Gardening : Two Avocado Trees That Produce Superb Fruit : Fruit: The new Gwen is especially good for small gardens, while the Reed has been around for years.

Two little-known, but marvelous avocado trees for Southland yards, the Gwen and the Reed, have one thing in common: They produce fruit of superb flavor and quality.

The trees are quite different. The Gwen is small and well-suited to small yards, while the Reed, although slender, may grow up to 35 feet and requires at least a medium-sized yard.

The size and shape of the fruit from the two trees is also quite different. The Gwen produces fruit about the size and shape of the typical Hass avocado, while the Reed produces huge, rounded fruit weighing more than a pound.

Both varieties are not yet popular in the area, but a good choice for Southern Californians.

The Gwen, with its small size, is more practical for most Southern California yards. A fairly recent introduction, it was developed by Berthold O. Bergh of UC Riverside. Although not yet well known, those who have planted it rave about it.

The tree is only about one-third of the size of a typical avocado tree, yet it produces huge quantities of fruit that have a magnificent rich, nutty flavor.

Most people consider the Hass (the leading commercial variety) to be the flavor standard from which other avocados are judged. The Gwen produces fruit whose flavor equals or exceeds that of the Hass--perhaps because the Gwen is a grandchild of the Hass.

The fruit resembles that of the Hass, with its thick, pebbly skin, but unlike the Hass, the skin does not turn black when it ripens.

The Gwen tree naturally grows to about 15 feet in height, but it can be kept even smaller because the tree has small limbs and is easy to prune.

Production is another attribute of the Gwen, it produces huge clusters of fruit. Its total production is usually superior to other avocado varieties whose trees are much larger. The Gwen bears fruit over a long period, usually from April through September.

Since the Gwen avocado is fairly new, the trees can be difficult to locate.

Four nurseries usually stock the Gwen trees: Palos Verdes Begonia Farm in Torrance, (213) 378-2228; Atkins Nursery in Fallbrook, (619) 728-1610; C.P. Teague Nursery in Corona, (714) 735-2300, and Pacific Tree Farms in Chula Vista (619) 422-2400.

A nursery can also order one from a wholesale grower such as La Verne Nursery in San Dimas.

While the Gwen is new, the Reed has been around a long time. Indeed, there are some magnificent old specimens in Riverside yards. The tall, slim trees are excellent producers of softball-size fruit with an incredibly rich, buttery flavor. It is probably the richest flavored avocado in existence.

Reeds take a longer time to bear than Gwen, but once established, the trees are reliable producers. The harvest period for Reed generally runs from July to September.

Reed trees can also be difficult to locate; try the sources for Gwen trees listed above.

Both Gwen and Reed are fairly frost-sensitive. Check with your local nursery about the climatic conditions in your particular area. If you live in the colder sections of the Southland’s inland valleys, you should select a more frost-tolerant avocado variety.

An avocado tree needs a sunny planting site that drains well. If allowed to stand in water, the tree will not survive. It should be kept moist, but never soggy. Older, mature trees will get along on a less frequent watering schedule than young trees. However, every fourth or fifth irrigation should be a deep one to wash away accumulated salt in the soil.

In most Southern California soils the avocado tree will thrive with very little fertilizer. A light application of an avocado fertilizer containing chelated iron in the spring on a yearly basis will suffice. Always water thoroughly after fertilizing.

The avocado tree requires very little pruning, other than for shape and size.

The fruit of the avocado is harvested when it is full-sized and mature, but still hard. Green-skinned varieties such as the Gwen and Reed are usually picked when the fruit loses its shine.

A few more tips in harvesting avocados, don’t pull them from the tree by the stem, but use clippers and cut them off as close to the fruit as possible.

Also, never leave the harvested fruit out in the sun because it sunburns easily. Allow the fruit to ripen at room temperature; this usually takes about a week.

Sidnam has written garden columns and features for The Times since 1975.