A plant for a three-year-old? Don't be too quick to say no

As a mother who's raised several preschoolers, I know what a challenge it can be to teach young children to be responsible for the items they use. I usually counted it a fortunate day when toys were picked up and laundry flung into hampers with a minimum of maternal nagging and fuss.

So when our three-year-old daughter wanted a houseplant of her own, I responded with a resounding ''No!'' Just the thought of some poor little vine withering from neglect was enough to make me feel guilty.

She continued to beg, however, and I found myself considering the idea again. If she could learn to care for a plant in a responsible manner, it might carry over into clean rooms and organized toys, too.

We visited the plant section of a nearby discount store, and after steering her away from the more exotic varieties, I allowed her to choose an English ivy. Proudly, she carried it home. She chose a cracked saucer to place underneath the small pot and set it on the low windowsill of her bedroom.

''Hello, Ivy,'' she chirped happily. ''This is my room, and these are my toys , and. . . .'' Well, horticulture books do suggest talking to growing things. Our daughter was off to a good start.

Since she had begun to decipher the meaning of a calendar, I hung one near her bed, X-ing in each Wednesday and Saturday as ''watering days.'' Using a discarded cream pitcher as a watering can (just the right size for small fingers), I showed her how much water to add. From that point, she and the ivy were on their own.

Surprisingly, the plant flourished. It was not too demanding and willingly overlooked sporadic droughts when the young gardener forgot to check her calendar. Since it was hardy, it also endured an occasional hug, kiss, or spill. It wasn't long before the preschooler's loving care was rewarded by a healthy vine.

Since that time, our daughter has added to her collection. Her room now holds a blooming begonia, a philodendron, and two small cactuses (which require a special watering schedule, since they like a dry soil).

I am still responsible for pruning and occasional feeding. My daughter, however, takes her watering duties quite seriously and enjoys moving plants to different corners of her room. She introduces them to her playmates, has learned the names of several species, and last spring even started a flat of marigolds on the windowsill. Only three survived to be transplanted into the yard, but the look of wonder on her face as the yellow flowers finally bloomed was worth every moment of the tending.

Interested preschoolers are capable of maintaining a small plant collection, if a few rules are observed:

1. Start with one plant, set in an easy-to-reach place. (Make sure that crawling babies or pets can't get at it.) Let your child know what is required - and then stand aside and let her, or him, do it.

2. Choose hardy and fast-growing varieties; they survive mistakes and stimulate the child's senses. (''Can you see another bud forming?'' ''Can you feel that this plant's leaves are smooth and the other one is rough?'' ''Does this flower have a smell?'')

3. Should a plant die, treat the matter lightly. Buy another ivy, go over the instructions again, and let your preschooler know you have confidence in him, or her.

4. Encourage your child to share the hobby with playmates and adult visitors. Small children need and deserve attention and respect, and showing a collection they alone have grown and nurtured is a sure way to build self-esteem.

Tending plants can help a preschooler learn about kindness, gentleness, and ''cause and effect.'' It can prepare children for the day when they will care for their own puppy or kitten. Best of all, it gives them a bit of control over their own environment, the chance to feel responsible and wise and very capable - though they may not have gotten around to picking up their toys.