Q. I need compost for my vegetable garden and fruit trees. I will also use some of it for flowers and shrubs. I have hard clay soil and will rototill in the compost to loosen the soil and provide nutrient amendment. My question is: Is compost containing biowaste safe to use for vegetable/fruit plants (i.e. safe for human consumption)? I am concerned about heavy metals, pharmaceuticals, toxins etc. migrating into the produce. Should I play it safe and just use regular compost (without biowaste)? What are the ingredients in regular organic compost? How much compost should be rototilled in? Is there anything else that needs to be added?”
– Ron Akutagawa
Shadow Hills
A. Biowaste, also called biosolids or sludge, is found in many of the bagged amendments and bulk compost mixes that are available throughout Los Angeles. In more than 25 years of gardening here, I have never seen research which showed that any local compost or soil amendment product, including those containing biowaste, carried dangerous amounts of any of the chemicals you mention. Whether sold in bags at a nursery or in bulk at a yard or composting facility, all local soil products, to the best of my knowledge, are safe for growing edible plants. However, to be completely sure that the product you wish to use is safe, send a sample of it to Wallace Laboratories in El Segundo for analysis.
Call 310-615-0116 or go to www.bettersoils.com for more information.
Any bagged or packaged compost or soil amendment product should have a description of its ingredients clearly labeled. A detailed chemical analysis is not provided but you can obtain such analysis by contacting the company that packages the product. You should know that even homemade compost, consisting of your own vegetable and fruit peels, coffee grounds, and garden debris, contains heavy metals such as lead, arsenic, and cadmium, albeit at non-toxic levels. These elements are present in every soil and, therefore, are found in the tissues of every plant. Incidentally, oleander prunings, which are highly toxic if ingested, should not go into a compost pile destined for the vegetable garden.
As a rule, you should apply a two-inch layer of compost to the soil surface prior to rototilling to a depth of 4-6 inches. Where a vegetable or annual flower garden is concerned, you really should improve the soil to a minimum depth of 6 inches for rapid growth and development.
Vegetable crops are seasonal and you want them to develop their edible roots, leaves, or fruits while the weather suitable for their growth still holds. If you plant late in the season – and you can still plant peas, cabbages, lettuces, and carrots – all the more reason to make sure that the soil is in perfect shape. Here, aeration is just as important as fertility.
Roots grow quickly in response to the abundant oxygen supplied by well aerated earth. Zealous gardeners excavate soil to a 12-inch depth before planting vegetables, although compost, amendments and fertilizers need not be incorporated deeper than 6 inches. If your soil is highly compacted with a texture of clay, you can also add gypsum, a product that looks and feels like flour, to the soil. In addition to softening soil and improving drainage, it also lowers soil pH, which is beneficial in our high pH soils.
Before applying gypsum, put on a dust mask or, alternatively, apply gypsite, a granular gypsum product that is easier to handle.Q. I need compost for my vegetable garden and fruit trees. I will also use some of it for flowers and shrubs. I have hard clay soil and will rototill in the compost to loosen the soil and provide nutrient amendment. My question is: Is compost containing biowaste safe to use for vegetable/fruit plants (i.e. safe for human consumption)? I am concerned about heavy metals, pharmaceuticals, toxins etc. migrating into the produce. Should I play it safe and just use regular compost (without biowaste)? What are the ingredients in regular organic compost? How much compost should be rototilled in? Is there anything else that needs to be added?”
– Ron Akutagawa
Shadow Hills
A. Biowaste, also called biosolids or sludge, is found in many of the bagged amendments and bulk compost mixes that are available throughout Los Angeles. In more than 25 years of gardening here, I have never seen research which showed that any local compost or soil amendment product, including those containing biowaste, carried dangerous amounts of any of the chemicals you mention. Whether sold in bags at a nursery or in bulk at a yard or composting facility, all local soil products, to the best of my knowledge, are safe for growing edible plants. However, to be completely sure that the product you wish to use is safe, send a sample of it to Wallace Laboratories in El Segundo for analysis.
Call 310-615-0116 or go to www.bettersoils.com for more information.
Any bagged or packaged compost or soil amendment product should have a description of its ingredients clearly labeled. A detailed chemical analysis is not provided but you can obtain such analysis by contacting the company that packages the product. You should know that even homemade compost, consisting of your own vegetable and fruit peels, coffee grounds, and garden debris, contains heavy metals such as lead, arsenic, and cadmium, albeit at non-toxic levels. These elements are present in every soil and, therefore, are found in the tissues of every plant. Incidentally, oleander prunings, which are highly toxic if ingested, should not go into a compost pile destined for the vegetable garden.
As a rule, you should apply a two-inch layer of compost to the soil surface prior to rototilling to a depth of 4-6 inches. Where a vegetable or annual flower garden is concerned, you really should improve the soil to a minimum depth of 6 inches for rapid growth and development.
Vegetable crops are seasonal and you want them to develop their edible roots, leaves, or fruits while the weather suitable for their growth still holds. If you plant late in the season – and you can still plant peas, cabbages, lettuces, and carrots – all the more reason to make sure that the soil is in perfect shape. Here, aeration is just as important as fertility.
Roots grow quickly in response to the abundant oxygen supplied by well aerated earth. Zealous gardeners excavate soil to a 12-inch depth before planting vegetables, although compost, amendments and fertilizers need not be incorporated deeper than 6 inches. If your soil is highly compacted with a texture of clay, you can also add gypsum, a product that looks and feels like flour, to the soil. In addition to softening soil and improving drainage, it also lowers soil pH, which is beneficial in our high pH soils.
Before applying gypsum, put on a dust mask or, alternatively, apply gypsite, a granular gypsum product that is easier to handle.

Q. What do you recommend planting as ground cover under a tree which is also shaded by buildings to the east and west? The buildings are two stories tall, about 20 feet apart. On another matter, I just returned from Guatemala where I was introduced to the beautiful tulip tree.
If I plant a tulip tree here, will it grow?
– Daria Chaikovsky
Sherman Oaks
A. If you are planting in deep shade, dwarf mondo grass is probably the best choice for a ground cover. Dwarf mondo grass (Ophiopogon japonicus) is actually a member of the lily family. It is closely related to lily turf (Liriope) but, unlike its cousin, does not attract snails.
It is an elegant plant that mounds up no more than four inches tall and consists of thin, fine-textured dark green leaves which produce a silky, glistening, and formal effect. Once established, it is rather drought tolerant. It may be propagated by division of established clumps.
If you have at least four hours of good ambient light, you can grow pink buttons (Polygonum capitatum). This ground cover is also drought tolerant and is distinguished by pink gumdrop flowers with burgundy stems, burgundy chevrons on the foliage, and burgundy leaf margins.
Although recommended for shade, its flowers and foliage assume deeper color with increased sun exposure.
Two tulip trees are seen in Los Angeles. I assume you are referring to the African tulip tree (Spathodea campanulata), since it is of tropical origin and would flourish in Guatemala. Its spectacular flowers are deep orange and resemble tulips. I have seen it growing in West Los Angeles but never in the Valley, where it may not survive due to our colder winters. The other tulip tree (Liriodendron tulipifera) is a magnolia relative. It is native to the eastern U.S., where it grows near stream bottoms and is accustomed to a steady supply of soil moisture. I have observed it growing in the Valley in Sherman Oaks and Woodland Hills, and it appeared to struggle in both locations. Its assets include clear yellow, tulip-shaped flowers and crown-shaped, deciduous leaves that turn color in the fall.