I have an orange tree that has produced a good crop every year, and last season was the best. But this season, the tree had very few blossoms and I have a hard time counting the number of oranges on the tree because they are so few.

Why? The tree doesn't have signs of disease or bugs, and it's only 20 years old. It gets plenty of water, sun and appropriate shade.

I live in West Sacramento and the soil is healthy. Are others writing in about the same thing?

– Art Shumaker, West Sacramento

According to UC Master Gardener Veronica Simpson, weather affects the growing season in many ways. That may have been the case with your tree.

As for fertilization, many home gardeners don't fertilize their citrus at all and still get quality fruit. Bear in mind that excessive fertilizer can run off into gutters and pollute creeks and rivers.

If you choose to fertilize, the following is recommended:

A fully bearing, average-sized mature orange, lemon or grapefruit tree (15- to 20-foot foliage diameter) should be fertilized at a rate of about 1 pound of actual nitrogen per tree per year.

To determine how many pounds of fertilizer to actually use, divide the desired amount of actual nitrogen by the percentage of nitrogen on the bag, using a decimal for both. For example, if you need to apply a quarter-pound of actual nitrogen and you are using ammonium sulfate which is 21 percent nitrogen, the formula would be .25 divided by .21, which equals approximately 1.2 pounds.

For help in measuring, a 14-ounce soup can of ammonium sulfate has about 1 pound of actual nitrogen.

Because adequate levels of nitrogen are required during flowering and fruit setting, late winter or early spring broadcast of fertilizer applications to the soil can provide the required nitrogen supply.

Some references recommend dividing the nitrogen fertilizer into thirds (early spring, summer and fall), but UC Cooperative Extension specialists point out that high levels of nitrogen fertilizer are to be avoided for oranges and grapefruit during the summer and fall, as that contributes to thicker rind, lower juice content and regreening of Valencia oranges.

On the other hand, lemons give a beneficial yield response to moderate nitrogen during the summer.

Avoid fertilizing during hot summer months. Scatter the fertilizer over the root area under the tree and 1 to 2 feet outside the drip line. Water the fertilizer into the soil. In addition, keep weeds and mulch away from the trunk, allowing for air, light and water exposure.

Proper irrigation is also very important. Give regular deep soakings of the entire root area.

Pruning of long upright shoots and strong laterals helps strengthen shoots and prevents crowding in the tree center. That will help production, too.

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:

• Sacramento: (916) 875-6913; 9 a.m.-noon and 1-4 p.m. weekdays

• Amador: (209) 223-6838; 10 a.m.-noon Monday through Thursday; email ceamador.ucdavis.edu

• Butte: (530) 538-7201; 8 a.m.-noon and 1-5 p.m. weekdays

• El Dorado: (530) 621-5512; 9 a.m.-noon weekdays

• Placer: (530) 889-7388; 9 a.m.-noon on Tuesdays, Wednesday and Thursdays or leave a message and calls will be returned

• Nevada: (530) 273-0919; 9 a.m.-noon Tuesdays through Thursday or leave a message

• Shasta, Tehama, Trinity: (530) 225-4605

• Solano: (707) 784-1322; leave a message and calls will be returned

• Sutter, Yuba: (530) 822-7515; 9 a.m.-noon Mondays and Tuesdays and 1-4 p.m. Thursdays

• Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returned

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