Fall leaves. Beautiful, but what do you do with all of them?

Compost them, silly.

Spokane Master Composters will be on hand Saturday at the Fall Compost Fair at the Finch Arboretum to teach people about ecologically composting their yard waste. And while the adults are learning about composting, the kiddies can play in a big pile of leaves at the Fall Leaf Festival going on at the same time.

Spokane County residents with proof of residency can also get a free plastic compost bin after completing a few educational activities.

The composting event is organized by the Spokane Regional Solid Waste System, which has offered two composting fairs a year for the past 12 years.

“We’ve done it as a waste-reduction effort,” said Ann Murphy, the group’s education coordinator.

In the beginning organizers handed out 400 to 500 bins at each event, but that number dwindled to about 200 per compost fair until last spring when it surged back up to 400, Murphy said.

“People have just gotten really intent on practicing these go green methods,” she said.

Murphy said she’s uncertain how much green waste is removed from the waste stream through composting or clean green bins, but said it makes a significant impact.

Murphy said that people should keep in mind that leaves alone don’t a compost pile make.

Though leaves will very slowly compost over time if piled up by themselves, “hot” compost, which biodegrades more quickly, requires a mix of leaves and other materials.

Leaves are high in carbon, while green refuse like grass clippings, dying tomato plants and kitchen scraps are high in nitrogen.

Murphy said the optimum mix of materials for a hot compost pile is two parts green materials to one part leaves.

Of course, people can store leaves to be added to grass clippings and such next summer.

Other composting information will be available at the fair, where master composters will demonstrate techniques and show off a worm bin.