An Economical Hobby Greenhouse  for the Houston and Gulf Coast Area

Introduction

Although Houston and the Gulf Coast Area lie in an area known to be relatively warm year round, tropical plants intolerant of freezing or near freezing temperatures require winter protection from the various cold fronts that sweep through and drop temperatures below or near freezing for short periods of time. In order to ensure healthy continuation of growth for such plants, a hobby greenhouse is virtually a necessity for the serious plant collector. This page will offer useful advice on this subject in regard to design, construction, operation and maintenance of a Hobby Greenhouse suited for the Houston and Gulf Coast regions. Some practical tips based years of experience in Hobby Greenhousing by the author will also be provided. The following assumptions will be used to discuss this topic. A hobby greenhouse will not exceed 12x12' size, be used only for hobby/plant collection purposes, and be located on an average residential lot. The main use will be for over wintering tender plants or for display of collection plants that are not used in the landscape during the outdoor growing season. I will assume that the expense of building and operating a hobby greenhouse is a luxury to a family's budget and therefore a concern.  The  hobby greenhouse described here was a backyard, utilitarian type structure that lacked aesthetic appeal but was very effective in inexpensive to build and operate.

Design and Construction

Materials:

A hobby greenhouse can be framed in aluminum/stainless steel, wood, or any other durable product. The most important element is the clear covering which can be either glass, fiberglass, or polyvinyl. Unless the greenhouse is being constructed as an attached add-on to your home for use as a conservatory, glass is not a preferable alternative. It is the most aesthetically pleasant choice, but the easiest to damage.   Aluminum/stainless steel framing also generally is associated with attached greenhouses. Aluminum and glass are also the most expensive alternatives. On the other 24524h71y extreme, the least aesthetically pleasant and least durable product is polyvinyl. Its advantage is easy up and easy down when needed and not needed. Polyvinyl is also considered a temporary or seasonal greenhouse solution, but it does work effectively. Polyvinyl is used by most commercial nurseries because is relatively cheap. It also damages easily in severe weather. My choice, by deduction, is fiberglass - not any, but UV coated greenhouse grade fiberglass of fairly rigid thickness. The UV coated fiberglass blocks harmful Ultraviolet rays and produces a more useable, less damaging form of light. Corrugated fiberglass is hard to seal and has more surface area for heat loss, therefore I recommend flat. Since aluminum is much more expensive than wood and not as versatile for construction, I recommend cedar wood framing for a beginning greenhouse. Please note that chemically treated lumber can be toxic to plants when water drips over it. Treated lumber can be used for side supports and exterior molding, but never for roof beams or areas above plants. Any dripping from treated lumber will be toxic to plants below. An aluminum storm door works well with an wooden frame and is more durable over time.

Location:

Location is important from a heat conservation and light availability perspective. The most ideal location to the least ideal is: south, southeastern, southwestern, east, west, northeast, northwest, north. The south side obviously shelters the greenhouse from the cold northern winds and when the angle of light is lower on the horizon during winter, the south side captures more light during the shorter daylight period of winter. A greenhouse located in the middle of a yard without any barrier to the elements is the same as a fully northern exposed location. Although it would capture more light, it would be far less heat retentive. A location close to a circuit breaker box is best for accommodating electrical service to your greenhouse. Choose your site carefully.

Construction Tips:

The following tips assume you have chosen wood framing with fiberglass and chosen a more favorable location.  

• A hobby greenhouse should be aesthetically pleasing since it is a year round structure but used mostly in winter. Landscaping around it helps make the structure blend with the garden and yard. Location helps in this respect as well.  
• Greenhouse grade UV fiberglass comes in standard 4' wide rolls. Therefore, a framework that accommodates 4' wide panels reduces construction costs and complexity. This approach accommodates 8x8'. 8x12' and 12x12' structures where 4x4" side beams are positioned at 4' intervals. The same theory should be used in roof construction with 4' wide sheets overlapping at least 6" on the down slope to prevent leakage and provide a tighter seal. A single angled roof raised 18" to 2' toward the rear side is the least expensive and easiest to construct. Allow for a 12" overhang for drip control during storms.
• Windows should be plenteous to allow good aeration and cross ventilation during spring through fall. They can be either prefabricated aluminum sliding type or wood framed with fiberglass hanging on hinges. I chose the latter due to the cost factor and prop my windows open with 12" sticks. I also seal them tight in winter using exterior swivel braces. The door can be either wood framed fiberglass on hinges or prefabricated aluminum storm door. I chose the latter because they were inexpensive and more durable over time.
• All exterior wooden surfaces to which fiberglass is attached should be covered with 1x4 framing to tightly seal the fiberglass.
• The flooring should be 6" deep gravel stone, about 1/2 to 1" diameter, or pea gravel (1/4-1/2 in diameter) filling a sand bed cavity. Using an inorganic substance like stone allows for excellent drainage and aeration, which in turn prevents disease organisms from inhabiting your greenhouse, plus is effective weed control. The outer foundation can be concrete block, brick, landscape timbers, or poured concrete. The 4x4" side support beams should be dug and concreted 18" into the ground.
• Electrical appliances and accessories should include one or two grounded receptacles (4 plugs) , each receptacle controlled by a separate circuit breaker. Make sure electrical service meets all electrical codes. Also, a 12"-18" louvered exhaust fan should be installed to prevent overheating conditions. An 8x8' house can be sufficiently heated with one thermostatically controlled 1500 watt space heater. If a really hard freeze occurs, a hanging 100 watt frosted light bulb helps generate additional heat. An 8x12 or 12x12' size will need at least two space heaters. To install propane or gas heaters can add significantly to the expense . Since our really cold nights are few along the Gulf Coast, electric space heaters don't significantly run up huge electrical bills but are very convenient to use. The only risk is a power outage. I have found that placing a thick polyvinyl sheet or tarp over the top and trying it down along the sides can substantially reduce heating needs and keep a greenhouse warmer during severely hard freezes. This would be an emergency backup measure to consider. You should always have a contingency plan for emergencies and severe weather conditions.
• Use of space can be maximized by designing and building benches with 2x4's and using thick honeycomb shaped wire or 1x4 wood slats  to cover the top. This allows for good air circulation and more light to get to the plants stored at floor level. Benches should not take more than 1/2 to 2/3rds of your greenhouse space depending on the size plants you will be over wintering. Some plants need floor space due to their height. Hanging baskets from the roof beams also allows you to use more space efficiently, but be careful that they don't block too much light to the plants below.
• Whether you personally construct it or hire someone else to build it, take plenty of time up front to design your greenhouse to meet your personal growing needs and minimize potential problems and operating costs. An ounce of prevention beats a pound of cure. The size of the greenhouse ultimately limits or self disciplines the plant collector. You can't have more plants than you can over winter. It works for us.

Operation and Maintenance

The following tips are offered for operating and maintaining a hobby greenhouse along the Gulf Coast Area

• The smaller the greenhouse relative to your needs, the better and cheaper it will be to operate and maintain. Space can be maximized by cutting back all plants before putting in the greenhouse. Hanging baskets can be regenerated next growing season by taking and rooting cuttings in 6" pots rather than storing large hanging basket plants or by pruning back significantly, any larger hanging basket plant.
• Always do periodic inspections of plants during warmer days of winter to check for disease, insect pests, improper environmental conditions that may harm plants, etc. This may mean pulling them outside, removing dead growth and dropped litter, and visually checking each plant. Treat problems immediately. Insect pests and diseases can spread very rapidly in this confined environment.
• Remember that winter greenhouses can build up heat (greenhouse effect) therefore plants may dry out quicker than you might expect. Hand water all plants based on need. Plants at lower light, cooler floor levels could easily get over watered and rot in their cooler micro environment. All greenhouses have micro environments - be sensitive to that. Plants should be positioned according to these micro environmental conditions, Water plants in early to mid morning during winter months to avoid cold damp soil during the cooler evenings. During warmer days of summer, watering anytime is ok.
• Overcrowding can cause carbon dioxide deficiency and stunt growth. On warmer winter days, open windows to allow fresh air to circulate (windows of opportunity - pun intended!)
• Scrub greenhouse transparent surfaces at least twice a year (spring and fall) to eliminate algae buildup and dust (which clings easily to fiberglass especially). These buildups can reduce light significantly. Visually inspect the structure for any problems periodically. (e.g warping, rotting, etc.)
• Remove as many plants as possible during active growing months and leave the greenhouse open for good air circulation. I only use my greenhouse benches for potted orchids during the warmer seasons. Most tropicals prefer to be out in our great Houston heat and humidity from spring to fall. The big guessing game is "When is it safe to take your plants outdoors'? The rule of thumb we use for the Gulf Coast area is to have all our tender plants ready to put into the greenhouse by Thanksgiving and we feel relatively safe taking them out after the first official day of Spring unless the extended weather forecast calls for temperatures below 50 degrees on a subsequent night.

We now have a pre-manufactured, stainless steel 8x12' glass lean-to greenhouse that is much more aesthetically appealing and energy efficient, however, was four times the cost of the self designed greenhouse described above.