It's the season to compost.

If you would consider composting and, in turn, creating invaluable humus to grow better plants, then begin now while nature is providing the materials for free. With leaves falling, a golden opportunity presents itself: Instead of discarding the leaves as you have done for years, compost them over the fall and winter. Nature will do the rest, generating its best soil for you to use as you please in the spring garden. Once you begin composting, you will never again trash leaves.

There are many avenues to composting, so you may want to explore your options. Do remember, however, that shredding leaves, grass clippings and other organic matter will accelerate the composting cycle dramatically. An inexpensive, electrically-powered shredder costing about $100 is your best choice if you are composting for the first time. Here are several ways to compost:

Composting bins. City gardeners should opt for this economical tool (less than $100) which accepts up to six cubic feet of leaves, clippings and such. Fabricated of heavy-duty, heat-absorbing plastic, these bins come in assorted sizes. Most practical are the small, portable bins that can be located in full sun, but are accessible from the rear door of the house. If you shred leaves, you should be able to process most garden leaves in the one bin. The owner's manual provides complete instructions on composting and secondary materials that are needed.

Composting barrels. These are 55-gallon drums on stanchions that allow for self-enclosed composting, but on a large scale. A retractable cover makes it easy to add materials to the drum while a hand-crank on the side allows the barrel to the turned; older drums were difficult to turn, but improved gearing on recent barrels has made turning much easier.

Bins. Whether you create them from cinder block or concrete block, wood or screens, these bins are the best vehicle for suburban and rural gardeners. No matter what material you use, allow for oxygen movement into the bin. Blocks should be placed on their side to permit oxygen to enter the pile.

Windrows. You can compost directly on the site where the humus will be used to grow flowers or vegetables next spring. This includes compost piles erected for raised vegetable gardens; here, you could temporarily place cinder blocks to outline the raised bed, compost within the borders, then remove the blocks next spring when the cycle is over and humus has been created.

Whether you compost in barrels, bins or windrows, here is the sequence of events:

With bins or windrows, don't skimp on size. Bins should be at least seven to eight feet long, five to six feet wide. Windrows should be no more than four feet wide, eight to 10 feet long, to facilitate a raised bed for flowers or vegetables. You can border the area with sod that is spaded from the garden and overturned.

If composting on the ground, place layer of small twigs, branches and such over the soil to allow oxygen to move into the base of the pile through the early part of winter. Remember that anerobic bacteria (mesophyllic) involved in the initial decaying process require oxygen, therefore allowance should be made for air to enter the pile at all times. Aerobic bacteria (thermophyllic), which complete the composting sequence at temperatures of 110 to 150 degrees, do not require oxygen.

Tree leaves are next. If you merely scatter leaves over the twigs, put down a four-inch layer of leaves; if you shred the leaves, a five-inch layer is good. Use all tree leaves with the exception of leaves harvested from fruit trees; dispose of these leaves.

A heat source is next, preferably inorganic 5-10-5 fertilizer. Fill a 12-ounce coffee can with the granules, then scatter them over a 150-square-foot pile (a 10-by-15-foot compost heap).

If you have a source of fresh cow manure, use it now. You can apply shovels of the manure liberally over the pile or combine with 0-20-0 superphosphate to chelate phosphorus in the soil. Premix the manure in a wheelbarrow. To three heaping shovels of fresh cow manure, add a heaping shovel of 0-20-0, then homogenize your materials before strewing the final product over the compost pile.

Lime is next, sprinkling two shovels of ground limestone or pulverized dolomitic lime for every 75 square feet of the pile.

Soil. Apply an inch of good-quality soil to top off this first layer of the compost pile. Avoid using clay soil as it merely pollutes the quality of the final humus. Instead, use peat humus, Michigan peat or leafmold to add soil support.

At this point, wet everything down with the garden hose, perhaps a gallon of water uniformly applied over the layer, then proceed to create a second layer of the same materials. Ideally, a five-foot-high pile is your goal, assuming you create windrows or used enclosed bins.

Bacteria is now added to the pile. While the cow manure is teaming with bacteria, you may not have access to the fresh manure in the first place, in which case you rely on a "compost activator."

A number of activators are available, containing aerobic bacteria, fungi, enzymes, actinomycetes, algae and yeasts. Activators (some brand names are Bio-Dynamic, Compostar and Compost Maker) accelerate the decay process and improve the quality of humus. Follow the label instructions, mixing with water first in the house and allowing the mixture to stand in average room temperature for a full day prior to use.

Lacking an activator, use granular kitchen yeast instead, allowing it to stand in a quart of warm water for 24 hours, adding two gallons of water to the solution. No matter which product you use, scatter it over the pile after you have put down all your layers, not as you create the pile.

A week later, use a "compost fork" (about $20) to turn over the entire pile, but leave the twigs in place at the bottom. Immediately after, soak the pile with five to 10 gallons of water. Turn the pile every week up through the middle of December. At that time, you will turn the pile, soak it again, then cover with a sheet of black plastic drawn tightly in place to retain heat and moisture. The pile will heat for the winter, yielding humus when the black plastic is removed in late March.

Apart from launching a compost pile now, other priorities will keep you busy this weekend. For example, it's poinsettia time.

If you are caring for a poinsettia from last Christmas, don't change your care schedule. However, if you grew new poinsettias this year from cuttings taken from the mother plant, you need to adopt a new care program this weekend.

Starting today, the poinsettia should stay in a warm room with bright indirect light for nine consecutive hours, then is moved to an unused room where total darkness can be assured for 15 hours. However, the air temperature is critical; it should be in the 62- to 66-degree range for best results. Consider locating the plant in a closet in a vacant room during this cycle. The next morning, return the poinsettia to the sunny room once more. This schedule should remain in effect for the next five to six weeks, after which the daily darkening phase is discontinued.

All the while, keep the soil lightly moist, but not soggy; if you used 1-1-1 as your soil formula, you shouldn't experience drainage problems of any kind. Because nitrogen must be in the cell tissue at all times, you should plan on wetting the soil with Peters's 20-20-20 plant food instead of warm water. Constant feeding with Peters will assure optimum plant performance.

Then there is the holiday cactus. If you want flowers on the plant for Christmas, you need to get the plant's biological clock going this weekend or first thing next week. Contrary to what you may have been told, you don't darken the holiday cactus to make the flowers occur; you chill the plant.

In the next few days, chill your Thanksgiving or Christmas cactus for two or three consecutive nights. Move the plant to the floor of an enclosed garage in the evening, returning the plant to the house the next morning.

During the day, the plant should be in the warmest possible room with bright indirect sunlight. If your plant is now in a cool room, move it to the warm room immediately so the plant gets a "fix" on warm temperatures. As long as the nighttime temperature is about 20 degrees lower than the daytime temperature, the plant's clock will start running.

If you don't have an enclosed garage, move the cactus to the trunk of the car overnight. In every case, remember to move the plant indoors first thing next morning.

Jack Eden is the host of "Over the Garden Fence" Sundays from 10 a.m. to 1 p.m. on WTOP Radio (1500 AM).