Think of it as free fertilizer.

That's the beauty of a compost pile. Instead of throwing out your yard waste, you can transform it into a potent, soil-enriching pulp right in your own backyard.

Gardening gurus love it, and for good reason. It's the ultimate in citizen recycling.

Compost not only helps keep an estimated 30 percent of your rubbish from going into a landfill, but it helps break down Hawai'i's heavy, clay soil. Plants will look and grow better, said Robert Speer, a master gardener at the Urban Garden Center in Pearl City.

"It's going to be a fertilizer that has nitrogen in it that will enhance the growth of your plants," he said.

Speer, a 60-year-old retired Navy captain, converted two 50-gallon plastic pots — the kind used for planting trees — to create compost at his Mililani home. Because organic material decomposes faster if you move it around, Speer will regularly empty one pot into the other to "turn" his material.

"It's just right for a fairly large yard," he said of his system. "I put my tree clippings and so forth, and grass clippings, in there."

Turning your pile of material is called "hot composting." While it requires regular maintenance — weekly turning and enough water all the time to keep it moist — this method generates compost in about four weeks.

"The hot method is faster and preferred," Speer said. "It's a better way because it bakes the seeds and kills any weeds and pathogens. If done right, the temperature can get up to anywhere from 120 to 160 degrees. The hotter it is, the faster it decomposes."

The alternative is "cold composting," and it's a simple pile of unattended yard waste that can take up to six months to become compost, Speer said.

2 KINDS OF MATERIALS

The success of your compost pile depends on the ingredients. All materials are either carbon- or nitrogen-based, and you'll need a working balance between the two — one-third green, or nitrogen-based, and two-thirds brown, which is carbon-based, Speer said.

Green ingredients include grass trimmings and food scraps. Brown ingredients include twigs, chopped up branches, dried leaves, peels, sawdust and egg shells.

Be sure to cover the fresh nitrogen-rich material with carbon-rich material, which will produce a fresh smell.

Vegetables, fruits, peels, coffee grounds, egg shells and leftover rice all make good compost, but don't use meat, bones, or fish scraps, which can attract too many bugs and animals as well as maggots.

There is seldom an odor associated with your decomposing waste, but it helps to cover the container, and in the case of kitchen scraps, bury them under a layer of grass clippings, Speer said.

But even then, it will probably attract a few bugs.

"If you get a lot of food scraps in there, you have a tendency to draw some of the less desirable bugs, in particular cockroaches," Speer said. "You may find it less desirable to have around, but the resulting compost is excellent."