Garden Detective

Garden Detective: Why aren’t her oranges sweet?

Oranges should be allowed to ripen on the tree.
Oranges should be allowed to ripen on the tree. Bigstock

We have a 7-year-old Washington orange tree in the southwest corner of our yard. It has a lot of fruit every year. I feed it citrus stakes at the right time of the year. The fruit doesn’t turn orange until late February, and is thick skinned and NOT sweet. Is there any hope for this tree? We also have a young lime bush that hasn’t produced fruit and a lemon bush that I transplanted from a patio pot to the ground. It also has not produced fruit. This neighborhood used to be an orchard; all our neighbors have sweet producing orange trees. Is it the variety?

Dona Ryan, Carmichael

Most likely, you’re picking too early. According to UC master gardener Carol Rogala, the harvest season for sweet oranges varies based on the cultivar. Early season oranges are harvested October to January, mid-season oranges are harvested December to February and late-season cultivars are harvested March to June. In the Sacramento area, Washington navel oranges are harvested from January through April in home gardens.

Your fruit might look ripe, but may not be. You can’t tell the ripeness of an orange by its color. Citrus should be allowed to ripen on the tree. Essentially, citrus are fully ripe when they have reached the color, size and flavor as specified for their type. Pick fruit when mature – and before the hot weather.

As for your lime and lemon trees, citrus trees usually grow little during the first year after they are planted. If they receive enough water and fertilizer, they grow substantially during the spring and summer between their second and fourth years. During this time, they may occasionally flower and yield fruit. From the fifth year onward, citrus trees enter their fruit-bearing stage. When they begin bearing fruit, they grow more slowly, especially during the winter. They reach their full size 10 to 14 years after planting. After 20 to 25 years, the trees reach their peak production and their yield of fruit declines.

There are some things you can do to increase the yield and the health of your citrus trees. Besides providing the basics of maximum sunlight, protection from winds and planting in well-drained soil, focus on giving your plants proper nutrients.

As for fertilization, many home gardeners don’t fertilize their citrus at all, or use compost/mulch around their trees and get quality fruit. Bear in mind that excessive fertilizer can run off into the 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 (with 15 to 20 feet 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 fertilizer bag, using a decimal for both. For example, if you need to apply one-quarter pound of actual nitrogen, and you are using ammonium sulfate, which is 21 percent nitrogen, the formula would be .25 divided by .21 equals approximately 1.2 pounds of fertilizer.

Because adequate levels of nitrogen are required during flowering and fruit setting, late winter or early spring broadcast 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 re-greening of Valencia oranges. On the other hand, lemons give a beneficial yield response to moderate nitrogen during the summer.


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