The Greenhouse Effect

By Louise Oades, KCMG (Part 1 of 2)

Four years ago, I purchased a 6’x8’ Edenlite Greenhouse from Charley’s Greenhouses in Oregon. This is my haven away from the world’s hustle bustle, my Zen temple, my solstice.  It is a place where all of the 1990’s rush of everyday life leaves at the door and a peaceful coexistence begins.  Should you decide to purchase a greenhouse, whether for peace of mind or to beat the neighbors with the first plants, there are many areas to consider.

When choosing a greenhouse, there are about as many types, kinds, and varieties as there are homes.  The frame can be aluminum, wood, PVC plastic or steel.  Aluminum is cheaper than wood and requires no painting, but loses heat more easily than wood and condensation drips are a nuisance.  Wood is thought by many to be the most attractive, but rot resistant wood is expensive and care must be taken (alas, maintenance) to preserve the appearance.  Hey, fellow gardeners don’t waste your time on non-treated wood as your temple may collapse on top of you.  PVC plastic is exorbitantly expensive, requires little if any maintenance but isn't strong and may need metal coring.  Steel is the choice for many commercial greenhouses due to sturdiness but pits and rusts.  Styles also vary from lean-tos to conservatories.  My English mother-in-law’s reply to the difference between a greenhouse and a conservatory, “Basically a conservatory is more ornate, joined to the house, and the plants are grown for display.”  Interesting?  Does this mean greenhouses are for plants and conservatories are for people?  Since we are discussing greenhouse, I’ll leave that one for others to debate.

Shockingly, even avid gardeners such as me are awakened to find that growing plants in a greenhouse is different than growing from outside.  Not more difficult…just different.  This unique environment, where light, humidity, atmosphere, and temperature are all different from the outside yields new lessons in gardening techniques and pest control.   I once tried using my Mantis tiller on inside beds, quickly discovering the lack of oxygen and gaseous emission any small powered machine can cause in an enclosed area.  The enclosed space also limits the use of any “smelly” chemical.  Remember that vinegar is acetic acid, thus a chemical.  So when I refer to chemicals, I am not necessarily referring to those manufactured by an agricultural company.  Your use or nonuse of pesticides and insecticides is up to your good judgment!  Too much of anything in a small enclosed space can fumigate you!  Letting “good” insects reduce “bad” insect problems (IPM: integrated pest management) is a good choice in a greenhouse due to such a confined space.  Rodale’s guide to insects sits next to my water mister for easy reference.  Everyone who spends time in a greenhouse becomes a botanist, an ecologist, and an entomologist.

Although my greenhouse would be correctly termed a “Cold” one, even the seasons it can be used in reflect the differences from outside.  A cold greenhouse has two true growing seasons, spring and fall.  Summer and winter in a cold greenhouse are difficult to control as the greenhouse isn’t artificially heated or cooled.  There are four types of greenhouses, cold, cool, warm and hot, with variations among the three.  A cold greenhouse heated in the spring for propagation becomes a “cool” greenhouse.  My cold greenhouse becomes a hothouse in the summer due to natural causes of West Virginia weather.  It is said that every greenhouse is different.  Common sense tells us all this.  But the location of the greenhouse (i.e., the climate zone and even the location in one’s yard) along with the orientation impact the microclimate inside.  Site choice may not be as viable an option in our state with its hilly terrains as in the heartlands.  With limited selection available, try to choose a flat area without trees close by to provide some protection.  If you’re one of the lucky one with some flat land, face your lean-to on a west facing wall and your free standing greenhouse so the ridge runs east to west.

Protection from too much sun, too much heat, or freezing temperature are but a few areas to address in a greenhouse. Light and temperature are two of the most important factors to consider.  Both commercial and home greenhouse must account for the limited space in a greenhouse – planting and timing are crucial.  Too many plants impact the rest as they will compete for light with others in a confined space.  In the early spring, try placing white boards on the work bench to help reflect light to seedlings.  In general, place seedlings that are to become tall in areas that receive more light – the bigger the mature plant, the more light it requires.  Slow, spindly growth, yellowing of leaves or plants leaning toward the light may be signs of light deficiency. (One must be careful, whether in a greenhouse or not, in making generalizations.  A diagnostic approach should always be taken. One or two symptoms may not yield a correct diagnosis as there are many similar systems.  As overcrowding is a general tendency of mine, and I have determined the above system to be on living physical factors, I am listing these as an example).  Supplemental light has improved tremendously over the last few years incorporating the red and blue spectrum into grow bulbs thus providing plants the requirements needed for photosynthesis.  I use a grow light for germinating seedlings in early spring where the lights can be at close range to provide enough “foot candles” or light intensity to do a proficient task.  The environment in a greenhouse changes throughout the seasons due mainly to changes in temperature and light.  In a cold greenhouse there are three seasons, winter (cold), summer (hot) and spring/fall (temperate).

Summer and winter greenhouse require more a drastic, but differing, measure to control temperature and light. Similar problems occur in any greenhouse that is either too hot or too cold, plants are slower to grow and more prone to insect attack and disease.  I use an inexpensive bubble insulation to keep the greenhouse above freezing and extend the usable season.  If my greenhouse were larger I might consider placing drums inside which would be painted black to absorb heat on the side facing outside and white on the inside to reflect the light.  Unlike climate controlled greenhouse, my cold greenhouse is used to winter over many plants for all but the coldest four or five weeks, at which point I move all plants into our heated garage.  The problem, however, is not just the cold but the humidity in the greenhouse during that four or fie week duration.  Trying to keep warmth inside hinders air filtration from outside as I limit opening and closing vents and odors to conserve heat. The small heater runs what seems to be nonstop and, of course, humidity increases above the desired 40 to 60 percent thus I increase the chance of losing my plants to disease.

Look for part 2 of Louise’s greenhouse article in the next issue.