by Denise Levine, U. C. Master Gardener

The Napa Valley is known for its many varied microclimates. While some gardeners are blessed with perfect, protected spots for Meyer lemon, naval orange or grapefruit trees, others of us fail miserably at growing citrus.

If you are lucky enough to live in a spot that supports the needs of naval oranges and lemons, March is the month to plant them. But citrus appreciate year-round attention.

Now that our weather is getting warmer, some gardeners may notice fruit or bloom drop on their citrus. This is often triggered by hot, dry or windy weather but can be mitigated by consistent watering.

Each garden site will vary, but a general rule for citrus in the ground is a deep watering once weekly. In the Napa Valley, citrus do better with more frequent watering. Our hot summer temperatures and the tree's shallow root system demand more careful and frequent watering than may be required in other areas.

Timely irrigation is essential for proper citrus tree growth, development and fruiting. Never allow the root system to dry out completely as trees may become stunted, have reduced yields or die from drought stress.

For newly planted trees, remember that the most critical irrigation period is from the year's initial growth flush until the young fruit are at least one inch in diameter.

If you are growing lemons, kumquats or limes in outdoor pots and water runs from the bottom of your pots quickly, the soil may have dried out so much that the water is running down the sides of the pot instead of reaching the roots. Break up the surface of the soil and gently water until it is saturated.

Moisture monitors can be helpful in checking the hydration of your soil and are available at local garden centers.

Lemons, oranges and other dwarf citrus in outdoor containers need to be

watered deeply at least once or twice a week. If you are growing fragrant evergreen citrus inside your home, water with one-quarter to one-half gallon every five to seven days.

Successful fruit production also requires an adequate supply of essential nutrients. Since citrus has different nutrient needs at different stages of its growth and fruiting, be sure to buy fertilizer especially formulated for citrus, and follow the label directions carefully.

Some citrus are easier to grow in our area than others.

'Improved Meyer' lemons are a valley favorite. Meyer lemons are thought to be a hybrid between a lemon and a sweet orange or mandarin. They are very juicy and have less acid than other lemons. Meyers lemons will often produce the first year, need no pruning other than optional shaping and even make an excellent hedge. 'Improved Meyer' is more cold hardy than a true lemon, although it will still need a sheltered spot and protection from frost. Best of all, a Meyer lemon can show blossoms and mature fruit at the same time, producing abundant lemons for the kitchen and delicious fragrance throughout much of the year.

Kumquats are an intriguing, less common fruit that marries a kitchen treat to a beautiful landscaping option. They do well for some Napa County gardeners. For those who have not tried them, kumquats are oval to round citrus fruits that look like miniature oranges. The whole fruit is edible. The rinds are spongy and sweet, while the pulp is tangy and sour.

Dwarf kumquat trees grow three to six feet tall. Standard trees are about twice that size and are very ornamental and symmetrically shaped with dark green leaves, richly perfumed white blossoms and showy orange fruit. Kumquats require high heat to bloom and set fruit, so are well suited to our Napa Valley summers.