The Cullens: Greenhouses for when the snowbirds don’t fly  

Mark Cullen's greenhouse is practical – a cedar frame kit with cantilevered windows for ventilation. In the spring, a small electric heater keeps tender seedlings frost-free. Supplied

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There is one migration we do not expect this winter – that of the snowbirds, or Canadians who are known to head south for the cold winter months. Sure, some will suffer the border-crossings and quarantines, but most that we know personally seem to be staying close to home this winter.

We picture stranded snowbirds looking longingly upon their snowy backyards, imagining the warmth of the Florida sun upon their skin.

These fantasies lead us to architecture – specifically, greenhouses.

Much of our greenhouse inspiration comes from another far-off and out-of-reach destination, the United Kingdom. From the humble allotment glasshouse, to the orangeries of Kew Gardens and Kensington Palace, the British have a long history of employing architecture for the joys of year-round gardening and sunny solace.

If you find yourself imagining this sunny escape in your yard, here are a few things to consider:

  • Use: Will this serve as a tearoom, or do you plan on maximizing your winter kale production? While we are happy sipping our tea under a large poly grow tunnel, we can appreciate that you might have pictured something more elegant. Consider whether your greenhouse is simply for season extension, like a large cold frame, or if you plan to heat it through the winter. Which leads us to …

 

  • Cost: The range is huge – starting with under $500 DIY builds, the sky is the limit as far as what you can spend. Here are some guidelines:

– At the luxury end of the range, expect to spend around $350-$500/square foot for a serviced, aluminum frame greenhouse with some architectural flair. Mark’s sister Nora recently built such a unit, which employed a prefab aluminum greenhouse structure atop a brick foundation, which looks quite slick. Throughout the winter, it houses her tropical plants such as bougainvillea and Kimberly ferns, which create an oasis around her small lap pool. As an alternative to a Florida home or cottage, it is quite economical – never mind the inconvenience and expense saved by not travelling.

– Mark’s greenhouse is slightly more practical – a cedar frame kit with cantilevered windows for ventilation. In the spring, a small electric heater keeps tender seedlings frost-free.

– For the even more practically minded, there is plenty of creative opportunity to reuse materials to create a basic structure covered with poly film which is only going to run you about a $0.15/square foot. Commercial nursery farms often use poly greenhouses – referred to as “poly tunnels”. The “ends” of the greenhouse cost the same whether it is 30 feet or 100 feet – so stretch it as far as you can!

 

  • Ventilation: Insects and fungal diseases thrive in the sort of warm, humid environments you find in a greenhouse. Higher end builds and kits include ventilating windows built into the design.  DIY’ers ought to keep this in mind. Locate your greenhouse crosswind in a breezy area to minimize the number of fans required to keep air circulating.

 

  • Heat: At the historic Lost Gardens of Heligan in Cornwall, England the 200-year-old, refurbished “Pineapple House” is heated with rotting compost which provides pineapples year-round. Another low-tech, sustainable solution is to place a large “thermal mass” such as a barrel of water on the floor of a heated greenhouse to absorb solar heat during the day and radiate the heat at night.

If you are planning on heating right through the depths of winter, however, a gas furnace is likely your best bet as electric heating can get expensive quickly.

Whether you’re just getting a little more out of our waning summer, or you decide to power right through the winter in your sunny oasis, a greenhouse can be a great place to relax or indulge your gardening passion. A sanctuary for snowbirds.

 

Mark Cullen is an expert gardener, author, broadcaster, tree advocate and a Member of the Order of Canada. His son Ben is a fourth-generation urban gardener and graduate of the University of Guelph and Dalhousie University in Halifax. Follow them at markcullen.com, @markcullengardening, and on Facebook.

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