Q: I have a 'Variegated Pink Eureka' lemon tree, about 4 feet high, in a big container. It bloomed recently (some blossoms are still on) and began to set tiny fruit. But now I'm worried: Some of the baby lemons have dried out and turned brown. Is there a typical cause of this, and how can I prevent it? The tree seems robust, and gets regular water and lots of sun. I bought it at Costco and potted it in February.

A: Because you say your lemon tree looks good otherwise, it probably has normal fruit drop. Fruit trees of all kinds generally have more flowers or small fruits than they can ripen. It is typical for lemons, including the lovely 'Variegated Pink Eureka,' which has striped fruit with a pink interior, to lose 70 to 80 percent of their flowers before they set fruit, then to lose a few more fruits while they are tiny or up to golf-ball size.

If a tree is bearing very lightly or not at all, this could be due to lack of bee activity (for pollination), soil infertility, irregular or excessive water, sudden shifts of temperature or humidity, or insect infestations. While I think your tree is healthy, do consider if it is overwatered. While citrus in containers will need water more often than it would in the ground, you should water only when the top 2 inches of potting mix is dry, then water until the pot drips from its drainage hole. If you are not already doing so, purchase a citrus fertilizer and apply according to the directions for citrus in a container.

Q: My cherry tree is an enigma in that it has been growing very quickly for almost two years yet has never had a cherry. Another cherry tree which I planted later, and is much smaller, looks healthy but does not have any fruit either. I assumed they would pollinate each other, but it didn't happen. I live near Stanford University.

I water the base of the cherry tree every other day or thereabouts. I don't run the water too long (more than a few minutes), and I follow the same watering procedure for the smaller cherry tree.

Most of the plants I have lost this summer were a result of poor drainage, so I hope this larger tree is not going to suffer the same fate.

A: I think your cherry trees aren't bearing because they are too young. The average age for a full-size sweet cherry tree to bear is four to six years. (For dwarf sweet cherry trees, the average age is three to four years.) If you were near the coast, I'd guess that your microclimate didn't suit cherries, but your somewhat inland location should allow sweet cherries to bear fruit.

You are right that most sweet cherries require a pollenizer, a nearby tree to provide cross-pollination. (A good choice is 'Stella,' which is self-pollinating and pollinates most other varieties well. Two dwarf varieties, 'Minnie Royal' and 'Royal Lee,' cross-pollinate each other.) However, even the right pollenizer won't help if the trees are too young.

You should indeed worry about your cherries if you have lost other plants to poor drainage. Soil that is wet too often is a common reason for tree death, and cherries are particularly susceptible.

The reason poor drainage kills plants is that the roots must have oxygen. If the soil is constantly wet, roots drown. Moreover, the gasping roots are susceptible to fungus and bacteria, which often kill the plant.

It sounds like you are hand-watering your trees - and doing it much too often. Insert a moisture meter in the soil a foot or two from your tree. If the soil is wet from the top to a foot down, don't water. Wait until the top 2 inches are dry. When you water, do so for at least a half hour, then do not water until the top 2 inches are dry again. Water not at the trunk, but at the drip line, below the circumference of the outermost branches.

If you use drip irrigation, put a ring with the emitters 12 inches apart around the drip line. Seek timing advice for your tree sizes and soil type from a drip irrigation store or from the UC Davis Home Orchard website (http://bit.ly/MqG1VG).

Do not water your trees in the winter rainy season.

Because you are worried that your garden's drainage is poor, you may want to hire an irrigation specialist to investigate and see if installing drainage pipes will solve the problem.

Pam Peirce is the author of "Golden Gate Gardening" and blogs at http://goldengategarden.typepad.com. Send garden and plant-related questions to home@sfchronicle.com.