The thought of getting their fingernails dirty in the garden disenchants some plant people at this time of year.

Already, they have exchanged outdoor activities for the television to watch as much weekend football as possible. For those people, with the exception of occasionally mowing of the lawn, the 1990 garden is history.

Fortunately, not everyone feels that way. Even with the formal end of summer early tomorrow when the autumnal equinox occurs, many homeowners have come to realize that fall has nearly as many virtues and rewards as spring, especially in the garden.

They know that the last two weeks of September is hardly the time to put away the shovels and working clothes. Instead, r it is a time to pick up mislaid plans.

This weekend and next, go back to the drawing board to see where your landscape plans went awry: Where were you supposed to plant azaleas, but never did? You had your heart set on a flowering lilac, but never followed your dream. You lost trees to borers, but isn't it time you conquered this nemesis?

Picture what you always wanted your landscape to be, then spend the next two weeks making it happen.

Some aspects of fall planting are never achieved, so let us touch on the major ones.

First, price. In most garden shops, the price of nursery stock hasn't increased since spring despite rising maintenance costs in the past four months. Price usually reflects work. For example, plants were watered daily for the past 16 to 20 weeks, and sprayed routinely for disease and insects. Plants in your garden probably received considerably less care than those at the nursery.

Second, growth and plant vitality. Flowering plants are nearing the end of a complicated two-month period during which the dormant buds for next spring's flowers have been produced and set.

This applies to plants from flowering almond and dogwood to Bradford pear, quince and rhododendron. Evergreens, shade trees and foliage plants received no less attention during this time to achieve optimum growth. Careful inspection of fir, pine and spruce will reveal the second season of growth now underway.

Third, timing. Properly planted over the next two weeks, shrubs and trees will survive the winter well in your garden.

Periodic watering is all that is needed, but no fertilizer at this time of year. A spray of Forever Green or Wilt-Pruf to woody branches and limbs as well as limbs and needles of evergreens in early November is the finishing touch.

Lastly, aesthetics. Hundreds of azaleas flowering at the nursery mean nothing when they should be decorating gardens of Washington area homes. Why buy azaleas in flower next April at the nursery when you really want them flowering in your own garden then?

The excuse about "not knowing flower color" is no longer valid because most azaleas come with tags showing blossom color and detailed planting instructions. All you need do is plant properly, then let nature do the rest.

Before shopping, put some environmental issues on paper.

Where do you intend to plant: full sun or partial shade? How much room is there? Does the soil drain water well or is there standing water after a thunderstorm? Only a few plants, such as red twig dogwood or swamp maple, will prosper in soil that is wet most of the time.

Are you landscaping to solve a problem, such as neighborhood pets on the lawn or vehicle noise on a busy street, or are you building a barrier to provide privacy? Don't shrug off these problems because each one has a horticultural answer.

If your situation recently has changed, are you now landscaping for minimum maintenance? Are you looking for plants without disease and insect problems that need only random attention?

Jot down these and other environmental conditions, make a quick sketch of your existing garden, head for the garden shop and turn your problems over to the manager.

If you go on a weekday, most managers will be able to resolve your problems and make recommendations on the spot. If your needs are basic, the manager probably will suggest specific plants that meet your environmental needs. In most cases, shrubs and plants come with the nursery's guarantee, so check accordingly.

As for planting, things are not the way they were five, 10 or 15 years ago. The scenario has changed, so you may want to make copies of the accompanying sketch for reference as you plant shrubs and trees.

If you're not able to plant yourself, most garden shops and nurseries have a trained crew that will do the job at a cost, of course.

If you plant, nursery stock will come balled-and-burlapped or in containers. The planting procedure differs in each case.

With container plants, withhold water when you bring them home so the soil dries thoroughly; then a few raps with the fist at the base of the pot will remove the plant in one piece. Check the rootball and you will find roots wrapped around the outer wall of soil.

Use a tool with a hooked end, such as a crochet hook, to take hold of the hairy roots and pull them gently from the ball of earth. Pull the roots randomly away from the ball. When you're through, the plant should have the frizzy-hair look. Leave the container plant intact while you prepare the balled-and-burlap plant for planting.

Such plants should be allowed to go on the dry side for a day before planting, so withhold water accordingly. Before planting, cut the cord holding the rootball to the trunk, then carefully roll down the burlap on all sides so most of the rootball is exposed. Do not remove the burlap altogether. If the soil is dry, the soil will stay in place.

Now, measure your plants so you know what size hole you need. The hole should be 1 1/2 times as deep as the height of the rootball or container. The width should be 1 1/2 to 2 times the width of the rootball or container. Refer to the illustration above to familiarize yourself with the hole configuration.

If you have clay soil, discard everything taken up from the hole. With sandy soil, you will return some of it to the hole after planting.

In clay soil, place a two- or three-inch layer of sharp sand at the base, then backfill with a 50-50 mix of the same sharp sand together with good quality compost, leafmold, Michigan peat or peat humus. Mix this thoroughly before working it over the sandy bottom. Water the hole to settle materials, then add more of the 50-50 mix as needed.

Container and balled-and-burlap plants are planted two-thirds in the soil, one-third above the soil line. Exceptions are azalea, camellia, holly, juniper, laurel, pieris japonica and rhododendron, which are set half in the soil, half above the soil line.

Work the 50-50 mix on both sides of the plant, creating a wave of soil from its crest to where it meets the ground some 12 inches away on all sides of the plant. Water to remove air pockets and to settle the wave of soil, then add more soil as needed. Finally, mulch with a three- or four-inch layer of pine bark nuggets.

In sandy soil, lay down a 5-to-1 mix of organic materials to the very sand removed from the hole. Organic candidates include leafmold, compost, peat humus and Michigan peat.

To help retain moisture in the soil, add one or two teaspoons of an acrylic copolymer -- such as Grosoke or Water Grabber -- to the mixture. Fill to the proper height to accommodate the plant, adding water to settle things. Add more soil around the plant and above as shown in the sketch.

Sprinkle water at this point to remove air pockets, then create your wave going away on all sides of the raised knoll. Then mulch with pine bark nuggets.

A couple of final tips:

Don't fertilize any nursery stock planted this fall. Come spring, you can rake the mulch aside, work two shovels of organic materials into the top few inches, then return the mulch in place. Regular applications of fertilizer won't begin until late October 1991 for trees and spring 1992 for shrubs.

Pace yourself, even if your landscaping efforts are spread out over a week or two. Water the plants every day up to the last 24 hours before planting, so the soil is dry when you get your fingernails dirty. Jack Eden is the host of "Over the Garden Fence" Sundays from 10 to 1 p.m. on WTOP Radio (1500 AM).