QUESTION: My lawn is a type called soya grass. It's the first one in the neighborhood to turn yellow in the fall and the last one to turn green in the spring. Is there a simple way to fix this?

ANSWER: Though the mighty soybean can do many things, it cannot grow turf. You almost surely have zoysia, a grass often marketed as a "miracle" because it resists most of the ills that lawn grasses are heir to, including drought weeds and root-chewing insects.

Unfortunately, however, although zoysia is nearly unkillable, it is a warm-season grass, and that means it will be green only when the weather is mild. In areas where frost comes early and lingers long, cool-season grasses like fescues are a better choice.

Replacing the lawn may not be simple, but it is your only path to verdure.

QUESTION: The water- and pebble-filled trays under my houseplants invariably fill with green scum. Is there a way to inhibit this nuisance?ANSWER: Light on stale water equals algae. Light on stale water plus fertilizer equals algae bulked up on fast food. Start fresh by washing the tray and the pebbles with hot soapy water. Rinse well. After that, change the water weekly.You can buy a little extra time by adding a tablespoon of peroxide to each quart of pebble water. But don't depend exclusively on better living through chemistry: Cleanliness is next to scumlessness.QUESTION: The garden that came with our house presented us with huge irises and lilies, all of which toppled over the moment they flowered. Should I set the bulbs deeper?ANSWER: There are many reasons for floppy stems. Some plants are simply that way by nature. Others have been bred to have such large flowers their stems cannot hold them up.Too much fertilizer can lead to stems that are tall but weak. Too little light can have the same effect. And rainy weather is often the clincher. Anything that tends to flop will do so when constantly damp.In any case, replanting will not help. First-year lilies might topple if the bulbs were not deep enough, but that yours are well established proves they are fine where they are. And iris are shallow-rooted plants.If things do not improve next year, either enjoy the lounging flower look or support the plants. Many find forked branches less obtrusive than the devices sold at garden stores.Address questions to Garden Q& A, The New York Times, 229 W. 43rd St., New York, NY 10036, or by e-mail to gardening@nytimes.com. Those of general interest will be published.