Kathy Karns, age 13, of Roanoke, Illinois, for her question:

Can plants really grow without soil?

Nowadays, lots of people are growing healthy plants without soil. This amazing trick is called hydroponics—and “hydro” gives a hint as to how it is done. It means water, and reminds us that even though cer¬tain plants can be persuaded to get along with soil, their roots must have a plentiful supply of water. What’s more, the water must be a balanced food formula containing a special assortment of dissolved chemicals.

The tops of the plants are in the air, where they get the right amount of light. Their roots dangle down into a tank containing the solution of dissolved chemicals. They are propped upright with a layer of netting or by sandy gravel in the water. The liquid formula must contain a steady diet of calcium and magnesium, potassium and nitrogen, sulfur and phosphorous. Also, traces of certain minerals and many other chemicals must be provided—and some plants need more of this or that. The task is tricky, but plants can be grown hydroponically, without soil.