IS IT feasible for a homeowner to install a solar greenhouse on his property to grow vegetables during cold weather? According to research at the University of Rhode Island's College of Resource Development, the answer is a qualified "yes" for New England home-owners. Presumably, it is even more practical for other areas where the climate is less severe.
After months of study that began with construction of an experimental solar greenhouse, the researchers concluded that a similar solar structure in an exposed location can serve as a suitable vegetable crop-growing environment as long as there is some supplemental heat when outside temperatures dip to zero degree Fahrenheit. The study also shows that a home solar greenhouse is capable of storing extra heat, enough, most likely, for use in home heating in the fall until mid-November and in the spring from mid-March on.
With help from the Governor's Energy Office, Prof. Charles McKiel, agricultural engineer, and Dr. Richard Shaw, floriculturist, added a 10-by-20-foot experimental greenhouse to a fieldhouse located on the college campus.
A double layer of fiberglass glazing was installed at a 60-degree angle on the south wall. In addition to the greenhouse materials and foundation, ten 55-gallon barrels of water and about 11 tons of crushed stone were used to provide a thermal mass for heat storage.
Along the south wall, a 4-by-20-foot area was reserved for growing vegetables that were either seeded or transplanted in late September and harvested throughout the season. Second plantings to replace harvested or frosted plants were undertaken as needed to make full use of the rectangular growing area.
Under normal cold weather conditions, the greenhouse remained above freezing without supplemental heat. But during a cloudy, sub-zero siege, temperatures in the greenhouse plummeted to a low 23 degrees from late December through early January, and tomatoes and cucumbers died.
According to the researchers, a supplemental heat source, such as a portable heater, should be used on days when it is extremely cold and cloudy. A blanket of polyethylene over the crops could eliminate the need to heat the upper level of the greenhouse at night. In addition, planting crops in containers that can be easily moved inside the home could reduce crop loss.
Crops growing in the front portion of the greenhouse tend to shade the water barrels, thus reducing the amount of heat that can be stored; if the positions of the barrels and crops were reversed, it would permit more heat storage, but then the crops would be shaded and their growth diminished, according to the research report.
Solar greenhouse vegetables will be less fully developed because the shorter winter day reduces the amount of light that gets through to the plants, according to the report. Carrots and lettuce are best; they require low light intensity and tolerate a lower temperature as long as that temperature is no less than 40 degrees. December, January and February are the worst months.
The 10-by-20-foot unit built by URI cost about $1,200. The cost can be lowered by using wood for the frame and salvaged barrels to collect the heat. Once the initial construction is completed, there is very little maintenance involved, except for occasional painting and weather stripping, the report says.
Q. My red raspberries bear a crop in the fall and another in late spring on the same canes. I have been advised to remove these canes in early spring. Doesn't it mean loss of the late spring crop?
A. New canes that come up in the spring bear a crop in the fall and again in late spring further down on the cane. The canes then die. Many specialists recommend that the canes be cut off at the ground level after the fall crop is over or early in the spring. You give up the late spring crop but get a far more bountiful fall crop.
Q. Can you tell me how to make my Christmas cactus bloom? It hasn't bloomed for several years.
A. Flower buds develop if it gets a night temperature of 50 to 55 degrees; also with a night temperature of 60 to 65 degrees if the plant gets 12 to 13 hours of uninterrupted darkness at night; at 70 degrees there will be no flowers regardless of length of night.
Q. Can herbs be grown indoors? If so, which do best?
A. Parsley, sage, English thyme, caraway, sweet marjoram, summer savory and sweet basil do best grown indoors on a sunny windowsill.
Q. I plant a row of spinach in the spring every year and every year it goes to seed. What am I doing wrong?
A. Most likely you are planting it too late. Spinach is a cool-season crop and will go to seed after the weather gets hot. You should have better luck planting it in midsummer for a fall crop and a spring crop for next year.