The Campbell Reporter

Gardening

Tart Fruit: The kumquat is a thornless tree popular in home gardens, and it produces the familiar oblong kumquat fruit. The rind is sweeter than the tart fruit within.

There's a sucker born every minute on citrus understock

By Tony Tomeo

A 3-pound kumquat gets various reactions. Some people think that they have a very special tree. Some think that they have a very special garden. Some think that their fertilizer is very, very, very effective. Most are rather disappointed to learn that the fruit is actually not a kumquat at all, but a shattuck.

Almost all citrus are grafted. The upper part of the tree that produces the desired fruit is known as the scion. The lower part of the tree that provides roots is known as the understock. Most citrus that are popular in home gardens are grafted onto dwarfing understock, such as trifoliate orange, and most commonly, shattuck. Standard citrus trees (large trees grown for orchard production) are grafted onto standard understock, such as sour orange. Scions can be lemons (but are reputed to be quite reliable automobiles), oranges, grapefruits, limes or any desired citrus.

The understock sometimes produces suckers, or stem growth from below the graft. The suckers can overwhelm scions of slower-growing types of citrus, like kumquats and mandarins. When fruit eventually develops, it is that of the understock instead of the desired scion. More vigorous types of citrus can compete with their own suckers, so that both types of fruit are produced by single trees. Unfortunately, shattuck suckers produce useless bulky fruit on thorny, rigid stems. Shattuck thorns can be 3 inches long!

Understock can actually grow into trees from the roots of citrus trees that have been removed. Since removal typically involves cutting the main trunk near the ground and below the graft, the original type of citrus cannot regenerate new growth. This is sometimes a problem after a citrus tree is damaged by frost, cut down, but then later begins to produce new growth from the stump that is assumed to be the same as the original tree.

Older gardens sometimes have trees of standard rootstock. These can be even more confusing than dwarfing rootstock trees since most are the Seville sour orange, which resembles the more familiar Valencia orange. Regardless of how healthy they are, their fruit is good only for orange marmalade.

Only a few types of citrus are grown by cuttings, ungrafted and on their own roots. The Meyer or Richter lemon and the Seville sour orange, which is actually grown for marmalade, have no understock, so can not get suckers. Growth that develops from their roots will be genetically identical to the original tree. Meyer lemon trees can therefore regenerate from roots left after an original tree gets killed by frost. Seville sour orange can certainly do the same, but is likely to develop structural problems since it is a larger tree.

Incidentally, sour oranges are acidic like lemons. Sweet oranges are the familiar fruit known simply as oranges and that are presumed to be sweet. There are also sweet limes that are related to sour limes, but are eaten like sweet oranges. The Rangpur lime is actually a sour mandarin that is related to sweet mandarins. As if this is not confusing enough, Meyer lemon is actually a hybrid of a sour lemon and a sweet orange!

The difference between mandarins and tangerines is similar to that of champagne and sparkling wine. California sparkling wine is not classified as champagne because it is not from the Champagne region of France, although ironically, both are made from grapes developed in California. Tangerines were derived from Asian mandarins, but developed in the Americas, primarily Florida.

Fruit of the Week: Kumquat

Kumquats are considered to be and classified as citrus, but are actually of the separate genus, Fortunella. Nagami is a thornless tree that is the most popular for home gardens, and produces the familiar oblong kumquat fruit that sometimes can be found in markets. Meiwa is nearly thornless, with sweeter and juicier round fruit with fewer seeds, but is not as commonly available. Other kumquats are rare. Dwarf trees grow slowly to only about 5 or 6 feet tall. Standard trees grow slightly faster to only about twice as tall. The small orange fruit can be eaten whole. The rind is sweeter than the tart fruit within.

Listen to Tony Tomeo's 'New Image Garden Report' Friday mornings at 8:10 a.m. on KSCO-1080 AM (or online at www.ksco. com). He can be reached at www.ttomeo@ newimagelandscape.com or 408.358.2574.