JARS v50n2 - Building a Custom Greenhouse in Oklahoma

Building a Custom Greenhouse in Oklahoma
Leonard O. Miller, D.D.S.
Grove, Oklahoma

After living through the agony of watching my early blooming azaleas blasted by a late freeze year after year, I wanted to control Mother Nature. I live on the plains where temperatures can change very rapidly. Could I change the weather? I really wanted to grow Satsuki azaleas and USDA Zone 8 and 9 rhododendrons as if I lived along the coast of Oregon. I remember one year I put 7,200 square feet of Visqueen over my plants to prevent freeze damage; it didn't help. I decided to add a greenhouse that would allow me to control the environment.

My first thought was to hire an architect. One came out to see the site and discuss my dream. All my ideas had him questioning my sanity. We parted company, and I'm sure he felt relieved that he did not have to draw my dream. I spoke to glass enclosure salesmen, and their quote was way over my budget, as was the architect's. Rhododendrons are large plants and require some space, so I settled on 60 feet by 27 feet, which was the width of my house. My cash on hand was $50,000 so my project had a base expenditure of $31 per square foot. My finished project ran over this amount by 20 percent. I hope this article can help you decide whether to build your own controlled environment greenhouse.

I chose to be my own architect and general contractor. I was raised in a construction family, and this gave me the nerve to start on my own. After talking to a greenhouse equipment salesman, I was told the best roofing material was a ⅝ in. thick, triple-wall polycarbonate. This material is 200 times stronger than glass. It has a 10-year guarantee against light transmission degeneration and a 5-year replacement value on hail damage. The superstructure would be galvanized 10 in. steel beams with 2 x 10 in. treated wood rafters on 3 ft. centers. The structure was designed to hold 20 inches of snow, but I don't want to test its strength.

Leonard Miller's greenhouse under 
Greenhouse under construction.
Photo by Leonard O. Miller

The south and north wall would be sliding glass doors. The prevailing winds are from the south. The east wall is the west porch of my house, which has a 3 ft. elevated concrete floor. The wall of the house, which is wood, was treated with mildew resistant paint. The west wall of the greenhouse is a 17 ft. high rock wall. Rocks were laid on the side and on edge to provide planting areas.

The crew was a carpenter and his helper, a stone mason, a concrete finisher who poured the footing, a heavy equipment operator who put in the drainage lines, cleared the land and placed the large stones, the electrician and lastly a pump and water sprinkler installer. I did some of the plumbing and fabrication of the streams and waterfalls myself.

Leonard Miller's greenhouse one 
year after completion
Leonard Miller's greenhouse one year after completion.
Photo by Leonard O. Miller

The greenhouse contains a 20 x 10 ft. by 4.5 ft. koi pond and three waterfalls. There is a 3 x 8 x 4 ft. sump that collects the 8 ft. waterfall and a 4 x 8 x 4 ft. lava rock up-flow water filter. All water areas were plastered and treated with a concrete water proofer. After one year, I do not have any water leaks. The koi pond has 6,000 gallons of water. It provides humidity and cools and heats the greenhouse in its extreme temperature changes. A one-half horse pool motor circulates the water like a swimming pool. Water is aerated by the bubbling of water down the face of the rock wall and by a jet in the pond. Water is released by valves at all low points to rid the pond of any debris. However, the pond cannot be drained completely to prevent dry docking the fish.

R. christianae x R. macgregoriae
R. christianae x R. macgregoriae
Photo by Leonard O. Miller

The greenhouse is landscaped with elevated berms, mounds of pine bark to grow any acid loving plants. These beds are planted with vireyas, azaleas, and large-leaf rhododendrons. Seasonal plants are primroses in the winter and begonias in the summer. Tropical plants find a place in the greenhouse in the winter and then moved to the yard in the summer. I have planted vireyas on logs of white oak that I have cut. By planting in this way, more plants can be used for the same amount of floor space. Vireyas are also planted as lithophytes (plants on stone). There are 42 tons of stone used to create a feeling of a Japanese garden. These stones give sharp drainage to the vireyas under an abnormal wet condition.

Here in Oklahoma, the summer can be quite hot, including the nights. Temperatures can read 105°F for several days in the summer. In view of this, I needed both a watering system and a cooling system. The greenhouse was fitted with a shade cloth. The total shade with the cloth and the light loss in the polycarbonate is approximately 70 percent. This helps to cool the house and prevent leaf burn. A sprinkling system waters the plants twice per day during the hot weather. Watering is done once a day when using the mist system.

R. loranthiflorum on suspended log. R. lochiae
R. loranthiflorum on suspended log
Photo by Leonard O. Miller
R. lochiae
Photo by Leonard O. Miller
Near black foliage of 
R. beyerinckianum
Near black foliage of R. beyerinckianum
Photo by Leonard O. Miller

A cooling system was installed using a high pressure mist system. At 90°F, the water pump compresses the water to 800 lbs. per square inch. The droplets emitted are one-tenth the size of a human hair and create a mist that both cools and provides humidity. The lower the outside humidity, the more the temperature will be lowered. Many high altitude plants do not survive our summer heat. This cooling system may offer the environment for such difficult plants. Some of the plants that I am growing are vireyas, Rhododendron 'Maxine Childers', R. 'Taurus', R. 'Trude Webster', R. 'Horizon Monarch', R. 'Markeeta's Prize', John Thornton's R. hyperythrum hybrids, R. 'Johnny Bender', R. 'Tanyosho'*, R. pendulum , and Agapetes serpens . The hybrid vireyas seem to be making the most growth.

A special thanks to Kathy and Lucy from Bovee's Nursery for helping me with these special plants.

Leonard Miller, D.D.S., a member of the Ozark Chapter, is District Director Elect for ARS District 11.

* Name is unregistered.