Greenhouses, Part 2

In the expanse of backyard soil, all the elements crucial to healthy plants acheive a balance on their own. But the greenhouse gardener must face a different set of challenges. Ventilation, temperature, water and humidity all must be managed. Traditional methods of getting heat to the greenhouse include tapping the home heating system, using a gas or electric heater, or solar heating. Because keeping the plants warm is the most expensive part of greenhouse gardening, attaching the greenhouse to the side of the house is especially attractive. Gas heaters are efficient, compact and fairly inexpensive to operate, but the exhaust must be vented outside. Uncombusted fumes can be deadly to plants and humans. Electric heating is mort than adequate but can be very expensive. Solar heating falls into two catagories; active and passive. Active solar heating system has external collectors and fans or pumps that circulate the warmed air or water into the greenhouse or into a storage. A passive solar greenhouse system is one in which the greenhouse acts as the collector of solar heat. This heat is then stored in an internal water or rock storage. Heat builds up on sunny days, occasionally building up to a temperature high enough to cook the plants if the house is not vented. Small vents can be installed under the beches to allow air to circulate There are termostatically controlled vents available that will open and close automatically and prevent overheating - whether you are there or not. Some form of shading, especially during spring and summer can be an effective way to keep excessive heat under control. Reflective paint, colored plastic film, or slatted curtains are easy to install and provide relief from intense sunlight. 

Because a pot in a green house is practically suspended in midair, there isn't a water table to offer additional moisture when the weather is dry. As a result the greenhouse gardener must know when and how to provide additional moisture. Inspect the soil surface, if it's dry to the touch when you scratch a half inch or so below the surface, a thorough watering is needed. With time and experience you may learn to tell when it's time to water by the color of the soil or by the sound of the pot when it's tapped with the knuckes. Schedule watering for the morning so that plants can dry off before nightfall. Watering in the morning means the plants get moisture during daylight hours when they grow most. On bright sunny days, the loss of water through evaporation and transpiration is greater than on cloudy days. So give plants extra water on bright days and less on cloudy days. Corse sandy soil cannot retain moisture as well as humus rich well-structured soil. Watering may have to be more frequent for sandy soil, so check pots often. Keep in mind that plants prefer too little water to too much. Roots stuck in swampy soil will suffocate. During the winter months, cold water directly from the tap may be so cold if will shock roots into temporary inactivity. Mix cold water with warm, the ideal temperature is around 60ºF. Because clay pots are porous, moisture rapidly leaves the soil and the plant. So more frequent watering is needed, or use plastic pots. If a garden hose is used, attach a bubbler or mister to prevent the soil from splattering. An uncomplicated and inexpensive way to maintain soil moisture is through a wick system. Wick material suspended in water reservoirs is inserted into flats or individual pots. Capillary action pulls water up into the soil. The amount of water supplied can be regulated by increasing or decreasing the distance between water source and plant containers. Flats are usually placed no more than 4 inches above the reservoir pans, while pots may be as far away as eight inches. For catering to the needs of individual plants, nothing beats watering by hand though.

There is more to watering than simply pouring water on soil. Plants loose moisture through small openings in their leaves.Trouble is, if the air is too dry, more water will be lost than can be taken in by the roots. The ideal humidity is between 50 and 70 percent. There is a device called a hygrometer that will indicate the humidity. Place it in a protected place. When moisture drops, replace it by sprinkling walks and floors, misting plants, installing a portable humidifier or placing pans of water under the benches.

More next week.


Tomato diseases

Verticillium and fusarium wilts are soilborne diseases that cause yellowing of the leaves, wilting and premature death of plants. These diseases persist in gardens where susceptible plants are grown. Once they build up, the only practical control is the use of resistant (VF) varieties.


You have heard about planting a garden to attract butterflies. How about planting a bee garden? By planting bee-attracting plants, you can attract a diverse array of other wildlife as well. Butterflies, wasps, flies, hummingbirds and other pollinators will give you a bountiful harvest of fruits, vegetables, seeds and provide you with many hours of outdoor entertainment. Use a maximum of native annual and perennial wildflowers which naturally grow in your region. These plants evolved there and are adapted to the growing season and local climate and soils. They often require less water, fertilizer and pesticides than showy exotics, fanciful hybrids splashed across colorful ads in the most recent seed or bulb catalogs. The native wilflowers will also provide your bee visitors with more nutritious pollen and nectar since plant breeders do not think about providing floral rewards for pollinators and their magnificient creations are often all show and no bee chow. You can also make selections from old "heirloom" varieties such as Cosmos, black-eyed Susans, lupines, mints and others which are now enjoying a Renaissance of popularity. Don't worry, nearly all species of bees are gentle and will not sting you. They are simply searching for food-- pollen and nectar-- to feed themselves and their young.



"Gardening is an exercise in optimism. Sometimes, it is a triumph of hope over experience."




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