Days are much longer now than they were during January and February and house plants need to be watered more often, especially those getting good light.

About 50 per cent of the water taken up by the roots passes out through leaf pores as water vapor. The process is called transpiation. Unless the roots can replace the water lost through transpiration, the plant wilts. Continued wilting cancause death.

Transpiration occurs mainly when there is light. During dark hours, leaf pores close, limiting water loss. When light is restored, they open.

The rate oftranspiration depends on factors such as temperature, relative humidity and light intensity. With warmth, low humidity and good light, transpiraion will be relatively heavy.

A good system to follow is to feel the soil every day and when it starts to feel dry, water the plant. Using room temperature water, apply until it comes out through drainage holes at the bottom. Wait about 15 minutes for excess water to drain and empty the saucer. Don't let the pot stand in water very long.

Spring is one of the best times to repot house plants if they need repoting plants that make a lot of growth usually need repotting once a year or even more often. Foliage plants such as philodendron and rubber plant can be kept in the same pot two or three years. Check the roots. If they are visible and matted, a change to the next size larger is desirable.

If too large a pot is used, a lot of the soil is not occupied by roots, it stays wet too long and increases the risk of root rot, one of the most serious diseases of house plants.

Recently purchased house plants should not need repotting for several months.

Many people put their house plants outdoors for the summer. In most cases it may not be a good idea, according to Dr. Charles A. Conover, director, University of Florida Agricultural Experiment Station, Apopka, which devotes itshelf almost exclusively to the problems of foliage house plants.

Indoors the plants probably receive rather low light to which they have become adjusted. If placed in full sun foreven a short time, they will suffer cell death from high temperatures.

Plants accustomed to full sun have what are called sun leaves which are smaller than shade leaves of the same species and thicker in the cross section. When placed indoors under low light they are unable to photosynthesize the food needed because they are very inefficient under low light. This results in the plant consuming stored food. If the food lasts long enough for the plant to adjust to the different environment, which may require three months or longer, the plant can survive: otherwise, it dies. Shade leaves are able to make maximum use of light energy.

If there is a shady place under a tree, the plants can spend the summer outside without being sunburned. It is best to wait a full month after the last killing frost before leaving them out overnight.Some can be damaged severely if the temperature drops even into the 40s.

The plants will grow more vigorously outdoors and require more water and fertilizer than they would indoors. Hanging baskets particularly are prone to water stress. A diluted liquid fertilizer applied every two weeks can provide the necessary nutrients. Follow directions on the label.