Greenhouses

The original plan for our operation was to construct a 44' X 128' double bay gutter connect style greenhouse. For one reason or another, we ended up purchasing a  30' X 120' ground-to-ground greenhouse. This was probably the best decision that we fell into. All of the components of operating a commercial hydroponic greenhouse are present with this size house without the up-front cost and risk of a larger house.

Greenhouses come in many designs and sizes and are manufactured by many people. I found a local manufacturer totally by accident. There is no telling how many times I passed the plant without ever knowing they were there. A local vendor is probably the best route to take if you and he know the specifics of a good hydroponic greenhouse design. A greenhouse designed for horticulture production is not suitable for most hydroponic applications.

The two main styles used for small scale hydroponic ranges (less then 10 acres) are the ground-to-ground (Quonset) and gutter connect. The ground-to-ground offers smaller sizes and lower costs. The main disadvantage of this style is that the arch extends from ground-to-ground. This creates a space problem on the inside walkways adjacent to the arches.  A variation on the Quonset is a free standing type. This is basically a Quonset house with a small side or wall added. This side provides for more clearance on the inside of the house adjacent to the arches. The gutter connect styles can be a bit more costly but they offer better construction design (they actually have walls) and are expandable. In either case, be sure that your house is designed to handle the wind/snow loads that are common for your area.

Other components that I feel are essential for the operations are heating and cooling, ventilation, coverings, plant support systems, irrigation, and controls.

During our research towards this project, we had the opportunity to talk to and visit with many greenhouse operators. They all seemed to add a particular influence in how we constructed our house. The main point that I must stress is that the better your house is engineered, the more efficient it will be to operate. If you simply start erecting arches, slap two end walls on it and stretch some plastic over the top without determining the exact size of heating, cooling and ventilation equipment, you will be in for a rude awakening with a whole host of problems.

Talk to manufactures about their designs and special features of their equipment.

Our Second House

We began construction of our second house in May of 2000. This house was originally designed for bolting to parking lots for retail operators. A good friend of mine who is also in the business happens to be an agricultural engineer. He took the original design, modified it to accommodate our needs and asked the company to build it. Considering we had no construction drawings, we managed to put together a pretty good double bay greenhouse.

Buying Used Greenhouses

I receive many calls and email from people asking about used equipment. My first house was used so I'm not totally against it. One of the main considerations to account for is what the house was originally designed for. Horticulture houses are much different from tomato houses. You can not hang tomato plants from the truss supports on a typical horticulture house and the column spacing is usually too far apart on a horticulture house. These are just a couple of issues that you must consider when looking at used equipment. Even some "tomato" houses fall short of a good design so if you're unsure about the equipment that you are looking at, ask someone to help you out.

Recent Issues in the Industry

The concept of a naturally ventilating greenhouse is being bounced around by several people from academia to suppliers. For those of us below the 5000' elevation mark and especially if you are in the South. Forget it! Here's why.

Most people that are proponents of naturally venting house usually start of with something like "since hot air rises...." and continue on with their pitch. In fact that very point is the reason why it will not work.

"Hot air" is only hot relative to other air. For example, if all the air in a room is the same temperature, then none will rise. If you can imagine a balloon filled with hot air and placed in that same room, theoretically it will rise. Let's keep things simple and discount the weight of the balloon, other air movement, etc.

So we have a sample of hot air rising in our room. If the room temp is 70°, the balloon will have to be hotter. Right? That's to say that the "hot air balloon" is only hot relative to the air temperature in the room. Now let's move this to the greenhouse with some real numbers.

If the air temperature outside (ambient air temperature) is 90°, then air in the greenhouse will have to be hotter then 90°. Herein lies the problem. Your greenhouse will have to be at least 90° to begin to move air! At this point, your tomato crop has already suffered. There are other factors that contribute to a vented house but if you get the concept of "hot air rising" they will not matter either. Never mind the direction of the vent! I've seen days here in Montgomery where the only air movement is from the cat breathing.

Further, hot air rising is passive movement unless you are talking about the dynamics of a full blown tornado. Tomatoes need air movement across them to prevent disease, keep the plants dry, replenish carbon dioxide, etc.