Submitted by gsparrow on Thu, 04/02/2020 - 12:29
Betty Ann Addison

For half of my long lifetime, I have enjoyed the greenhouse attached to my home. Through long Minnesota winters it has kept me absorbed in encouraging new life, enjoying colorful flowers, and envisioning springs to come. As a child, I was enchanted by the magic of tropical wonders living year-round in the few greenhouses in our town on Long Island, New York. My mother’s house plants on every window of the house seemed just the shadow of a paradise that you could walk into.

My first greenhouse in Minnesota was a commercial one, only ten feet by ten feet (3 m by 3 m), gifted to me by a couple who were building a larger one. That should have told me something! Stuck on the east end of the house, it was soon outgrown, but it had served its purpose of whetting my appetite. Later, a fortuitous visit to England showed me one could – indeed should – go whole-hog with one’s dreams. My daughter and I stayed overnight with the owner of a small alpine nursery and his wife. They had a lean-to greenhouse attached to the south side of their home that extended all the way up to the roof of the second story.  All that moonlit night I kept looking out at it and dreaming about reproducing it back home. After all, my home faced south also. They assured me it was nothing but good for them, and in their mild climate, did not need much in the way of extra heat.

Once home, another fortunate encounter alerted me to discontinued, triple-pane patio door glass. The insulating value of three layers of glass was immediately obvious. The man selling them had a barnful in several different sizes.  In fact, he had built a greenhouse attached to his own home, so he could confidently recommend construction details. With much design help and cautionary tales from countless others, I was able to create a drawing of a “sun porch” to submit to the City. Because the south side of my house faces the street, in order to get a building permit, it had to present itself as an architectural feature of the house.  


General Construction:

The main part of my house is 40 feet (12 m) long and is a classic one-story rambler. Because the distance from the ground to the roofline is only 12 feet (3.6 m) there was not enough room for a good pitch for rain and snow removal, unless the structure was unacceptably narrow. A solid six-foot (1.8 m) extension to the existing roof, slightly pitched and built to withstand a heavy snow load, solved that problem without cutting down significantly on available light. The finished size of the greenhouse is 12 feet by 40 feet (3.7 m by 12 m). The transparent part of the roof is now polycarbonate. It is very strong, never damaged by hail or snow load and is lighter than the glass panels that were first installed. The glass slid down after a few years, leaving a gap that leaked. The pitch is six inches per foot, so anything more than a few inches of snow has to be removed with a roof rake to let in light as well as cut down on weight. Light snow can be melted off by turning up the heat up to 70°F (21°C) for a few hours.

The panes of the patio door glass are approximately six feet tall by 30 inches wide (1.8 m by 76 cm). There are 14 of them. Uprights to support the glass are made of 4x6 treated timbers. They are rabbeted on each side on the inside of the structure. After the glass panels were set in place, they were secured with 2x4s screwed to the uprights. No glue was used, so in case of breakage the panels can be replaced easily. Silicone seals the bottom of the glass on the outside where it meets the wooden sill plate and keeps rainwater from entering between the layers and creating fogged glass.

The ends of the greenhouse hold six foot (1.8 m) wide sliding patio doors, with sliding screens as an option, to discourage stray birds, cats and butterflies from entering when the doors are open. The balance of the ends is wood construction.

Because it is a permanent addition to the house, the foundation had to be below frost line, which is four feet (1.2 m) deep in this climate. In for a penny, in for a pound. One end of the foundation was dug extra deep and a well pit housing an irrigation pump and tank was constructed, making them safe from freezing. To enter, there are slide-away stairs, a trap door and narrow steps to access this secret room, only entered twice a year to turn the irrigation on and off. People have accused me of hiding bodies there, but not true!


The floor is hard quarry tile, laid on concrete over a two-inch-deep (5 cm) bed of gravel that holds solar heat. It is 10°F (-12°C) and sunny outdoors as I write, but the furnace has not gone on for most of the day.  Even on cloudy days, the greenhouse collects some solar heat and with minimum gas heat, stays about 53°F (11.7°C). On sunny days, it even heats the house with solar-heated air circulating through the open door at one end and a bedroom window at the other. When the hanging gas furnace is not blowing warm air, a standing fan creates horizontal airflow that stimulates plant growth as well as aiding heat distribution. But, on our cold nights (as low as -25°F/-32°C) and snowy days, heavy drapes at the ends of the structure are pulled, and the heater keeps the room in the 53 to 57°F (11.6 to 14°C) range. This is ideal for alpine cuttings, adequate for most tropicals, and even some orchids grow and flower at these temperatures.  


Never let it be said that something good is completely without care! What works in winter has the opposite effect in summer. Cooling is as important as heating. We aim to start bringing mature plants out of the greenhouse to the nursery by late April and empty it entirely by June first. In summer, the sun in northern climes beats down directly overhead. As early as February and as late as November, doors must be cracked or fully open to keep the temperature below 80°F (26.7°C). Many times it will rise to 90°F (32°C) before I notice. A large exhaust fan at one end and a power vent at the other, though noisy, save the plants from cooking if I must be away. In a heat emergency, liberally spraying water from a hose over everything – floor, plants, tables, and walls – lowers the temperature, raises the humidity, and saves the plants. Most of the time, opening the doors of the greenhouse and turning on the standing fan is enough for the comfort of people and the horticultural occupants. But in summer, even with the doors open, temperatures in excess of 100°F (37.8°C) are ordinary, so the structure is unused except in the evening or as a porch when it rains.  The door and window to the house are kept tightly shut.

If you are considering a greenhouse of your own facing south, shade cloth commonly available in 50% shade can be suspended over the roof or laid directly on it, to reduce the sun’s heat inside. Of course, greenhouses are built every day facing east, west and even north. The main advantage of a southern aspect is less cost for heating in winter. Other aspects need more heat in winter and even supplemental light but are less prone to overheating in summer.

Other Considerations:

Plants need abundant water.  A watering can just doesn’t supply enough. I found that a collapsible hose which extends the whole length of the greenhouse and shrivels up to basketball-size helps to avoid anyone tripping and falling. There already was a faucet on the wall of the existing house connected to the well, whereas the rest of the house is on city water. Plants do not thrive with water treated with chlorine and other chemicals, I have found. I improvised a sink with a plastic tub on a stool for soaking dry plants, washing containers and filling watering cans for fertilizing. Excess water is splashed on the bay tree or thrown outside when it is not too cold.

Plants get watered with a hose three times. The first watering soaks the top of the pot, the second the middle and the third time water should run out the bottom to be thoroughly watered.  If you are in doubt if the flat or pot is watered enough, lift it. It should be heavy. This technique uses lots of water to flush out salts, which land on the floor, eventually making a white deposit.  The contractor wisely built a slight slope into the floor, guiding water to a slot in the foundation to a French drain (gravel-filled pit) just outside. Once all plants are out in early summer, the floor is acid washed and squeegeed out, rinsed and dried, all set for a garden party or the coming fall.  Electric lights are necessary for the navigation of humans, but not so much for plants, I have found. When I want to water some evening, transplant rooted cuttings, or find some esoteric tool, a flashlight just won’t do. To get the most growth of seedlings, LED lights in the basement give the best results for the least amount of expenditure.  

Tables rescued from a thrift store were my first plant benches, but I’ve found folding plastic tables to be easier to put up and take down as the need arises. I cover all of them with a double layer of heavy plastic to protect surfaces from oozing water that somehow always gets through a single layer, staining or warping the tables.  Lately, we have set the flats on wooden 1x2 lumber for drainage.  This gives much better growth than when the flats sat in direct contact with the tables. Potting benches and supplies are out of sight, located behind a screen at the far (east end) of the greenhouse.  Bins of various mediums and boxes of pots are under tables there.  Soil mixing is done on a cloth on the potting table. The work area is adjacent to the back door that leads to the gardens and nursery.

The west end, right by the house’s front door, harbors a bay laurel tree, pink camellia, coral azalea, orange fuchsia, and a huge rosemary bush. All winter these flowering plants look inviting. Early and mid-winter, while there is still room, my friends and I enjoy sitting in the greenhouse, enjoying a cup of tea and conversation with classical music on the radio.

Using the Greenhouse:

Winter propagation of alpines is the main activity in the greenhouse.  We collect cuttings in the fall when many plants are having a celebratory flush of growth after the summer heat has receded. They are dunked in liquid hormone and planted in tight rows in a well-drained medium. Often, plants will have started to produce adventitious roots, making them divisions that don’t need a hormone treatment, so are even easier to propagate.  Many a special alpine has been saved and reproduced by wintering in the cool greenhouse.

Because of a large evergreen tree (Chamaecyparis pisifera ‘Filifera Pendula’) on the southwest side of the greenhouse, the west end is shady. All the freshly stuck cuttings start there and are misted at least once daily. Most alpine cuttings begin showing leaf growth after a couple of months, which indicates their roots are also starting to grow. When cuttings have some roots, they can obtain water on their own without daily misting to refresh their leaves. They are then moved to the sunnier, east end. Broadleaf evergreens need a longer time to produce roots, so they occupy the shady end most of the winter.

Divisions and cuttings begin to fill their original flats starting in January. Potting into 2.5-inch (6.35 cm) pots begins in February and continues through April.  Everything is fertilized once a week and put in the sunniest spots available. Flats are squeezed on hanging shelves, more tables are set up and even the floor is utilized for low light plants, giving three layers of growing space. Plants eat light, so it is not so surprising that as the sun gets higher they double and triple their size seemingly overnight.


Preserving and distributing rare and special alpines collected from long-gone sources and selected over 50 years in my nursery is my calling.  I am grateful to have this opportunity to share, and the greenhouse keeps the flow of life going through the seasons and years. 

In addition, all the joy this greenhouse has brought me and my friends is incalculable. It is the heart of my home and is an economical luxury. My heating bill is not much different than other homes this size. I feel it has been an investment in my health and well-being. Even though caring for it needs a certain amount of discipline, plants are my pets. Because it is attached to the house, not only is it heat efficient with only three walls, but there is an entrance from the house, so night and day I have easy access to soak up the sun or gaze at the moonlight on the snow.  I am so grateful for the experiences it has given me and would encourage you to think about making your garden dream, whatever it is, come true. As my late husband Charles Addison would say, “That’s a good idea; why don’t you do it?”