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!

Growing Over Winter in a Greenhouse

There are quite a few ways to make a greenhouse more heat efficient to make it feasible to grow either through the winter or for a large part of it.

The first thing to determine is what crop(s) you wish to grow since a number of plant varieties would be considered cold weather crops. The heat requirement would be considerably less.

Since the majority of heat loss is through the roof, the most common method of making a greenhouse more heat efficient is by adding a layer of plastic to the outside. With the benefit of a small blower there is an air pocket created. The closer that this air pocket is to “dead air” the less heat transfer that there would be. 10 to 15 cm is considered the ideal gap. When there is more then 15cm there will start to be movement of air and greater heat transfer. It is impossible to have a perfectly uniform space because of the way the plastic goes over the ridge and is fastened around the edges.

It is important not to have any holes in the plastic. The resulting air loss with a hole would result in air movement and less heat efficiency.

It is often thought that a lower greenhouse is easier to heat since there is less surface area to lose heat. The reality is that the bigger air volume of a taller greenhouse is less likely to have the temperature fluctuate.

To make a structure more heat efficient, the north wall could be insulated. Care has to be exercised in insulating ends since it is important not to create extra shading. Insulation can be put flat on the ground around the structure as a way of slowing down the cold radiating into the structure.

Another trick that some people have used effectively to reduce heat requirements is to make small tunnels over the beds of vegetables. This works well for the night time. It is important to have this cover removed in the day time to maximize the value of the sunlight.

If your intention is to only use part of a larger structure through the winter, it is wise to hand a curtain for the length of the ridge and then only use the south facing side. This maximizes the benefit of the sun and minimizes the effect of the cold wind.

With a little creativity it is easy to get benefits from the greenhouse even in the winter.

Tips for How to Install a Cover and Wirelock & Growing Over Winter – Coffee Time with Norm ep.1

In the first session of Coffee Time with Norm, Norm answers Nathan Morrison’s question from Maple Grove Nursery and shares tips for installing a cover as well as growing in a greenhouse over winter

1:40 where is the end plastic attached to the end hoop?
Is it the same wirelock channel that I use for the top cover?
If so, how do I go about attaching the bottom of end wall plastic section where the roll up sides are located? (as there won’t be any wire lock down the bottom)
3:00 Norm discusses tips for installing the cover more efficiently on a greenhouse
22:40 Norm discusses growing in a greenhouse over winter and key things to keep in mind and plan for
37:00 We thank you for joining us and invite you to stay tuned for a special announcement about Self Sustainability and Our Greenhouses, coming soon!

The YouTube video mentioned in the video can be found here:
YouTube video “installing multiple covers into one wireless channel”

The article mentioned about being in a windy area can be found here:
https://multisheltersolutions.com/2020/02/28/youre-in-a-windy-area-we-can-help/
Subscribe to our website multisheltersolutions.com to be notified when the full article about Growing Over Winter goes live!

We created Coffee Time with Norm as a way to connect to everyone, regardless of which coast you live on. We aren’t able to attend trade shows this year, so this is our way of still being able to touch base face to face with customers, new and old. It will be a weekly feature, every Wednesday at 9am EST, with recordings posted on social media afterward for anyone who can’t attend live. Please send your questions to multisheltersales@gmail.com and we will address them on the next zoom call.

Please note this is a time for connection, brainstorming solutions to your challenges, learning some information about structures and other questions. If you have a question about an order, or would like a quote, please contact the office separately and we would be happy to help you.

We are excited to have you join us for this new event and we look forward to your questions!