Mulching 101

Phillip Peters
Adams County Master Gardener

If there was ever a time to apply mulch to the garden, it is now. The continuing drought conditions show little sign of improving measurably. Even if the water situation does improve, the hot summer sun makes demands on our garden plants that cause them considerable stress.

Putting a good application of mulch on the beds accomplishes several things that cut down on stress. A layer two to four inches thick will keep soil cool, as the air trapped in the mulch insulates the ground. It also prevents soil from being splashed onto the plant leaves, thereby reducing the incidence of fungal diseases and unsightly dirt on the plant. Applied evenly, it provides a neat and pleasing look to the garden. Most importantly, a mulch layer helps the soil retain any moisture that does fall, since the same trapped air that acts as an insulator is also a poor conductor of heat that would dry out the soil. Not only are the plant's roots cool, very important for plants such as clematis, but they remain moist.

If you are like me, a trip to the garden supply store overwhelms you. There is mulch and more mulch. There is organic mulch, derived from something that was once alive and inorganic mulch made from inert stone or various synthetic materials. There is mulch in bags and piles and plastic mulch in rolls. And they come in many colors and textures: black, brown or red shredded bark, large chunk bark, stone and brick chips in light reds, dark reds, various grays, black and basic white to suit every need and aesthetic taste. How to choose?

You might start by deciding whether you want organic or inorganic mulch. Organic mulches such as bark, shredded bark, peat, compost or leaf mulch convey a warmer, more inviting feeling because their colors and textures are less formal.

Organic mulches are made from natural materials: wood chips, shredded bark, coconut fiber, paper, and leaves among others. Their textures vary from coarse to fine and, depending on which you choose, evoke different emotional responses. Make your choice to fit your artistic vision. As these mulches break down, they contribute nutrients and bulk to enrich the soil. To prevent a water-repellant crust from forming on the top on the finer materials, rake them occasionally and renew the top several inches periodically.

Examine the finer shredded bark mulches periodically for signs of bird's nest fungus. This is a growth that forms colonies of bird-nest-shaped cups in which are egg-like fungal sacks full of spores. As these spread, they make the bed look unsightly. A related fungus, called artillery fungus, looks similar, but, as the bodies open, they can shoot spores up to 30 feet. They can spot house siding or a car parked in a driveway. Remove any affected areas of mulch immediately and dispose of them.

Inorganic mulches offer a selection of stones, gravel, lava and brick chips. By their very nature they convey a sense of endurance and permanence. Properly maintained, they call attention to a beautifully manicured, formal bed. They are most effective in a bed of perennials and shrubs that will not be moved or disturbed often. Planting annuals in this material will leave traces of dirt and signs that the soil was disturbed, sometimes scattering the material, and detracting from the neatness you are trying to achieve. But, if you are trying to set a formal tone for your garden, by all means, use one of these.

Remember that lighter colored materials will reflect the sun's light and may burn leaves that hang too low. Stone and brick also retain heat. A benefit in winter when stone absorbs the day's heat and releases it gradually during the cold winter nights, this could be a drawback in summer, depending on where the garden is situated and how much sun it gets. Small plants and new plantings are more susceptible than large and mature ones.

A word about using roll plastic as mulch. Keep in mind that, while it retains moisture, it also prevents water from penetrating the soil except where there are holes for the plants. A plant's natural cycle is to use water that falls from all its leaves, all the way out to its drip line. Its roots are expecting this. Consequently, under plastic it may not get enough water. And, if you don't cover the plastic, the material may reflect the sunlight onto the leaves and cause sunburn.

On the positive side, the color of the plastic can influence crop yields. Red will help increase your tomato crop, while white plastic can increase productivity up to 30%. Be careful with the clear plastic. It acts as a mini-greenhouse. It is used to increase soil temperature but will not kill weeds as you might think.

The best way to weed mulched beds is by hand. Since the material retains moisture and is not compacted, weeds will usually pull out without difficulty. Mulch the bed to a depth of two to three inches, a bit more if you are using coarse bark mulch. Avoid the tall, volcano shaped mounding around trees that seems so popular today. This invites insects, disease, fungus and small rodents.

Be sure to keep mulch several inches away from trees, shrubs and flowers. Mulch that is too close can create favorable conditions for disease or insect activity. It can also provide shelter for rodents that can ring the bark of a tree or shrub or devour a plant stem.

Applied carefully and maintained regularly, mulch will beautify your garden while it keeps it moist, nourishes it, and makes it easier to care for.

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