Nature is seldom cooperative with the greenhouse gardener in the winter.
We need a lot of tricks, including the benefits of modern heating and ventilating methods, and we must stay alert to the possibilities of using the few days of good growing weather advantageously.
As many greenhouse amateurs have learned, one slip in the supervision of winter heating, ventilating, or watering can spell disaster.
Understanding Greenhouse’s Heating Equipment
The size of the heating equipment in your greenhouse is something you probably studied carefully when the greenhouse was built.
It is a technical subject best solved by the experts in this business.
There are some things, however, for the owner to understand for himself.
Ways of figuring out the potential heat loss (indicating the heating capacity required) in BTUs are given in the table below.
If the temperature threatens to go below the low mark upon which your greenhouse heating was based, then auxiliary means of heat will be needed.
Too much rather than too little heat may pose the most significant problem.
The sun’s long rays pass through the glass and are trapped in the greenhouse, sometimes heating it on a clear day to a dangerous level.
There are two ways to reduce this natural winter heat:
- Ventilation
- Shading
Orchids and many foliage plants require light shading during the winter, but practically all others need all the winter sun they can get, so ventilation is the best way to reduce the temperature.
Ventilation
Unless you can be there all day or have someone there, manual operation of ventilators is almost impossible.
Automatic vent operating motors are an amateur greenhouse owner’s best investment.
Usually, these motors are stall-type damper motors that operate on a 24-volt circuit to open top ventilators weighing eight to ten pounds.
They are controlled by a thermostat, which should be set to open the ventilators when the temperature rises to a maximum temperature of 80° degrees Fahrenheit.
In late winter, the ventilators will open and close many times a day, giving a far more uniform temperature in the greenhouse than if the vents were operated by hand.
During winter, the roof vents are the only means of ventilation required, but as the weather becomes warmer, the side vents should be left open during the day.
The greenhouse temperature will drop rapidly as night falls after a sunny winter day. A rapid rise in humidity accompanies this sudden temperature drop.
In a tightly closed greenhouse, these conditions favor the development of fungus diseases.
The best preventative against the start of illness is air circulation, so it is essential to leave a side ventilator partially open.
In mild weather, it may be left half empty all night. In the coldest part of winter, it should be left open an inch or two.
This does not increase heating costs much but makes a difference in the greenhouse atmosphere.
Old-time conservatory gardeners trained in the old world tradition could walk into a greenhouse at night and tell by the smell if conditions were right for good plant growth.
A heavy dank odor means stagnant air and high humidity; the scent of a good atmosphere, although hard to describe, is buoyant and earthy.
Essential Water
Water is perhaps the essential element in plant growth in its two forms, a soil-borne liquid, and an air-carried vapor.
Have you ever seen the beautiful flowering maples (abutilon) or shrimp plants (beloperone) grown in a farmhouse kitchen?
Here the humidity, reduced night temperature, and light conditions are appropriately combined to give the right atmosphere for these plants, which flower best under low light intensities.
The farmer’s wife may credit her results to a green thumb, but the success of the plants is a clue more to the environment than to her skill.
Humidity in the greenhouse should average 30% to 40% percent during the winter. When unlimited heaters are used, this value is maintained automatically.
With a boiler and radiation heat, or a vented space heater, it may be necessary to use a humidifying device or a pan of water on top of the radiator to produce a higher humidity.
Green plants should be watered when they need water and not again until they need it. I admit this is not a very lucid statement.
Still, the water requirements differ so widely between species of plants, and conditions determining a plant’s need for water are so uncertain that no precise instructions can be given.
In a cold, cloudy period in midwinter, a plant may require water once a week. It may need water every day during a sunny week in early spring.
Fortunately, experience in the knack of greenhouse watering comes quickly to an amateur greenhouse operator.
If you water thoroughly when the soil seems dry, then wait until it again seems dry, you will come close to nature’s spring routine of heavy rains followed by dry periods.
Tips For Winter Greenhouse Operations
These tips for winter greenhouse operations have been given without reference to the needs of specific plants.
Each plant prefers heat, light intensity, air circulation, and moisture.
For tremendous success in your greenhouse, study the plants’ requirements, and do your best to give the plants those conditions.
44659 by Cornelius Ackerson