They're called "memory gardens" by some, nostalgia gardens by others, but the concept is the same. The garden is a family history.

There's a flowering cherry, now some 25 feet tall, planted when the oldest child entered high school. Out back, there's a blue spruce that was a gift from a grandparent, now deceased. The azaleas . . . they were an anniversary gift to both of you from the children many years ago. On and on it goes, every shrub and tree with a memory of its own. Unfortunately, the once-proud landscape is now an overgrown jungle, but who will dig the soil to change things?

Nothing is forever. When the hour comes to sell, prospective buyers won't share your values of the landscape. More likely, they will disdain the jungle of overgrown plants; and the landscape you thought to be a major selling point will become a liability. The garden no longer will be a bargaining chip. Chances are you'll have to drop your price.

Homeowners in these situations are sure to have torn emotions -- "What will the children say if we tear things down?" -- yet there are several options worth considering long before the axe falls on the memory garden.

First, consider moving the more valuable shrubs to gardens at the homes of children, grandchildren or relatives. Trees are too costly to transplant, but shrubs planted a generation ago can be moved effectively so as not to endanger their survival in a new garden. If you are of a mind to pursue this, try to transplant before Memorial Day or postpone the move until next March or April.

Second, if children are too far away to consider transplanting, homeowners should consider donating the plants to a church, school or nonprofit institution. The resultant tax deduction eases the pain.

Third, conversation with neighbors and friends usually will locate a source for your excess plants; in such cases, the recipient generally does all the digging, packing and such.

Finally, if all efforts fail, there are a host of companies that, for a price, will remove shrubs and trees and resell them on their own.

Depending on the location and size, old gardens are frequently an environmental headache for potential buyers. Overgrown shrubs crowd the front of the house to the point that they prevent any light from entering the rooms. A prospective buyer walks past the curtain of massive shrubs, enters the house and is enveloped in a wall of darkness; instead of sunlight cascading into the room and extending a bright welcome, the guest finds the only light source to be illuminated lamps on the tables. Depressing!

In such cases, "saving plants" is impractical and undesirable. Over the years, the shrubs have been pruned so many times that the vertical canes and stalks are thicker than handles on professional hammers; growth is so poor that the only choice is to dig them up, cut them into small pieces and add them to the trash can. Extend this thinking to plants around the entire house as you exchange tired, overgrown shrubs and dense shade for an open environment and welcome sunlight.

Once the old garden is gone, don't succumb to tradition. Disregard the neighbor's advice to get a new landscape going right away. Instead, enjoy the dividend of a leisure garden for 1986. Invest in sun-loving annuals where you simply couldn't grow them before. Pick up some tomato plants (or start your own from seed) and savor the taste of a vegetable you haven't grown in years. If you're adventurous, add a splash of color with perennials so you have carryover plants for next year. Don't worry about buying new shrubs, but enjoy a different garden for a change. Come next spring, you'll lay in a few shrubs, but only after you seek help from a trusty garden shop manager; over the winter, he'll provide lots of ideas worth exploring, including some dwarf shrubs that always will complement the house. Reams of material are available from the Cooperative Extension Service.

Finally, be a copycat. There are carbon-copy homes in your neighborhood built years ago, but they have young gardens created by young owners. Take pictures of these exteriors, then modify the garden to suit your needs.

Real estate brokers also can be a source of information. A good broker will share information about recent home sales in your area to give you a good picture of homes that are selling and those that are not. Compare the two and you may be able to draw some conclusions about your landscape program when the memory garden is terminated.

A few reminders for the weekend landscaper:

*The dogwood borer season has opened and will continue through the first days of July. If you whitewash the trunk (two cups of ground limestone to a quart of water, stirring and painting), the borer may not even pause at the dogwood. Painting the trunk from soil line to the first crotch with Thiodan (one-quarter teaspoon to 8 ounces of water) is a good defense. A final Thiodan painting about July 4 will end things nicely. For the moment, check the trunk for any holes (caulk these shut) or nicks in the bark from the rotary mower or weed-trimmer; caulk them, too.

*Birch trees will be attacked momentarily by the female birch leafminer. She lays eggs in the very center of the leaf tissue, after which the babies mine the leaves, causing them to drop in July. A second wave arrives in mid-July to finish what the first brood missed. Liquid Malathion at two teaspoons per gallon of water (only in the evening) is good for immediate control. Plan another application around July 20-25 for the summer brood.

*Fertilize spring-flowering shrubs if you have skipped this chore up to now. Use Hollytone for azaleas, but 5-10-5 for forsythia, lilac and pieris japonica. Afterwards, soak the shrubs.

*Shade trees are their fullest, and will now inventory carbohydrates for the balance of the growing season. The only exceptions to the rule are trees defoliated by gypsy moths; these will send out new leaves in mid-July to replace those lost to the moths. Gypsies have voracious appetites now in the final two weeks before pupating (resting) in early June. They will start mating about July 10-15, just about the hour the bare trees are sending out new leaves, but the moths won't be eating then.

*Don't overlook the newly planted bedding garden. Finger-pinch the side shoots routinely every week or so; if you smoke, wash hands thoroughly before touching plants.

*There is still time to plant shrubs and trees. Shop for the bargains, then catch next week's column for the ABCs of planting so you do it right.

Jack Eden hosts "Over the Garden Fence" Sunday from 10 a.m. to 1 p.m. on WTOP Radio (1500AM). Readers can write to him at 10621 Rock Run Drive, Potomac, Md. 20854.