|Standard Cyclopedia of Horticulture|
Watering. The watering of plants usually exhibits the skill, or the lack of it, of the gardener. It is a practice that cannot be well explained in print, although a few general statements may be made.
An abundant and convenient supply of pure fresh water should always be a first consideration in locating a garden or greenhouse. Having this, the next matter is knowing how to use it, for here, good gardeners say, lies nine-tenths of the elements of success. Certain it is, especially in the indoor cultivation of plants, that more depends on knowing when to give or withhold water than on any other single matter. The art of watering is unteachable; it requires experience, judgment, skill. Some knowledge of the commoner facts of vegetable physiology, physics, and soil physics will be helpful, but even then experience will be necessary.
In American gardens watering is usually performed with a hose from a stored water-supply. Two common types of watering-cans are shown in Fig. 3998.
A fairly safe guide to watering is: never water plants until the soil has become dry, though not "powder-dry," and then give them a thorough soaking. Plants dislike a continuously wet soil. In the care of plants in earthenware vessels, a useful test is to thump the jar. If it rings the soil is dry; if the sound produced is dull the soil is sufficiently moist. Such rules, however, are only for the novice. They presuppose activity of growth, and take into account only one consideration aside from this, and that is the condition of the soil as regards moisture. The experienced gardener reads his practice in his plants and the conditions under which they are being kept. The following suggestions are based on the most important considerations.
Actively growing plants may be watered very freely, as a rule, whereas in a dormant or semi-dormant state the same plants will require only occasional waterings. Soft-stemmed or rapid-growing plants ("soft-wood" and "herb-like" plants), and those with large leaves, need, as a rule, an abundance of water when growing actively. Hard-wood or slower-growing plants, with smaller leaves, must be watered with greater care. Soft-wooded plants, with some exceptions, may at times even flag somewhat for want of water, and recover without permanent injury when a fresh supply is given. Hard-wooded plants, as camellias, azaleas, and heaths, on the other hand, suffer permanent injury from becoming too dry. It is safest to allow no plant in active growth to flag.
The amount of foliage affects the plant's capacity for using water. Plants which have been cut back, or which from disease, insects, or other causes, have lost most of their foliage, must be kept drier until they have regained their foliage. Unhealthy plants are benefited, as a rule, by being kept rather dry until they begin to show signs of renewed vigor.
Small cuttings, or any plants freshly potted or newly transplanted, are not in condition to use much water until the root-hairs have attached themselves to the soil-particles and growth has begun. A thorough watering at the time of potting or repotting the plants, especially if they are subsequently shaded for a few days, is usually sufficient until they have become established.
The character and bulk of soil should be kept in mind. Porous and warm soils dry out much sooner, while the heavier clay soils are in danger of becoming water-logged and sour unless watered with care. When there is a large mass of soil in proportion to root- development, as in the case of greenhouse beds newly set with young plants, care must be used in watering until the soil is occupied with roots.
Serious trouble often begins in the greenhouse from a heavy watering at the beginning of a period of dark muggy weather. Not only does such watering do damage to the soil and roots, but the excessive humidity of the air about the plants and its weakening effect on their tissues invite the attacks of various mildews, fungi, and insect pests.
The time of day is important. In the greenhouse in winter free ventilation is usually impossible. At night there is a tendency toward a damp atmosphere. Careful florists, therefore, water in the early part of the day at this season, so that the house will have become somewhat dried out by nightfall. It is seldom advisable to let plants under glass go into the night with wet foliage. It gives the fungi a chance. Especially hazardous is it to water cutting benches or boxes of young seedlings late in the day in the winter season. The various damping-off fungi find under such treatment the condition suitable for their development. Excessive humidity on the interior of a closed plant-house is most likely to occur in moderate weather. During severe weather the condensation upon the glass is large and renders the air of the house drier. During summer, when there is free ventilation, the watering may advantageously be done late in the day. Midday watering at seasons when the sunshine is very bright is often followed by scalding of the foliage unless the plants are well shaded. Ferns, Rex begonias, Chinese primroses and richardias are among plants easily injured in this way.
Consider the temperature at which the plants are kept, the position of the heating-pipes, the amount of light, and the freedom of ventilation permissible in watering plants in glasshouses. It is better, as a rule, to have the watering conform to these conditions; but frequently the practice must be reversed.
The temperature of the water exerts a marked effect on the growth, flowering, and fruiting of plants. It is now held that, in general, the water should be of a temperature close to that of the air in the house where the plants are growing, or about 10° F. below.
Watering may be indirect. Shading the glass of greenhouses in summer with some suitable material is much practised by florists for the purpose of sheltering plants from too great intensity of light, and for the purpose of reducing evaporation and transpiration. Certain kinds of plants, as palms, and some kinds of ferns, require this; also newly potted plants. Syringing of walks, by reducing the temperature and increasing the humidity of the air, also tends to reduce transpiration and save watering. Watchfulness and attention to ventilation are necessary, however, to avoid excessive humidity, which tends toward a soft watery growth and extreme sensitiveness and susceptibility to disease.
Vessels to contain plants should always be provided with openings at the bottom for perfect drainage. This, in a measure, is a safeguard against overwatering. Investigation has shown that a soil which is kept continuously wet through bad drainage or otherwise is rapidly impoverished through loss of nitrogen. A fermentation is also set up in the roots, which, through the formation of various deleterious products, results in their destruction.
While a constantly wet soil is always very objectionable, thoroughness in watering as often as the plants need water is of the greatest importance. When enough water has been supplied there will be more or less dripping from the bottom of the pot. It is a good plan to leave a space of 1 1/2 to 2 inches or more at the top of the pot, according to its size, for the reception of water. This space should be so large that when filled the supply of water in soaking downward will penetrate to the bottom of the vessel.
Plunging the pots or tubs is a means of controlling the water-supply. The late William Scott gives the following advice on this practice: While it is true that most of the water given to the plant passes through the soil and escapes from the hole in the bottom of the pot, yet much that is left in the soil—which is considerable if the soil is saturated as it should be—is evaporated from the porous sides of the earthenware pots. In warm sunny weather, plants in small pots, standing on a bench, dry out very quickly. This can be avoided by plunging the pots in some material, as coal-ashes, tan-bark, or, better than all, spent hops. When plunged to the rims, only half of the surface-watering is needed, and the advantage of less watering is shown by a marked improvement in the health and vigor of the plants. Such a benefit is this plunging that plants which would otherwise need a shift into a size larger pot can be carried along another month in perfect health. This applies more particularly to quick-growing soft-wooded plants, geraniums more especially, for these are quickly exhausted by too frequent waterings.
In watering beds in the open ground and lawns, the chief consideration is thoroughness. Superficial waterings induce the formation of roots near the surface. Neglect and subsequent drought then prove more disastrous than ever. The evening is the best time for surface sprinkling. Watered in the heat of the day, grass and various other plants are likely to have the foliage injured. Ordinarily it is better to avoid watering beds of plants in the open ground if possible or delay it until really necessary, and then water thoroughly. Other references to watering may be found in the article "Greenhouse Management," beginning on page 1408, Vol. III; see also "Sub-irrigation in the Greenhouse,” page 1684.
Pests and diseases
- Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963