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8. Watering, Fertilizing, Shading, Pest Control

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. 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.

WATERING

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.

Equipment

For greenhouse watering, I use an all-purpose nozzle with a trigger control and a reversible cap. This is screwed onto the end of the hose. The nozzle provides an adjustable strong water stream or a sprinkle. With cap reversed it sends out a spray (fine or strong as you regulate it) which is good for cleansing foliage or applying liquid foliage fertilizers. With the cap re­moved, you get a full but fairly gentle flow to fill large pots or pails or for mixing quantities of fertilizer.

You can have automatic watering—either a homemade or a purchased system—but a small greenhouse operation may not justify it. One fairly simple method, actually semi-automatic because the water flow is controlled by hand, is sub-irrigation. A waterproof bench, (such as one with a metal liner), is partly filled with sand or gravel. The pots are placed on top of this layer. When needed, water (or liquid fertilizer) is piped into the bench via a permanent pipe connection or the hose until it reaches the base of the pots. When the soil in the pots has drawn up enough moisture through the drainage hole, the water is drained out of the bench.

If only a few pots or flats are involved, Fiberglas wicking, in contact with the soil in the pot and pulled through the bottom and into a pan of water, provides easy automatic watering. The important thing about sub-irrigating methods is that they as­sure consistent, even moisture to all plants.

FERTILIZING

Since you want plants to reach a salable stage in minimum time, you will have to pay considerable attention to fertilizing. A regular program is necessary. Decide on dates when you will fertilize plants, then try not to deviate from schedule un­less the weather upsets the expected rate of plant develop­ment.

Most growing plants need fertilizing at least twice a month. Liquid fertilizing is very popular. Some growers dilute fertilizer )i or % recommended strength and then give it at weekly in­tervals. Apply fertilizer to moist soil, for if the soil is dry, the chemical may burn feeder roots and cause a setback.

Types of Plant Food

There are many brands of organic and inorganic fertilizers on the market. If you prefer an organic type, I suggest fish emulsion, Ovene (a stick form of concentrated sheep manure), or liquid manure. You can prepare liquid manure by placing a half bushel of cow manure in a burlap bag and steeping it in a half tub of water for 2 to 3 weeks. Dilute this "brew" with water—to the color of weak tea—and then apply to your green­house plants. If you prefer the inorganic fertilizers, choose Ra-pid-gro, Hyponex, Plant Marvel, Spoonit, or something similar.

When plants are resting, they do not need fertilizer. Bulbs— amaryllis, haemanthus, other amaryllids, and tuberous or rhizomatous gesneriads—need no fertilizer and a minimum of water during their dormant period.

A complete commercial fertilizer includes proper proportions of the three main plant foods—nitrogen, phosphorus or phos­phoric acid, and potash or potassium (N, P, and K). Percent­ages are numbered on the container in that order. A favorite with many growers is 5-10-5. This means the fertilizer contains 5 per cent nitrogen, 10 per cent phosphorus, and 5 per cent potash.

Nitrogen helps plants produce heavy stems and good foliage. When soil is deficient in nitrogen, stems are short and weak and leaves turn a sickly greenish yellow.

Phosphorus aids plants in ripening tissues and seed. If you are planning for choice seed lots, include phosphorus (or super­phosphate, as it is usually sold in seed stores) in your fertilizer. Some gardeners add super phosphate, a layer a month, to the compost pile.

Potash is to plants what vitamins are to humans. Included in the plant diet, it aids in the formation and transference of starch. Potash helps plants grow huskier with sturdy stems and foliage, "fat" fruits, and strong roots. It is especially desir­able for root crops and such potted plants as gloxinias and amaryllis. If you use a 5-10-5 fertilizer, you can give your bulbous plants an additional weekly watering of muriate of potash, )i teaspoonful to a quart of water.

SHADING

Learning when and how to shade my plants was for me the most difficult phase of greenhouse operation. You can pur­chase various shading compounds (one called Garlands is pre­ferred by many growers). Cement, liquefied with a mixture of water and linseed oil and diluted until it is just thick enough to adhere to glass, seems to work best for me. I brush it on the glass with an old broom extended by a stick fastened to the handle. This shading holds for the summer, even through hard rains, and a small amount adheres during the winter.

By spring, when I give the greenhouse the annual housecleaning, the shad­ing has about disappeared and the glass is ready for another coat.

Another effective method is to use slatted shading which rolls up and down like porch shades. Layers of tobacco cloth fastened inside the house also are helpful.

Avoid linseed oil in any shading mixture intended for use on plastic houses. It is difficult to remove, as there is a chemical reaction between the plastic and the oil so that the shading "sinks in," becoming part of the plastic. Houses of polyethylene plastic can be shaded with layers of tobacco cloth or cheese­cloth fastened on the inside as well as by plastic screens inside or slat shading on the outside.

One orchid grower places strips of lath about 6 inches above the glass for both shading and cooling. Tinted shading may blend with the paint on your home but white shading is best, since it reflects more heat while allowing more light to pass through.

If you use cloth, it can be placed outside as well as inside for cooling and shading. In fact any type of shading used out­side, but with an air space between the shading and the glass, will help you operate your greenhouse more economically.

KEEPING YOUR PLANTS HEALTHY

Inthe small greenhouse the loss of a few plants means a decrease in profit. Proper ventilating, heating, watering, and fertilizing for the type of plants you grow are your best safe­guards against trouble. Sterilized soil is important, too. Plants growing in a cold or cool house are less susceptible to pest and disease than those in a warm house. Just remember the old say­ing about an ounce of prevention. Keep your greenhouse and the surrounding area free of weeds; they often harbor insects. The best way to fight trouble is to avoid it.

Products to Help You

Hundreds of insecticides and fungicides are on the market. Compare labels carefully. Then if you still are in doubt as to which product is best for eradicating an insect or a disease, con­sult your county agricultural extension agent. If there's any­thing he doesn't know, he can consult the state university. My own greenhouse medicine chest (which seems amply stocked for any emergency) contains the following items:

1. Sodium selenate in powder and capsule form for use against cyclamen mites. (This chemical is poisonous and some growers prefer a slower-acting though less poisonous insec­ticide, like Endrin.)
2. V-13  Nemacide,   a  preventative   and  annihilating  soil treatment for nematodes.
3. Malathion, a general all-round insecticide. (Lindane, is good for controlling insects invading the green parts of a plant; chlordane and DDT for eradicating soil-borne insects.)
4. Aramite (or Ovotran) for red spider.
5. Dithion for the brown scale on citrus plants, ivy, philodendron, and amaryllids. If you find a few scales on a plant or two, wash leaves in a strong soap-and-water solution. If you find scales on a number of plants, spray with Dithion or malathion.
6. Snarol for destroying slugs (or use Chlordane).
7. Fermate is my choice for a fungicide.
8. Carco-X, a combination fungicide and insecticide, I find especially good for treating soil for bulbous plants.
9. Sulphur as spray or dust is useful in controlling fungi or mildew.
   
   Most insecticides are poisonous. Handle them with care. Use rubber gloves when spraying the greenhouse. After you use the sprayer, rinse it out. Store insecticide containers out of reach of pets and children.

Schedule of Pest and Disease Control

Every 10 days, I give my greenhouse a regular allover spray­ing with an electric Devilbus sprayer. I also have a lightweight, inexpensive plastic sprayer. This holds about a quart of liquid, and can be operated with one hand. I keep it filled with malathion solution for quick dealing with aphids, caterpillars, and thrips. The tank-type sprayer, used in outdoor gardening, is also effective in the greenhouse. This is a cylinder with a hand-pressure pump. It has a strap to slip over your shoulder. It holds about 2 gallons.

Insects attack plants in different ways. Thrips scrape away the green tissue from petals, leaving tiny scars. Malathion ap­plied at 5- to 7-day intervals will kill thrips—adults and off­spring. Spider mites (red spider) cause yellow-and-brown areas on foliage. A spray of cold water is effective if your plants can stand it (African violets cannot). Otherwise, use Aramite spray one week, malathion the next.

Cyclamen mites twist and gnarl the center leaves of many plants. Remove infested plants from the greenhouse; if you must save them, cut out the affected areas, treat the soil with sodium selenate (in solution or capsules) or Endrin, and keep these plants away from the others until they show clean new center growth, a matter of 2 to 4 weeks.

Mealy bugs look like flecks of cotton. When you find only a few on a plant, touch them with a cotton swab dipped in alcohol. For heavy attacks, use a malathion spray.

Get rid of caterpillars and grasshoppers by spraying with malathion or a similar product.

You can clean up brown scale with Dithion or soap and wa­ter. The scales are slow-moving bugs and when young are light yellow. While they usually attack only smooth leaves, they will invade an overcrowded batch of hairy-leaved plants, such as episcias. When this happens, use the hand spray, making cer­tain that tops and bottoms and all parts of the rough-textured leaf surfaces are reached.

Fungus attacks show up in blackened buds and rotting stems and leaves. Many plants respond well when the affected parts are cut away and powdered Fermate is applied, or when soil and plants are moistened with Carco-X or some other excellent fungicide.

In humid seasons, slugs may be prevalent, hiding in dead and decaying material. The seeds fall out of any pod they nip, and this means loss in time and money. Sawdust containing metal-dehyde, sold as Snarol, can be applied to the soil to poison the slugs.

Nematodes betray their presence in various ways. Plants may have a stunted or wilted look, or there may be blisters on petioles and nodules on the roots. Until recently plants in­fested with root nematodes had to be disposed of, but V-13 and other soil sterilants and fumigants have proved effective against these pests. Since these products are poisonous, take care to use exactly as directed.

Spring Housecleaning

Every spring I houseclean the greenhouse, first moving all the plants outside to the shade of my lath house. I apply V-13 to the pea rock in the benches and on the soil under them, wash away algae with a Carco-X solution, and clean the win­dows. Clearlite cleaner, 1/2pound to 1 gallon of water, helps remove old shading compound and dirt and leaves the glass sparkling.

If your greenhouse is not attached to your house, you may want to fumigate it with a "smoke bomb" like Fulex. Use great caution.

While the greenhouse is empty, check and replace cracked or loosened putty and glass. Repair defective woodwork, benches, and walks. If yours is a heated greenhouse, have the plumbing and heating checked in summer; don't wait for a winter breakdown. After this thorough going over, plants are put back, and throughout the year, I watch closely for signs of trouble and deal with it promptly.

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