Thursday, December 18, 2014

Garden Doctor: Reducing olive production, caring for citrus

Pomegranates are tasty fruits that grow on deciduous broad plants up to 15 to 20 feet tall. Fruit-bearing plants come in a number of varieties and offer choices for specific California locations. Courtesy photo

From page A6 | January 08, 2012 |

Question: What growth bears the fruit on olive trees? Do they need fertilizer? When do you prune olive trees? Is there anything you can spray on the tree so it doesn’t produce so much fruit?

Answer: Olive trees (Olea europaea L.) have been cultivated since before recorded history. They grow best in a Mediterranean climate such as ours.

Fruit is produced on one-year-old shoots with plentiful sunlight. One method to cut down on fruit production is to allow your tree to be bushier. You will still have fruit on the outside, but the quantity should be greatly reduced. (However, a tree that is too dense is prone to pests such as the black scale insect.)

Olives generally do not need fertilizer, especially where fruiting is not the goal. They can grow in shallow soils of only 3 to 4 feet deep and even when planted in the deep, rich soils, the roots still will remain shallow. Approximately 70 percent of their roots grow in the top two feet of soil. The roots extend laterally, far outside the canopy of the tree with a few main roots digging vertically.

Prune an olive tree in the spring or summer when there is little chance of rain. If you prune during the bloom and/or when there is early fruit development, this too will help manage your crop quantity for you can actually prune out some of the one-year growth.

There are a number of sprays on the market for reducing fruit production, and you can research them by doing an Internet search. They are expensive and, in general, require careful timing to apply while the tree is in flower bud to full bloom, not stressed and the weather is right. Be sure to use the correct concentration. No spray is 100 percent effective; all sprays add chemicals into the environment so use judiciously if you choose this path.

Question: How much watering and fertilizing do citrus trees need? I have two lemon trees; one is doing very well and another planted nearby is struggling, although they seem to have the same exposure and same soil.

Answer: You have the makings of a natural experiment, and if you make some careful observations you may be able to answer your own question. By the way, your question is the right one. The major strategies for successful citrus are regular fertilizer and consistent watering, but not overwatering.

Once trees are established, the soil should partially dry out between waterings. You might consider building up a water trough with soil around each tree at its drip line, and watering there. This will avoid soaking the trunk, which can lead to diseases. Or you could use a drip system or micro sprinklers.

For more information, download the Garden Note “Growing Citrus in Sacramento” at, or request a copy by calling the Yolo Master Gardener office at the number below.

Question: My neighbor asked me about pomegranates — do you prune them or simply let them be a bushy tree? What growth produces the fruit? Are there any pests to pomegranates?

Pomegranates grow naturally as deciduous, rounded, multi-trunk, broad plants 15 to 20 feet tall. They can be kept to a smaller, 10-foot version and are often seen as a small tree or shrub. Prune pomegranates in the late dormant season as fruit is borne only at the tips of new growth, it is recommended that for the first three years the branches be judiciously shortened annually to encourage the maximum number of new shoots on all sides, prevent straggly development and achieve a strong, well-framed plant. After the third year, only suckers and dead branches are removed.

Fruit-bearing plants come in a number of varieties and offer choices for specific California locations. Plants that fail to fruit or bear fruit that is more decorative than tasty make good landscape plants with taller varieties used as foundation plants, as tall hedges or small trees.

Lower-growing plants are excellent for edgings and in containers. Pomegranate fruit may be kept refrigerated for up to seven months.

Pomegranates are resistant to oak root fungus and are not attacked by codling moth or twig borers. The major insect pests for pomegranates are omnivorous leaf rollers, cotton aphids and ash whiteflies. They are sensitive to frost in fall and spring and do not mature well in cool climates. The plant tolerates a wide variety of soils and even grows well in our alkaline soil. They will tolerate drought conditions but prefer regular watering and full sun.

For those looking to learn more about gardening, several classes will be offered this month:

* Master Gardener classes at Woodland Community College — “Dormant Pruning of Deciduous Fruit Trees” from 9:30 to 10:30 a.m. Saturday, Jan. 14, at WCC, 2300 E. Gibson Road, Woodland; and

* Master Gardener Classes at Central Park Garden — “Dormant Pruning” from 9:30 to 10:30 a.m. and “Care and Pruning of Roses” from 11 a.m. to noon, both on Saturday, Jan. 21, in the Central Park Garden at Third and B Streets.

— Send questions, addressed to the “Garden Doctor,” by email to, voicemail to (530) 666-8737, or regular mail to UCCE Master Gardeners, 70 Cottonwood St., Woodland, CA 95695. Be sure to include your contact information because any questions not answered in the Garden Doctor column will be answered with a phone call or email to you. You can request the Yolo Gardener newsletter delivered by email and learn more about the Master Gardener program in Yolo County at



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