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Greenhouse plants in pots, flats, or benches are completely dependent on the grower for their needs. Watering is perhaps the most important and demanding job of all. Establishing a good greenhouse watering schedule is important.

Most plants are largely made up of water. A growing plant gives off tremendous quantities of moisture (in the form of vapor) through its leaves; this is called transpiration. If water is not available in the soil so the plant’s roots can replace this transpiration, the plant will wilt and quite possibly die.

With potted plants there is a simple and generally reliable way to tell when water is needed. Rap the pot with the metal part of the hose. A dull thud means the soil is moist, a sharp click that it is dry. Or you can be guided by the feel of the top-soil. If it is still slightly moist to the touch, the plant does not need watering.

Plants growing in the unheated or cool greenhouse do not need as much water as those in a warm greenhouse. You will find, too, that plants in small pots dry out faster than those in large pots. As has been said, "There is nothing ’thirstier’ than a healthy plant growing in a 2-inch pot, especially in summer." The last three words rate re-emphasis, for in sunny, summer weather plants use water rapidly and the soil in the pots may become so dry you have to water twice a day or more.

Cyclamens and gardenias require frequent watering. They grow fastest when their soil is always slightly moist. Cacti and geraniums, on the other hand, do not need much water, although geraniums need more than is commonly supposed. Plants affected by a disease usually need less water than healthy specimens.

Remember this: It’s always better to under-water than to over-water. You want your plants to mature as quickly as possible so you can turn them into cash but they must be at their best. Keeping them too wet does not promote stocky growth.

Many growers still prefer the tried and true watering method; that is, fill the pot up to the top with water and let it seep through the soil. For this to be practical (and require just one filling) there must be at least % inch of space at the top, more in large pots. Do not let plants stand long in water. Watering thoroughly at intervals is better than a slight moistening each day, which only reaches the upper soil and roots.

Of course, vigorously growing plants need more water than dormant or slow-growing ones. Water oftenest during hot summer weather and in winter when the sun is bright. Give less water during cloudy spells or when humidity is high. For example: Through one summer which was unusually hot, but with very high humidity, I found that plants in flats in my greenhouse required watering only twice a week; potted plants needed it only every other day.

However, in hot but dry weather the plants in flats needed water at least three or four times a week, the potted ones every day, and often twice a day. If possible, water plants in the morning, so the sun can evaporate the water during the day. Wet foliage at night is prone to mildew or fungus troubles.

Syringing plants with a strong stream of water will remove dust and wash off red spider mites, but do not expose plants to direct sunlight until they have dried off. Sun shining on wet foliage causes burned spots, particularly on hairy-leaved plants like African violets and gloxinias.

Make sure that you establish a greenhouse watering schedule that works best for your plants.