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Garden Q&A

A Bright Idea for Ridding Soil of Algae


Question: What can I do about the green color showing up on the soil in my yard? It is quite pervasive. Is there anything I can do to help the soil? Also my yard is quite shady, so how much should I water?

--E.C., Encino

Answer: You have almost answered your first question with the second, by mentioning how shady your garden is. The green color on your soil is not a moss, but an algae, similar to the algae that grow on the sides of trees and flowerpots--microscopic organisms lacking roots, stems or leaves.

Though it is said that wettable sulfur or copper fungicides will control algae on trees and soil, I am unaware of any product being labeled for that use, and treatments will have only temporary effects anyway.

In the shady glades at Descanso Gardens, in La Canada Flintridge, they throw down sand to keep algae-covered paths from becoming slippery, but otherwise "consider it a beautiful part of a cool, moist garden," said director Richard Schulhof. It certainly won't hurt the soil, or the bark of trees it grows on.

To get rid of algae on soil, you must make the area brighter and drier. Frequent, short irrigation (or winter rains) bring on algae, as does too much shade. Pruning and thinning the vegetation overhead will let in more light; breaking up and loosening the soil with a long-handled, pronged cultivator will help dry out the soil.

Irrigating less often, but perhaps for longer intervals, will help keep the soil surface dry. Shaded areas generally need less water, unless the shade is being cast by a tree. Tree roots are greedy and other plants will get very little. You'll need to water for longer periods of time if trees and plants are to get enough. Frequent, shallow irrigation only wets the soil surface and helps only the algae.

I can't give you specific information on watering since it varies so much from area to area, from soil type to soil type, and even within the garden. Until you get a feel for the garden's water needs, it's important to check the soil with a spade or trowel to see when it is almost dry and needs irrigation.


Q: What is wrong with my roses? They grow and bloom well but when I put them in vases, they do not open all the way but die partly closed.

--C.L., Chatsworth

A: To open properly, the cut rose needs to keep growing, so requires water and nutrients. To assure a ready supply of both, follow this advice:

Cut early in the morning or late in the evening with sharp shears. Immediately put stems in a pail of warm (110-degree) water. Bring inside and cut the stem again, this time making the cut under water. This prevents a little bubble of air that can block the water uptake.

Put a commercial preservative in the vase water, or add one-fourth teaspoon household bleach and 1 1/2 teaspoons sugar to each quart of water. Or add a non-diet, citrus-flavored, carbonated drink, such as 7-Up. Any of these provide nutrients and prevent bacteria from blocking the uptake.

If you do not use a preservative, you should change the water every day.


Q: I propose supplementing the watering of my citrus trees using gray water. The water will come from the shower and bathroom sink. Is there any downside to this proposal and can you suggest a disinfectant I should add to the holding tank?

--R.W., Los Angeles

A: Though technically governed by what many consider burdensome, expensive and questionable codes, using gray water from the shower and bathroom sink shouldn't pose any problems, according to Robert Kourik, author of a pamphlet called "Gray Water Use in the Landscape" ($6--which includes tax and postage--from the author, P.O. Box 1841, Santa Rosa, CA 95402, (707) 874-2606).

However, he cautions against holding tanks that can become "smelly and septic." Let the gray water run straight into the garden and keep moving the hose around so gray water can't puddle. There is no such thing as a "disinfectant" for gray water and it's not needed, as long as the water soaks into the ground.

Water from the shower and sink is slightly alkaline, but a good soaking every few years from rains or municipal water should flush out excess alkalinity. Kourik likes to keep a 3- to 5-inch-thick mulch on areas being irrigated with gray water.


Q: We live in Venice about a mile inland and have been considering the 'Zephirine Drouhin' climbing roses for the north wall of our house. It's described as being shade tolerant. Do you think this rose would work on this wall and if not, what would you recommend as a good flowering climbing plant for a north wall?

--G.T., Venice

A: I grew the oddly colored Zephirine several miles from the coast and it did poorly. Sharon Van Enoo, a Torrance Rosarian says it "mildews badly" near the coast and isn't a particularly good rose anywhere in the Southland. The Huntington Library rose garden took its out, but you can still see them growing as shrubs at Descanso Gardens in La Canada Flintridge.

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