I’ve heard that using mulch in my yard is helpful, but I don’t know what kind of mulch to use. Are there any materials I should avoid? —Want to Do It Right
Mulching helps hold moisture in the soil by slowing evaporation and by increasing the moisture-retaining ability of the soil itself. If you are using organic materials for mulch, they will add to the soil’s structure as they decompose, providing food for organisms such as worms. A thick layer of mulch also impedes the growth of many weeds. Mulch can be arranged in order to capture, direct, and hold rainwater, preventing stormwater runoff and preserving the water for your yard.
Many organic materials can be used as mulch. Some common mulches include wood chips and other green waste, such as shredded leaves, twigs, and straw; aged compost; and dried grass clippings. Lay down two to six inches of mulch, a thinner layer if using fine materials such as grass, a thicker layer if your materials are chunkier.
Mulch also makes attractive paths in the garden, reducing compaction of the soil. Inorganic mulches, such as rocks, can also benefit the garden by stabilizing soil temperatures and slowing evaporation.
One technique for rehabilitating a malnourished or weedy patch of earth is to sheet-mulch. First pull or cut weeds, then layer the ground with compost and wet it down. Cover the surface completely with sheets of corrugated cardboard or black and white newspaper, overlapping the edges of each sheet by several inches. Wet again with water, and finally cover with four to six inches of organic mulch. Over the next season or two, the cardboard will decompose, feeding the soil beneath.
Use recycled materials, such as trimmings from your own yard, your friends’ yards, or from a tree trimmer. Call to find out which ones offer this service, and whether they provide trimmings for free.
Don’t place mulch up against stems or trunks. Age compost before using it as mulch, whether green waste from yard and food scraps, or manure from livestock.
There are few don’ts. Don’t use cocoa mulch around pets. The theobromine in cocoa is toxic to dogs. Don’t dig woody mulches into the soil. Place them on the surface
where they won’t compete with the plant roots for available nitrogen. Don’t use trimmings from diseased plants or hay or other materials with a lot of seeds. (Rice straw does not contain seeds.) And don’t use mulch from far-away or virgin sources.
—Carrie Bennett, information services coordinator
There’s a set of large electric power lines running down my street. Is this is a health hazard? —Wary
The power grid that brings us electricity is made up of several parts: the generator plant; the extra high voltage lines that usually run in uninhabited areas; transmission substations situated closer to the service area; high voltage transmission tower lines (the kind you refer to); distribution substations; and distribution lines, the kind we usually see in neighborhoods. If you live near a substation or transmission tower line, you may encounter a heavy load of electromagnetic frequencies (EMFs), depending on how close you are and the amount of electricity running through the line. Power lines on the street can also carry a heavy load at peak hours.
The strength of EMFs falls off exponentially as you move away from the point source. It’s possible that any EMF you measure at your house from the high voltage power lines could be less than those from power lines coming into your home and wires running down your street. A Gauss meter can be used to measure EMF levels. Most utilities, including PG&E, will conduct EMF measurements for customers at no charge. Meters can be rented, and there are a few Bay Area companies that can be hired to take measurements and give advice.
Although controversial, measuring EMF levels is the best approach to determine the health impacts of living near the power grid, whether those are high voltage power lines, substations, or the wiring and appliances in your home. Most homes have a “normal” ambient level of .5 to .9 milligauss (mG). If Gauss readings are over 3 mG there’s a real problem. Quite a few studies have been done on occupational exposure to EMFs; adverse health effects include significant alterations in biological cycles, depressed levels of dopamine and seratonin, and depression. Other studies found links to childhood cancers, especially brain tumors and leukemia.
If high EMF exposure is suspected, move bedrooms away from point sources, especially children’s rooms. Be sure to use grounded appliances and situate electrical sources away from areas where the most time is spent. Avoid low-frequency (60 Hz) pulsating electromagnetic
fields such as those found in electric blankets and waterbed heaters.—Beck Cowles, information services program manager
