cocoa mulch (unhealthy for dogs), or licorice root, which is a rare find, but very fluffy, dark and handsome.

I suggest avoiding stone as mulch on planting beds because of the difficulty of getting to the earth. You can't work compost into soil with a rock coating over the surface, so plants are deprived of the ongoing replenishment of organic material. And because organic material is the most difficult element to retain in the soil, you want to be able to add more.

Because it doesn't decay, though, ornamental stone mulch is helpful for covering problem areas such as compacted soil resulting from heavy foot traffic. It can also provide color in the garden when used in grays, tans, pinks, reds, blues, browns or shades of black, and is available in sizes ranging from pea-sized to three to four inches in diameter. Blow off leaves and debris when it gets dirty and freshen with new stone. If you choose this maintenance technique, start with a fairly thin layer, one inch or less, because the depth will increase over the years as you add fresh stones. Be sure to lay the rock over a strong, porous, nonwoven landscape fabric.

To mulch with biodegradable materials, try newspaper two to three sheets thick. This recycles paper and replaces landscape fabric. The Washington Post, for example, is considered 99.9 percent biodegradable. The ink is carbon black-based and safe, and the color inks are soy based. When paper decays, it can be tilled into the soil. Use this process when preparing beds for planting in spring. Lay an inch or two of compost or leaf mold over the newspaper to hold it in place and speed its decay.

For winter, compost is excellent mulch, as are the leaves that fall into the bed, as long as they aren't piled too thick. Leaf mold (partially composted leaves) is good winter mulch, too. It is best composted for a season so it can decay, but you can chop stems and leaves with a string trimmer, or rotary mower on its highest setting, and let the material decay where it falls. The leaves that drop are some of the best nutrients for the plants that grow under them.

So, should you mulch your plant beds? Yes. Does all mulch offer the same value? No.

Shredded wood and bark mulches can mat together, repelling water and discouraging air circulation to the roots of plants. They can, however, protect the roots and stems that are tender to freezing temperatures. Organic mulch can be laid over stems of tender plants, such as roses, as high as it will pile -- 12 inches or more, provided it is removed before growth begins in spring. And a two- to four-inch covering of mulch will offer winter protection for tender bulbs and perennials.

The most beneficial material would be utilitarian organic mulch to condition the soil as water and air percolate through it. This should be partially to fully decomposed so it doesn't mat together, inhibiting percolation of water and circulation of air. This can be done anytime the weather is pleasant and soil isn't frozen or soggy. Rich, friable, composted organic mulches condition the earth as organisms in the soil break them down.

Leaf mold and compost are easy to get in this region, which has lots of leaves to grind and compost. If there aren't enough leaves for all the planting beds, supplement them with Leafgro. It is a rich, dark mulch made entirely of composted leaves. These materials will enrich the soil as they work their way into the beds.

Compost helps discourage many root rot diseases and drainage problems. When the soil isn't frozen, digging liberal amounts of compost into the earth around a plant's roots applies compost as fertilizer, adds moisture-holding ability and improves aeration.

Where the soil is bare and lacks plants or roots, you can mulch the soil by digging three inches of compost on the surface into eight to 10 inches of dirt. That is winter mulching that will pay off next summer.

Another practice for incorporating compost around an already installed plant is called vertical mulching. Dig holes with a manual posthole digger or excavate a trench six inches wide and eight to 10 inches deep around the outside branch spread (drip line) of a plant. Fill the holes or trench with compost. The deeper you vertically mulch, the better.

There are other options for mulch that can be used now to enrich the soil for spring. These can be incorporated into the soil as nutrients. Annual rye or hairy vetch planted now can be dug under in spring. Other options are mychorrizae, animal manure from the zoo, stable or barn (be sure to compost horse manure), and seaweed or fish-based products, which are considered to be some of the most nutrient-rich, natural growth stimulants you can use in your garden.

Do this preparation in winter during temperate weather when conditions aren't soggy, and the organic material will be in the bed ready to be cultivated or dug into the soil in spring.

A good ornamental mulch to use during the growing season is two to three inches of leaf or garden compost with about a one-inch veneer of any organic mulch that you think is aesthetically pleasing. This way you achieve multiple benefits: nutrient production, moisture holding, soil conditioning, weed control -- and good looks.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site,

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