Lack of water is the major threat to neglected plants. But you know how long your plants can go between waterings.So if your trip to Florida is for eight days and you’ve been watering your schefflera every five days, just give the plant a thorough soaking and then add a little extra water to its saucer. The plant will be fine.

If you’re skipping off for a one-month tour through Brazil, you‘d better do something more with your houseplants before you leave.

The key to plant survival, in this case, is either to supply water to the plants, to decrease their water needs, or a little of both.

KEEPING PLANTS SUPPLIED WITH WATER

This can test your ability to cajole friends, relatives or neighbors. But beware of entrusting plant care to those unfamiliar with your plants’ peculiarities; my cyclamen needs water every few days, while some of my succulents go all winter without a drop of water.

I use inexpensive automatic watering devices if my absence is to be longer than two weeks. A cotton rope, with one end buried in the soil and the other end dipped in a pan of water, will wick water to drying soil.

Another device, slightly more expensive but also more reliable, consists of a hollow, porous ceramic cone with one end of a long, flexible tube sealed into its lid. The cone and the tube are filled with water. They’re sold as “plant watering stakes” or “plant watering cones.” The cone is pushed into the soil, and the far end of the tube is immersed in a jar of water. Water lost from the soil is replenished by water drawn in from the reservoir.

Do not immerse plants in a deep container of water in an effort to provide them with an extended supply of water. Underwater the roots will suffocate and rot.

DECREASING WATER NEEDS

Plants have little holes in their leaves, called stomata, that let gases in for photosynthesis and let water out (transpiration). Moving a plant from a bright window to a dimly lit corner decreases photosynthesis, so stomata stay closed more often and transpiration decreases. Left too long without enough light, however, plants get starved for energy (which comes from photosynthesis), and leaves turn sickly and yellow.

Transpiration is how to keep plants cool. Lowering the air temperature will decrease plant transpiration and, hence, water use.

Yet another way to slow transpiration is to raise the humidity around your plants. I cluster plants together and fill their saucers with a shallow depth of water. For a longer vacation I drape clear plastic, such as a cut-open dry-cleaning bag, over the plants. Sticks poked into the soil keep the plastic off plants’ leaves. Clear plastic “umbrellas” are sold that do essentially the same thing in a neater way.

With a combination of diminished light, high humidity, automatic watering devices and perhaps the help of a friend, plants could fare well even after your monthlong vacation.

WORDS OF CAUTION

None of this advice applies to succulents, which include cactuses and other fleshy plants such as jade plants and sedums. These plants thrive on dry conditions, and rot if exposed to too much water, either in the air or at their roots. In this respect they are almost ideal houseplants. Go away on vacation and forget about them; tell your “plant sitter” that, too.