QUESTION: I plan to use the shredded wood that the city collects when its workers trim city trees. It's free! But I have read it's unwise to put "untreated wood products" on the ground because they attract termites and other pests. Do you have any advice on treating wood used as a mulch and do you feel using it is a risk?
--D.H., Moreno Valley
ANSWER: The benefits of using organic mulches far outweigh any problems.
They inhibit weeds, conserve moisture, moderate soil temperatures, reduce erosion from irrigation and rain, improve the soil structure and--eventually--add nutrients as they decompose. And you have access to the best kind of mulch--shredded tree trimmings.
Considerable research has been done on mulches at the Ventura County Cooperative Extension. Researchers found that the source of the wood mulch is of minor importance. Even eucalyptus works fine.
However, mulches do attract bugs. "They're broiling with them," said farm advisor Ben Faber, who participated in the research. This is not a bad thing and is necessary, in fact, if the mulch is eventually to break down.
What you want to do is use mulches around permanent plants and not near temporary plants such as lettuce. These little creatures--like slugs, pill bugs and earwigs--eat only soft-leaved or decaying plants. They'll do little or nothing to permanent garden fixtures, such as perennials, shrubs and trees.
In my own mulched garden, only the tiny slugs are any problem and only on some vegetables that happen to be in raised beds surrounded by mulched paths. In the Ventura County experiment, researchers found that rough mulches actually discourage snails.
I have never heard of mulches attracting termites.
"Untreated" means that wood mulches have had no nitrogen added to them, and this is perhaps what you were reading about. Incorporated into the soil, wood products tend to steal nitrogen from the soil to use in the decomposition process, unless they have been "treated" with added nitrogen.
But if the mulch is lying on the surface, it will not steal much, and this is easily compensated for by sprinkling a little fertilizer on top. Use an inexpensive, all-purpose granular fertilizer and, by all means, take advantage of that free mulch.
Dwarf Avocado Variety Available at Nurseries
Q: I'm thinking of taking out an old avocado tree that seldom fruits but shades my whole garden. I can't even grow impatiens underneath. Are there dwarf avocados, like dwarf citrus, that wouldn't take up so much room?
--C.L., Los Angeles
A: Nurseries sell an avocado called "Littlecado" that is supposed to be a dwarf. It is also sold as "Minicado," "Dwarf" and (rarely) "Wurtz," which is its real name.
I have never seen one growing in a garden, but Julie Frink, who collects data on the remarkable collection of avocados growing at the South Coast Field Station in Irvine, tells me that the tree planted there is only 8 to 10 feet tall and that it's a "nice-looking little tree" with pendulous branches that droop to the ground.
Vince Lazaneo at the San Diego Cooperative Extension said the tree needs staking when young because it grows "almost like a vine."
Frink says that the fruits are quite large, averaging 10 to 20 ounces, that they become their ripest in August but that the taste is only of average quality, similar to a "Zutano" or a "Bacon," rather than a "Hass" or "Fuerte." One grower I talked to, Gerald Carne in Fallbrook, said that the UC-developed variety named "Gwen" is also a smaller tree. He never needed more than a stepladder to pick the highest fruit.
Questions should be sent to "Garden Q&A;" in care of the Real Estate section, Los Angeles Times, Times Mirror Square, Los Angeles 90053. Please include your address and telephone number. Questions cannot be answered individually.