I have a plum tree that is 4 years old. Its trunk is approximately 4 inches in diameter. In the spring, it's loaded with blossoms. However, it has never had one piece of fruit. Any thoughts on what I can do to get some fruit?

– John P. Lane, Lincoln

According to UC Master Gardener Annie Kempees, fruit and nut trees normally begin to bear fruit two to five years after planting. That depends mainly on the species and method of training and pruning.

You mentioned that your tree produces many blooms yet does not set fruit. There are many reasons why this can happen.

There may be a lack of pollination by bees and other insect pollinators if the weather is too wet, cold or windy. Or it may be due to an absence of a pollenizer – another variety of plum planted nearby.

Frost during or shortly after bloom can cause young flowers, fruit or nuts to fall off the tree even though no frost damage can be seen.

If you expect a frosty night in early spring, consider covering your tree with landscape cloth or plastic and adding a heat lamp or old-fashioned "hot" Christmas tree lights under the cover.

This method can often protect early flowering and fruiting trees, providing temperatures do not fall too low and the cold weather is of short duration.

Leaves need six to eight hours of continuous sunlight per day for adequate photosynthesis for a tree to produce fruit. Lack of nitrogen can also lead to poor fruit set.

A lack of sufficient chilling hours for fruit set will harm the trees' ability to produce quality fruit.

Hardpan – compacted, impenetrable rock-hard soil – is often an issue as it does not allow for adequate water drainage away from the root system. Trees planted without sufficient amounts of good soil for their roots will languish.

If your tree is properly pruned, free of disease, sufficiently irrigated and fertilized, and has adequate sunlight but still fails to bear fruit after several years, think about grafting a different variety onto the tree, or replacing it entirely.

You can learn about grafting and plum varieties at the Fair Oaks Horticulture Center in Fair Oaks Park. The master gardeners' workshop schedule – including times to visit the center's demonstration orchard – can be found at http:// cesacramento.ucdavis.edu.

Do you need to have more than one tomatillo plant to get fruit? I've planted one plant in the past. It's grown beautifully and flowered profusely but never set any fruit. Do I need two for cross pollination?

– Roz Flynn, Camino

The tomatillo or husk tomato (Physalis philadelphica) is a cousin of the tomato cultivated in Mexico and Guatemala, says UC Master Gardener Dale Flynn. Its use in Mexico dates back to pre-Columbian times.

In several blogs about growing tomatillos, gardeners are reporting that their plants are healthy and growing well but are not setting fruit.

In these blogs, two suggestions appear over and over. First, the plant apparently does better the second year. And although there's no mention of needing cross-pollination, the successful reports all mention growing at least two plants.

The scientific community seems unsure. You don't have to have more than one plant for pollination, but you're more likely to get pollination and fruit set if you have more than one.

Edible tomatillos are annuals, so if your plant has been around longer than a season, it may not be the edible variety. As with tomatoes, blossom drop in tomatillos can be caused by a number of factors, including nighttime temperatures below 55 degrees, daytime temperatures above 90, smog, excess nitrogen, too much shade, or early blossoms that naturally fall off.

Some methods to help pollination include tapping on flowering branches when blooms are open or using a finger or brush to spread pollen from flower to flower.

To learn more, check "Specialty and Minor Crops Handbook" by Claudia Myers.GARDEN QUESTIONS?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.

Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put "Garden Detective" in the subject field and include your postal address. To contact your UC Extension directly, call:

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