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Healthy citrus trees require year-round care

August 6, 2016
Wendy Irving

Since it’s August, we’ll start here. This is the time of year to fertilize for the last time. Citrus needs nitrogen, phosphorus, potassium and possibly micro-nutrients such as zinc or iron.

Ask your local nursery for a recommendation on a fertilizer formulated for citrus and apply according to instructions. You should be irrigating newly planted citrus twice a week and more frequently during dry spells and watering established citrus deeply once a week, enough to keep the soil moist.

If your citrus tree is in a container, water when the soil is dry 1 to 2 inches down; if in the ground, when dry 4 to 6 inches down. Make sure you still have a layer of mulch around the tree, away from the trunk, to help keep the shallow roots cool and to reduce moisture loss. Be consistent with your watering schedule (best to use a drip system), and watch out for overwatering.

If you have lemon and lime trees, you may have fruit ready to harvest, since varieties of these types can produce year-round.

In September, continue to irrigate through hot days until the weather cools, then reduce irrigation frequency. Do not apply nitrogen (which promotes growth) after August as tender new leaves may be damaged by an early frost. Check for ripening fruit of early varieties. Remember, unlike other fruits, citrus does not continue to ripen and get sweeter after it is picked. Ripe fruit will generally be fully colored and easy to remove from the tree, but taste-testing is the best judge.

In October, continue checking for ripeness. Decrease watering.

In November, December and January, have fun harvesting. To maintain a healthy, productive tree, remove fruit as it matures. Decrease watering to once a month if needed. Watch for frost forecasts and make sure your tree is well watered if temperatures sink.

On a frosty night, cover your trees to protect them with canopies made of wood stakes and canvas (not plastic), or string outdoor lights in the branches. If we do have a significant freeze, remove and use any damaged fruit. The longer damaged fruit remains on the tree, the greater chance of decreasing later fruit yields. However, do not prune damaged branches during these months.

In February, it is time to start fertilizing again just prior to bloom. You will want to continue fertilizing every four to six weeks through August. Start to watch for insect eggs and spray with an appropriate biological insecticide (Neem oil), if necessary.

Mid to late March is a good time to plant new trees. Pick a sunny and warm spot that has good, well-draining soil. The most important timing factor on planting a new tree is to give the tree’s roots the longest possible time to get established before they are subjected to environmental stresses. That can vary with the climate in your area.

On established trees, resist the urge to prune any frost damage until the danger of frost has passed and before the start of a new growth cycle. Pruning citrus is not for fruit production, but rather shape, size and structure, the basics of which are usually accomplished in the first three years.

Beyond that, pruning is done to remove dead, diseased and damaged portions of the tree and any suckers below the graft. If you do prune, the ideal time is just prior to bloom or just after fruit set so that the tree can adjust its fruit load during the June drop. Minor pruning can be done at any time, but avoid late-season pruning, which can stimulate excessive tender growth that is likely to be injured by frost.

Compost, mulch and monitor watering conditions. And watch for signs of aphids, citrus leaf miner and scale, again using an appropriate biological insecticide (Neem oil or spinosad), if necessary.

In April, increase watering, continue to monitor for insects, and refresh mulch.

In May, June and July, continue to fertilize, and get on a regular deep watering regimen of at least once a week. Maintain mulch. In hot areas, paint bark exposed to direct sunlight with a half/half solution of water and water-based interior latex white paint to prevent sunburn. Continue to monitor for insects, making sure of their true identity before you treat. Beneficial insects are out and about now and will help keep balance in your garden.

So we have come full circle. If you would like more information on solving citrus pest problems with minimal risks to people and the environment, please visit the University of California Integrated Pest Management website at ipm.ucdavis.edu and search “citrus.”

For more in-depth information on other aspects of citrus care, go to homeorchard.ucanr.edu and click on “fruit/nuts” and search for “citrus.”

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