What are the considerations for growing over winter?

Heating, interior tunnels, air circulation, humidity control

When someone is intending to grow in a plastic covered greenhouse over winter, the first order of business is to put a double layer of plastic with air between.

This cushion of air acts as insulation and will reduce heat loss by about 30%. A secondary benefit from this cushion of air is that it reduces condensation in the greenhouse dramatically.

Even if you are not going to heat the greenhouse, it makes sense to put the extra layer of cover with air between since it will provide a significant extra margin for cold.

The small fan which puts the air between the layers is made to work against pressure. It can not “over fill” the cavity.

When installing the second layer of plastic, it is not pulled tight. This allows the second layer to puff up to about 10 cm which is the optimum space.

It is the dead air space that creates the insulation value. If the air is moving, you will not have optimum efficiency. This is the reason it is important to be vigilant about patching any holes in the plastic when they occur.

Especially if your intention is to grow without heating, you could benefit from installing and using small interior tunnels. These tunnels would only be covered during severe weather. Since the air volume is small, even the heat from a few light bulbs will make a difference.

Interior air circulation is even more important in the winter time than it is in summer. In the winter time when things are more likely to be closed up, the probability of stagnant air is high.

It is important to monitor the humidity level in your greenhouse as well. Getting rid of excess humidity will cost you some heat, but you are creating a healthier environment for your plants.

If you are using a forced ventilation system for either humidity or heat control in the winter, it is important to have the thermostat close to the incoming air so that things will shut down quickly if the incoming air is extremely cold.

Any heating system which is used in a greenhouse should have a stainless steel heat exchanger and burner. The standard aluminized units simply will not stand up long term in the moist environment of a greenhouse.

We hope you have found value in this series of posts, helping you prepare for your new growing adventure! Reminder that the deadline is May 31st for Fall Delivery. We look forward to working with you for your projects!

Infrared Plastic Coating

Another variation on greenhouse plastic is with an IR (infra-red) coating.

  • The IR plastic can reduce your heat loss by up to 20% over a regular double poly installation.
  • Even though this plastic has a hazy look to it, the light transmission properties are actually a couple percentage points better.
  • This plastic comes standard with an anti-condensate coating which means there will be less dripping in the greenhouse.

All of these features make IR plastic an attractive alternative for many people in spite of the fact that the cost is roughly  20% more then regular plastic. This plastic does not have an inside or outside.

The cell structure that the Infrared plastic is made from is significantly different from the regular plastic. This gives the plastic a much softer texture and feel and contributes to it not being as strong as regular plastic. This is why we suggest that it only be used as the inside layer of a double plastic installation.

The slight restriction for people with shorter greenhouses is that the IR plastic only comes in 100′ and 150′ rolls. You would either have a friend who can buy/use the extra or be prepared to “waste” some. There are also not quite as many choices for available widths as with regular plastic.

Please call Norm to specifically inquire about more information regarding these special coatings.

you can see more information on our covering options page

Inflator Fan Overview

An inflator fan is a very small fan which is attached to the inner layer of a double layer structure cover. Because the inflator is a squirrel cage type of fan, it can run continuously against the back pressure it has created without over heating.

The primary benefit of the process of putting air between the two layers of cover is to reduce heat loss. By having this cushion of “insulation”, the building experiences a significant reduction in condensation. The air filled pockets acts as a shock absorber therefore substantially stiffens the building in very windy locations. Covers tend to last longer since they are always tight.

The closer you are to achieving dead air space, the more these benefits can be maximized. 4”-5” of air space is optimum. Too much air space will result in air movement and reduced efficiency. When installing a double cover, both layers are on the outside of the structure but only the inside layer is pulled tight.

For all of those who are either off the grid or too far from a practical source of electricity, stay tuned for our solar powered inflator fan announcement coming very shortly

Please see #11 in our installation guide for more information https://multisheltersolutions.com/our-structure-options-coverings/installation-guide/