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Andrew's Four Season Greenhouse

Updated: Aug 4, 2021

It’s cold in Atlantic Canada. So very cold, for so very long! Our last frost date is usually somewhere towards the end of May, so our growing season here is short. Andrew and Anna Mathis really wanted to extend their growing season so Andrew designed and built a four season greenhouse on their homestead in rural New Brunswick.

They were harvesting tomatoes from it last January, while some New Brunswick-ers were possibly getting frostbite carrying their groceries home. Frostbite and growing tomatoes aren’t words that usually go together so how did the Mathis' do it? Andrew, a PhD student at the University of New Brunswick, put his mechanical engineering skills to good use and he came up with an innovative design that captured and stored the sun’s heat, and released the stored heat on cold nights.

Check out our article on Andrew’s design and process on our blog soon!

It’s been three years since they built their solar passive greenhouse and they are still experimenting with the space to figure out what to grow in it. They have a hoop house on their homestead as well, and all the plants really thrive there in the summer months, while the solar passive greenhouse is a much more expensive space per square foot, so they know it makes sense for them to grow crops that are more valuable there. Right now they are using the greenhouse as a tree nursery. They have 5 black locust trees, 10 honey locust trees, avocado plants that will be sold as houseplants in the fall and a lime tree that has already survived two winters there.

Other crops he’s had success with in the greenhouse are ground cherries, perpetual spinach and arugula. Andrew has temperature sensors that measure the outdoor temperature and the indoor temperature and it can be -10 degrees outside and +20 degrees inside the greenhouse on a sunny day. Overnight the temperature inside the greenhouse is able to stay above freezing, except on consecutively cloudy days. Andrew says he has to seal the vents still and he expects the performance to increase once that’s done. He built a similar greenhouse at The Ville in Marysville, that was well sealed and it maintained a temperature of 5 degrees in the winter with no supplemental heat. In 5 degrees you can grow almost anything.

One issue they’ve faced has been successful pollination. Crops are isolated from pollinators in the greenhouse, so the crops they grow in there either need to be hand pollinated or be self pollinating. Tomatoes do well there because they don’t need much pollination. He’s really excited about growing figs in the greenhouse this year because they don’t need to be pollinated. Figs can’t be grown outside in Atlantic Canada, and they’d need lights to be grown inside. He is also going to grow dwarf bananas. A lot of plants really slow down their growth over the winter but they can still be harvested year round. It’s even possible to start plants late in the fall and save plants from other gardens that would normally die, by transplanting them into the greenhouse over the colder months. As the deepest, darkest part of winter sets in, some plants, such as peppers and tomatoes, have been cut right off to ground level and then have grown back up from their roots in the spring.

What Andrew did can be easily replicated, and we will go into more detail on how you can build your own four-season greenhouse in our upcoming articles.

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