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Robert Smaus

A Seasoned Gardener Learns New Tricks to Grow Citrus

June 04, 1988|Robert Smaus

June has always been the traditional citrus planting month in Southern California--or so I thought. But according to Mary Lu Arpaia, a UC Riverside Extension subtropical horticulturist, it's a little on the late side.

"April and May are best, but June is better than September," she said.

The idea is to get citrus in the ground after the last possible frost but before the hot weather. Planting in the spring gives them plenty of time to become comfortable in their new surroundings before coping with the chilly winter weather. (Young plants with tender new growth are the most susceptible to frost.)

I had always heard that June was a good time because citrus needed warm soil, but it turns out that they don't like heat at planting time. But this was only the first adage to fall under the ax.

Citrus trees do most of their growing in spring, and that is the best time to fertilize, even though this is not the time often recommended. Arpaia suggests fertilizing in late February or early March, when new growth is just beginning, and then again after the trees have flowered, late in spring. She says not to fertilize while the trees are in bloom.

As an alternative, fertilize a little each month but do not fertilize navel oranges or winter-fruiting mandarin oranges with any fertilizer high in nitrogen after July, because it may affect the December-to-January crop.

Another adage says citrus, like most trees, need infrequent but thorough watering--"soak it once a month" is what I've heard. But research has shown that most citrus roots are in the top 18 to 24 inches of soil, which is relatively shallow. Citrus need more than monthly irrigations.

Water Needs Vary Greatly

Precisely how to water is difficult to spell out because it varies so much depending on soil and climate, but with roots so shallow it is easy to check. Dig a little hole and see if the soil is moist a few inches down. It should be at all times--moist, but not wet. Should you err on the side of too little water, you can soak the tree and it will probably rebound if you then keep it moist.

Citrus are pretty tough trees, Arpaia says. Too much water is more likely to be fatal, bringing on root diseases. Sickly, yellowish leaves are often a sign of too much water.

Leaves with veins that remain green but that turn yellowish in between are chlorotic, which means they are missing one or more trace elements. Trees are more likely to be chlorotic in alkaline soils, but this can be cured by fertilizing with chelated iron and other trace elements, available at all nurseries.

Mikeal Roose, assistant professor of genetics at UC Riverside, put the ax to another citrus myth--that there are "true dwarf citrus."

"There are no true dwarf scion varieties, as there are with peaches or other fruits." Don Durling of Durling Nursery in Fallbrook put me on to Roose because Durling is trying to get the dwarf question straightened out so people are not misled by nursery tags and labels.

Citrus labeled dwarf are really semi-dwarf. All citrus are made smaller by grafting them onto rootstocks that slow the plant's growth. They are not naturally dwarf. If you were to take a cutting and root it and then plant it, you would get a full-size tree.

The roots most commonly used are Rubidoux trifoliate, which reduce the size of oranges, tangelos and Dancy tangerines by about 45% and grapefruit and Satsuma mandarins by about 70%. On this rootstock, citrus can be expected to grow to 9 to 14 feet in about 10 years.

Smaller in Containers

To keep the trees even smaller, you must grow them in containers or prune yearly. These are the trees that should be labeled semi-dwarf, and they produce excellent fruit in a wide variety of soils and climates.

Those citrus that should be labeled dwarf are grafted onto a rootstock called Flying Dragon. These will only grow 6 to 8 feet in 10 years, but there are some catches.

First, the process of growing the rootstocks is tricky, and not all will make dwarf plants. And then it is an expensive operation because the plant grows so slowly. At a nursery, customers are likely to think they're getting gypped, because they have to pay so much for such a small tree. As a result, these dwarf citrus are not easy to find.

Also, there is a tendency for citrus budded onto Flying Dragon to become chlorotic in alkaline soils where the pH is above 7.0. They also need to be watered more often, because they have a smaller root system and do not do as well in sandy soil or where water has much salinity. But they have proved to be fairly cold-tolerant and are resistant to many citrus diseases.

So, should you decide to plant citrus now (which is better than in September), expect to find trees at nurseries that are semi-dwarf, no matter what the label says, unless it clearly says Flying Dragon, or unless the nurseryman can assure you that is what it is budded on. Otherwise, expect a tree to grow to 10 feet or more and allow enough room. Or, plant it in a pot. Citrus are one of the better choices for containers.

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