|
A heat source for your greenhouse depends on several factors with climate, plant type, size of greenhouse, and insulation materials being the four primary considerations.
Climate – The most important question to ask yourself is how cold does it stay during the day. In many parts of the country a simple electrical oscillating space heater will do the trick, but if your day time temperatures get below freezing you may want to look into something more powerful.
Plants – Different types of plants can withstand varying degrees of cold. For instance, typical houseplant prefer a temperature of about 53º F, but new growth and/or vegetables, especially tomatoes, need temperatures around 60-63º F. Orchids like no less than 63º F and seedlings require a very humid and warm climate during first week or two, 70ºF and above. Some blooming plants such as daffodils actually require a cooling off period and others are influenced by both temperature and day length. So it is important to do a little research about the plants you are trying to grow.
Size of Your Greenhouse - The bigger the structure, the more heat will be needed. In most conditions, an ordinary oscillating space heater with thermostat will handle any greenhouse of up to 100 square feet. Choose a slightly larger heater for 100-150 square feet. A 220 volt blow heater is recommended for structures that are 150-250 square feet. A good source for these is W. Granger. Propane heaters with exhaust systems are a more complicated option for large greenhouses, but the investment on the front end will save you money in the long run.
Insulation Materials – The two most common rating systems for insulation are R-value or K-Value. The R-value measures the thermal resistance of a material. It indicates the total resistance of a material to the passage of heat or cold. The higher the R-value, the better the insulation. The R-value is used most commonly in rating home insulation.
The K-value is the measure of heat conductivity of a material. That is, the measure of the amount of heat, in BTUs per hour, that will be transmitted through one square foot of material that is one inch thick to cause a temperature change of one degree Fahrenheit from one side of the material to the other. Unlike the R rating, the lower the K value, the better the insulation. If the K-value of the material is known, the R-value can be determined by dividing 1 by the K-value (R-value = 1/K value). When talking about greenhouse efficiency, the K-value is used.
The K-value rating for various types of greenhouse materials is as follows:
•Regular single pane greenhouse glass: 6.0
•4 mm Twin-wall Polycarbonate: 4.0
•6 mm Twin-wall Polycarbonate: 3.6
•8 mm Twin-wall Polycarbonate: 3.3
•10 mm Twin-wall Polycarbonate: 3.0
•16 mm Triple-wall Polycarbonate: 2.3
In my home garden I have the Riga, which has a K-Value of 3-3.3 as it uses 8 & 10 mm polycarbonate. It is heated with an electric heater which is performing marvelously during our unusually cold winter. To increase the efficiency of the insulation you can also use a shade cloth or a curtain at night.
One last thing to keep in mind is over heating. A big heater can make the inside of a greenhouse very warm, which might result in automatic window openers, opening up even during the night. Such openers need to be disconnected during the winter months – however, it is also very important to provide plants fresh air on a regular basis. Opening a window or door during the day time as needed – can be very important.
|
P. Allen Smith
Seed Starting and Lighting
Lighting is Most important in success with seeds indoors. Plants will be Spindly and wont grow without lots of light. Standard Florecent lights produce blue or red light. Blue- provides energy for photosynthesis and Red- initiates flower production.
Using both warm and cool lights will give a balanced spectrum.
More expensive growlights used by usu have 4 bulbs to a light with 3 cool and one warm. Using smaller lights with only two bulbs works fine also, the coverage side to side isn’t as good though. Try to keep light on a chain and 3 to 4inches above plant.
Seedlings require 14 to 16 hours of light a day, so a timer makes that a cinch. Some seeds require darkness and some light to germinate. Always read the lable on seed packet for germination light requirements.
Building lighted gardens can be fun and very accommodating to different space limitations. Lighting can be hung from raftors in unfinished basements, under larger bookshelves or aquarium stands, or you can create your own stands out of wood, PVC, or modify storage shelves. Most storage shelf units are adjustable and have holes to adjust the shelves. You can cut wood to the width of the shelf and hammer in nails in either side of it to slide into those holes. Then cut another skinny board to bridge to the board on the other side. Then hang lights from the long cross board. This is a great way to use storage shelves without having to drill a hole in the shelf above.
Germination Temperature varies by variety. Usually 70 to 80 degress is best. Some perennials like it cooler for starting, and some even need to be frozen for a time first. Its called stratification. Once plants are sprouted, its ok to grow on in a cooler place. I like to start my seeds in the warmest part of the house, then move them to the cool 50 to 60 degree basement for growing. Warmer temperature causes faster growth.
Perennials can be started as early as November, but most are fine Started in January and February. The majority of Annuals are ok to be started 6 to 8 weeks before the last frost. As plants grow, transplant to larger containers to keep plants from being rootbound. To get the largest Plants, keep moving to larger containers as roots reach the bottom of the container. Most plants will grow fine in 4 inch pots, but some aggressive plants do best in gallon pots.
When its time to move plants outside, its important to remember that your new seedlings have not had the temperature fluctuations or the light intensity that occur outside. Getting your plant used to that is called “hardening off”. You need to move your plant outside for only an hour in the shade the first day, then half day the second day. On the third day leave it out the full day. After that slowly moving it toward the sun each day will help the plant adjust with out killing it.
