Chris Kline, age 10, of San Diego, California, for her question:

 What exactly is peat moss?

Peat is a soggy mixture of boggy soil and partly decayed vegetation. In some parts of the world, people dig it up and let it dry in the sun. The dry chunks are used in fireplaces instead of coal. If a peat bog is left alone for a few hundred million years, it gradually turns into a bed of shiny black coal. But while a peat bog is still moist, it grows a wealth of assorted plants. And most of the plants that thrive in its soggy boggy soil are mosses.

Most of these different mosses are called peat mosses, just because they grow in peat bogs. The most common type is a feathery, greyish plant called sphagnum moss. This spongy peat moss can hold a lot of water plus pockets of air among its ferny greenery. This is one reason that gardeners use it. They mix it with soil to keep air and moisture around the roots of plants and also spread it around as a mulch. In time, this peat moss decays and adds rich plant food to the garden soil.