Marin Master Gardeners
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Citrus ideal for California gardens

December 12, 2014
Anne-Marie Walker

What says sunshine more than a bowl of citrus on a kitchen counter?

Citrus is notable for fragrance found in blossom, leaf and fruit. Each of us has experienced the sudden fragrant and intoxicating haze created as we peel an orange. This volatile, flammable oil is generally toxic to bacteria and insects and is a plant defense mechanism. Fortunately, over time, we have developed positive responses to citrus as do bees hungry for citrus nectar.

Native to Asia and a member of the Rutaceae family, citrus is ideally suited to the California garden. Evergreen, prolific and low maintenance, a citrus type can be matched to everyone's garden. The cultural requirements of citrus include:

• Six hours of sun, preferably south-facing exposure

• High summer heat to develop sugar

• Low winter temperatures to cause acid levels to drop — but avoiding freezing temperatures

• Temperatures between 70 and 90 degrees for steady growth

While it is possible in Marin to plant citrus year round, the best time to plant is in spring. This permits the shallow roots of citrus to establish before cold weather. Plant the root ball just a bit above grade and build a water basin wider than the spread of the leaves. Citrus are good candidates for 5-gallon or bigger containers. Water once a week during warm weather moistening the entire root area that can extend up to twice as far as the tree canopy. Mulch can help keep citrus moist but keep mulch away from the trunk collar.

Citrus are heavy feeders benefiting from regular monthly fertilizing. In general, harvest oranges from December through May, limes from August through March, mandarins from January through April and lemons year round. Remember you need not harvest the fruit all at once. Because citrus fruit contains little starch, a desired sugar-acid ratio should be reached before harvest. Taste is the best indicator of ripeness. Once picked, they will not sweeten whereas citrus left on the tree will get sweeter.

Citrus trees have relatively few pest and disease problems. The best defense is proper irrigation and fertilization. Common citrus pests include whiteflies, thrips, mites and rots. These bring black sooty mold on the rind of the fruit, which can just be washed off. Snails and slugs will eat flowers and fruit. Pick them off in the early morning. Aphids, scale, or spider mites may infest a tree. Control of ants helps ward off scale. If your tree suffers from scale, cut it out, pruning to allow sun into the interior of the tree. Keep a look out for a new invasive, the Asian citrus psyllid. It is a small brown insect about the size of an aphid and can jump or fly. It carries an exotic disease that causes irregular yellowing of leaves and inedible, bitter deformed fruit.

There is no cure.

Lastly, fruit quality can be impacted by several factors. Generally, citrus bloom in spring. Puffy fruit with a thick rind can occur with off-bloom fruit, set from a summer or fall blossom. Simply discard this fruit. Fruit splitting is caused by dry weather followed by a good rain. Proper irrigation practices best mitigate these problems.

A bountiful harvest of citrus allows you to juice, make jams and jellies, as well as candied rind. Peels can also be used to make flavorings, dried powder zests and libations including limoncello, an Italian lemon liqueur and vin d'orange, a sultry fortified wine made from Seville oranges, also known as marmalade oranges. More possibilities include citrus butter, citrus salsa, citrus curd and citrus cakes.

How lovely to share your garden's citrus bounty with friends and family during the holiday season.

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