Roger's Tree Pick: citrus family

‘Citrus’ is the common name for the genus of plants in the Rutaceae family, which hails from Asia’s tropical and subtropical regions.

These aromatic, evergreen-like large shrubs and small trees produce highly fragranced fruit with leathery rinds and juicy, pulpy interiors that are a wonderful natural source of vitamin C.

As a landscape plant, they offer year-round attractive form and glossy deep green foliage, fragrant flowers and decorative fruits in season.

If you want quality fruit, your choice of varieties will depend on the total amount of heat available throughout the fruit-developing period (need varies according to the type).

• Heat requirements: Lemons and limes need the least heat and will produce usable fruit in cool-summer areas and where winter temperatures are not too low. Valencia oranges have a higher heat requirement and greater frost tolerance. Navel oranges need even more heat. And with blood oranges the saying is “the more heat, the more sweet.”

• Hardiness: Citrus of one kind or another are grown in Arizona and California where winter temperatures do not fall much below 20 degrees F. From least hardy to hardiest, citrus generally rank in this order: Mexican lime (28 degrees), limequat, grapefruit, pummelo, regular lemon, tangelo and tangor, Bears lime, sweet orange, most mandarin oranges (tangerines), Improved Meyer lemon, Owari mandarin, sour orange, orangequat, kumquat, calamondin.

• Standard or dwarf: Practically all citrus sold have been budded or grafted on an understock. Standard tree (20 to 30 feet tall and as wide) are grown on a variety of understocks. Dwarf trees are grown on understocks of trifoliate orange which produce trees four to 10 feet tall (some may eventually reach 15 to 20 feet). Check citrus periodically for suckers (branches that arise below the graft line) and remove them before they compete with (or overwhelm) the desired variety.

• Drainage: First requirement is fast drainage for most citrus. If soil drains slowly, don’t attempt to plant citrus in it regardless of how you condition the soil.

• Watering: Citrus needs moist soil – but never freestanding water – and they need air spaces within the soil particles. Danger from overwatering is greatest in clay soil, where air spaces are minute. Water established trees every other week and don’t let the tree reach a wilting point. Citrus roots extend out twice as far as the distance from the trunk to the branch ends or the so-called “drip-line.” Use tensiometers to take the guessing out of when to water.

• Mulching: All citrus benefit from a two- to three-inch layer of good clean organic mulch. Citrus roots grow fairly near the surface and the mulch also keeps the root-zone cool, aids in retaining water and cuts down on weeds.

• Fertilization: Citrus in general are fairly heavy feeders and will respond to a good cross section of NPK (nitrogen-phosphorus and potassium). A feeding in late winter, once in June and again in August will assist in their nutritional needs. Citrus may suffer from iron chlorosis or zinc deficiency, which can be treated with chelated iron or iron sulfate. Commercial products containing both iron chelates and zinc are available as sprays directly to the foliage.

• Pests and diseases: Citrus trees can be plagued by aphids, snails, slugs, mites, scale insects and mealybugs. I like to give citrus plants an occasional spraying of jets of water to upset the various bugs; this also cleans the dust from the leaves which some bugs like to hang out in. Consider the many natural and organic ways to treat these pests so that you have wholesome, clean fruit to eat.

• Sunburn: Citrus bark sunburns in hot-sun areas. Don’t over-prune citrus trees and open them up too much. Commercial citrus growers allow the trees to carry branches right to the ground when production is heaviest on lower branches.

• Citrus in containers: Try using the genetic dwarf forms of citrus in large containers. I have a kumquat tree outside my studio in a large terra-cotta container and for four months in the winter I enjoy a handful of these small tasty fruits a day, eating the outside rind and all. The art of espalier can be applied to the citrus family on a wall or fence. And now more growers are producing espaliered plants with grapefruit, kumquat lemon, lime, mandarin, orange, tangelo pomegranate and even a variety of avocado called Holiday.

In our next visit we will explore the many citrus varieties that can be grown in San Diego County, including some types you might not of have heard of, so that you can become more sustainable in growing and enjoying the harvest from your own gardens.

Roger Boddaert is a landscape designer/Certified Arborist. He can be contacted at (760) 728-4297 for consultations and designs.

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