Garden Detective

Garden detective: Orange tree may need more time

About six years ago, I planted a 24-inch-tall Valencia orange tree in my backyard (purchased from Capital Nursery), with a dream of picking oranges in a few years. The tree appears healthy, and has grown to more than 6 feet tall. But, alas, no oranges. Not even any flowers. I live in the Pocket area, and have good soil and strong sun. Should I wait longer? Pull it out, buy another one, and plant in another location? I planted it near the location of an old walnut tree I removed. Is there a walnut tree issue here?

–Steve Gevercer, Sacramento

Citrus trees often take 10 years or more before they bear fruit, so wait a little longer. Your Valencia should start bearing fruit soon.

Walnut trees can cause toxicity problems for a wide range of other plants – notably apples and blueberries – but usually citrus can cope OK. Because your orange tree has grown and appears healthy, the walnut apparently had no effect.

Instead, keep your tree happy and healthy while it matures. Here are some pointers from UC master gardeners:

Citrus need moist (not soggy) soil, and benefit most from deep infrequent irrigation, but over-watering is not good. Drainage is very important. Checking your soil for drainage is a must.

Does it hold the water too long or drain quickly? Try testing the drainage by digging a small hole and examine the soil in the rooting zone to about 1 foot deep.

Soil lightens in color when it is dry. Feel the soil (this is especially important during times of drought). The soil should hold its shape when squeezed or rolled into a ball when wet. If it does not, it’s too dry.

These same guidelines apply if your tree is in a container. It’s important to determine the amount of water it needs. Mulch can help keep the soil moisture even and consistent (but don’t let it mound around the trunk).

Citrus trees can benefit from feeding in late winter or early spring. The boost in nutrients can help spur flowering and fruit set. If you choose to fertilize, the following is recommended:

A fully bearing, average-size mature orange, lemon and grapefruit tree – 15 to 20 feet foliage diameter – planted in the ground, should be fertilized at a rate of about 1 pound of actual nitrogen per tree per year. This same formula applies to mandarins, limes, kumquats and other common citrus. (A tree your size would need about 1/4 to 1/3 pound of nitrogen.)

To determine how many pounds of fertilizer to 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 1/4 pound of actual nitrogen, and you are using ammonium sulfate that is 21 percent nitrogen, divide .25 by .21, which equals approximately 1.2 pounds. To get 1 pound of nitrogen, you need 4.8 pounds of ammonium sulfate.

For help in measuring, a 14-ounce soup can holds about 1.2 pounds of ammonium sulfate – including that quarter pound of nitrogen.

Because adequate levels of nitrogen are required during flowering and fruit setting, late winter or early spring fertilizer applications – broadcast over 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 re-greening of Valencia oranges.

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

Remember: Give your tree a deep watering right before applying the fertilizer. If you apply fertilizer without watering, it can burn the foliage.