High quality plants don't grow by themselves. The environment has to be just right. That can mean different things to different people, but primarily it refers to evenness in plant growth - getting the leaves, flowers and fruit to be the same size and shape from plant to plant.
Until the mid-1960s, this was a particular problem.
Then in 1967, Dr Jay Koths from the University of Connecticut invented a system that changed everything. Until he came along, there were a number of problems that prevented this from happening.
Causes of uneven plant growth
There were three main causes of uneven plant growth: inconsistent temperatures, concentrations of moisture on plants, and the depletion of carbon dioxide in the vicinity of them.
Before Koths' magic system was put into place temperature pockets would form. The warmest air would be in the centre of the glasshouse, away from the doors. Here the glass was sealed tightly in the frame and the windows were opened only when it became too warm inside.
Near the ends of the glasshouse, the temperatures were much lower, partly because this is where the doors were. Every time someone went in or out, warm air went out and some cold was let in.
Concentrations of moisture on plants
Stagnant air also meant that there were pockets of moisture. Cold air holds less moisture than warm air, and so where it was coldest, condensation was most likely, not only on the glass but also on the plants.
Depletion of carbon dioxide
Plants need carbon dioxide to survive. They use it in the process of photosynthesis; but they also use it up. In stagnant air, pockets of air with higher concentrations of oxygen than that which benefits plants form, and this, too, contributes to unevenness in plants.
Growing high quality plants
Koths demonstrated that if the air inside of a glasshouse could be kept moving that plants would grow evenly. That's because the interior temperature would be more uniform. It was also because moisture no longer stayed on plant leaves. Instead, a drier micro-climate was created as the air moved around.
The same mixing also replaced the oxygen "exhaled" by plants.
What was Dr Koths' secret? Fans.
By installing fans above the plants, even plant growth was achieved.
Nowadays, it seems like the obvious thing to do, but back in the '60s, it was a novel idea.
In America, heaters can sometimes be used to replace fans; but in Britain the one is bolted to the other.
Whatever method you use, placement is essential. Fans should be installed just below the ridge of the greenhouse if possible. That's because it's the place where the warm area is likely to collect. They need to be kept away from greenhouse walls, and there needs to be sufficient space around them so that air can be drawn in from the back and expelled from the front.
How many do you need? The rule of thumb is to multiply the length of the greenhouse floor by the width by two. So a greenhouse with a floor area that is 30 metres by 50 metres would need enough fans to shift 3000 cubic feet of air per minute.
Remember, the goal is to keep the air moving, and so that means that you'll have to run those fans 24/7; otherwise the air will slow down or stop moving altogether, pockets of differing temperatures and moisture will form, and what would have been high quality plants, will start to deteriorate.
And finally . . .
One last thing. It's essential that you keep your fans clean and well-maintained. Lubrication is less of an issue, but dirt can easily cause the motor in a fan to overheat.
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