Preparing for Greenhouse Setup
Grading, piping, gravel, concrete and electrical preparation all help you get ready for the greenhouse. Concrete slabs aren’t a structural component of the greenhouse but are a really nice addition. A slab can be floated in after the columns/stubs are set around the perimeter. Most people will use crushed gravel. Road base material can be watered and smoothed almost to as nice a surface as concrete for less than half the cost.
How will you heat the plants?
Floor heating is another thing to keep in mind — save yourself in overhead with root-zone heating. Air-fired heaters get 30-35% of the heat to actually reach the plants. Floor or bench heating makes that 95%. That makes a huge difference in quality and yield stability.
So, the trucks have arrived, the pad is ready and the process can begin. We move onto the installation process. A reputable greenhouse company should offer parts that are punched, pressed, pre-drilled, pre-bent and ready to assemble. The hidden cost of some lower-priced greenhouse frames is you will have to hire contractors to do the grinding, welding and drilling, which can increase overall costs and time.
As the assembly comes together, electrical work can begin—wiring, fans, vents, lights and blackout systems. Once all these things come together, the installation process comes to a close and the growing can begin.
Welcome to Greenhouse and Light Dep Growing
Growing in the greenhouse is a whole new ball game. Centuries have brought us the art of growing when it is cold, but what about when it is hot outside? Moving out of the greenhouse in the summer months is what some folks do, but in my opinion, that’s not an option. The secret is in the selection of the cover or glazing. Clear glass, polycarbonate and films sound like the right choice for winter, but if you’re in a warm, sunny area, the clear materials are going to mean heat challenges.
Typically, we would exchange the air with exhaust fans, but they cost money to operate and might not be able to keep up. Someone might suggest you get an evaporative cooling system or a wet wall. That works for some specialty crops, and we’ve seen the adverse effects of too much moisture and no cooling. It has benefits for certain regions. For example, the average relative humidity in Oregon or Washington is much different than in Arizona or Colorado. These factors in particular can cause a person to re-think the available equipment.
Relieving Plants When It Gets Too Hot
Back to the cover. Since clear covers can encourage too much light during the summer, I recommend a diffused material. Diffused polycarbonates and polyweaves tend to help encourage optimal sun values while blocking out un-wanted rays like UVB. Typically, shade cloth can help reduce UVB exposure, but it does cut the growing area off from par. The black shade cloths can also encourage more heat than relief.
Greenhouse covers are not the only source of relief in a greenhouse. A cover is designed to cool a plant’s leaf surface, and air temperature and humidity are also factors. While air temperature can remain high, it’s the solar gain that needs to be addressed. Solar gain, or the greenhouse effect, isn’t what we’re looking for on a hot day. The simple answer is to open up the greenhouse. Use the sidewalls and roof vents for the best natural airflow. Keep a close eye on the transpiration rates in plants.
Overheating and How to Prevent It
When a plant overheats, it begins to transpire by taking water up from the roots into the leaves and expires from the underside of the leaf. It’s a natural process, but it can also inhibit the plant’s growth. Hot leaf surface and soil temperatures add to this cycle. Another contributing factor to heat is the colors in a greenhouse. Black ground cover and black shade cloths tend to encourage way more heat than what a plant or soil can handle for effective growth. Add a black grow bag or container and you’ve got a solar oven. I believe in offsetting these colors with white groundcover, white shade cloth and tan grow bags.
These small steps actually equate to several degrees difference—a difference that saves water usage and encourages better growth.
Circulation fans are the key to helping provide fresh air with less dead zones. Circulation fans are best at moving air in a direction rather than scattering the air. When the air moves in a direction, we can see a dying affect in more humid zones and also a cooling affect for the plants. When air passes the underside of a leaf, it has a cooling affect much like a radiator in a car.
Plants and people are similar in the sense that blood runs through our veins as water runs through the plant’s system. That moisture may not be visible, but it’s there, and as air blows across it, the cooling process is achieved. Plants are easier to cool than the air in most cases.
Outdoor and Indoor Differences with Water and Heat
Indoor growers typically pay close attention to the reflector. The reflector or hood is what spreads the light. Some are more uniform than others and can have trouble spreading light, thereby creating hot spots that increase leaf surface temperatures and encourage higher transpiration rates. The result is typically yellowing leaves that start to appear. Stress begins to set in and bugs and pathogens easily take over. This happens because of inconsistent leaf surface temperatures.
Outdoor plants droop in the afternoon because of water weight, but indoor plants tend to yellow. The air conditioners and air-cooled lights won’t let the water weight gather enough. It’s almost like the plants can’t decide what to do, so getting sick becomes the end result. The sun is the ultimate indoor light. It needs reflecting and dispersing for certain crops in warmer regions. Good airflow and a proper cover is the first line of defense.
There are many considerations to make when planning a greenhouse. These are only a few of the many suggestions that go along with building and growing in a greenhouse.