IN THE GARDEN Q&A: VALLEY FROST, AVOCADO CARE.

Byline: JOSHUA SISKIN

Q: I was wondering if you could provide some information about dealing with our frost. I'm not sure when and how far to cut back the plants that have been affected, specifically my lantana and bougainvillea. Also, how do I know if the plant is a goner?

-- Jane McPherson,

West Hills

A: I would not do anything for another month. In the Valley, March 15 is generally considered to be the last day that a frost or a freeze could hit. However, I remember one year when a frost occurred a few days later so, just to be safe, I would wait until the official arrival of spring on March 21 to remove dead growth.

By March 21, barring another freeze before then, you will have seen where new growth is going to occur. By that time, small green shoots will have sprouted from all viable stems and branches of tropical and subtropical evergreens such as bougainvillea and lantana. Any branches without new growth may then be pruned back. Keep in mind that certain deciduous shrubs and trees, such as crape myrtle, do not leaf out until late spring so do not be alarmed by their lack of new growth.

It often happens that green shoots and leaves will sprout from the lower parts or bases of cold-damaged stems or branches, while the upper parts will not recover. In such cases, cut back to the uppermost new shoots.

Q: I have a very healthy avocado tree about 15 years old. We just finished picking it clean and enjoyed about 50 avocados this year. I would like to do a light pruning and take 8 to 10 inches off the lower branches that have grown over my driveway. However, I heard that avocado trees should not be pruned. Is this true? I would also like to know the best product to use to fertilize my tree.

-- Craig Wendel-Smith,

Sunland

A: As a rule, avocado trees should not be pruned, but a very light pruning, once danger of frost is over, should not damage them. Where you have an avocado tree growing in your front or backyard, the only reason to prune is to keep lower branches 6 feet off the ground so that squirrels cannot jump into the tree and munch the fruit. Avocado trees are extremely sensitive to heavy pruning and have a tendency to die back from where saw cuts are made.

Fertilization of avocado trees is an afterthought, as they are not heavy feeders. More important to their health is a thick layer of mulch constantly maintained over their shallow and disease-prone roots.

An organic fertilizer with a 7-4-2 analysis, representing percentages of nitrogen, phosphorus and potassium, respectively, is recommended. The blend contains a mixture of bone meal, feather meal, kelp and several other ingredients. You can find this formulation, including beneficial mycorrhizal fungi, under both Whitney Farms and Dr. Earth labels. In general, any fertilizer designed for citrus can be effectively applied to avocado trees as well.

Avocados have been described as the ideal urban and suburban trees for Sun Belt states. They are surprisingly resistant to pollutants and free of pests. They are large trees, creating abundant shade, but pretty much take care of themselves. In our area, they should not be planted north of Granada Hills due to their cold sensitivity. To keep squirrels away, their branches should be kept 6 feet from structures and their trunks wrapped in tin.