I get lots of folk asking about building domes to grow food year round so I thought that Iíd put a page together with some facts and information about the challenges of growing year round. First we need to establish what we mean by growing, we can crop in winter without a greenhouse of any kind and we can overwinter tender plants in a greenhouse that doesnít freeze, neither of these provide the right conditions for plants to actively grow in winter.
It doesnít matter what system you use, growing in the ground, hydroponics or aquaponics if you donít have plenty of sunlight plants will not grow! On a sunny day in January you will get about thirty times less sunlight than a sunny day in July, this may seem to be an underestimation but the sun is much lower in the sky and the days are much shorter, trust me I have tested solar panels, solar hot water systems, anything that makes use of solar energy produces hardly anything in the winter. Because plants use the suns energy for photosynthesis no sunshine means no growing, even if you have a nice warm greenhouse your plants wonít grow without plenty of sunlight. Sure some winter kale will put on a little greenery but you wonít get any growth that will provide real food energy.
Is it possible?
Sure growing food in the winter is possible in the countries around the equator, the southern hemisphere is in summer when the northern hemisphere is in winter so we can send food back and forth as the winters interchange, this is how we currently do things but it does have a high energy footprint, this is the reason why most people want to try and grow food locally year round. To grow food in the winter we need to provide the same growing conditions as we have in summer or at least springtime this is where we hit some problems. We need to provide at least ten hours of strong sunlight and a temperature of around twenty degrees centigrade, the good news is if we have a bunch of grow lights and a well insulated greenhouse we donít need to provide any extra heat because the grow lights give off heat as well as light. The bad news is running those grow lamps is going to cost you in energy, about 6 Kwh per square meter per day, I make that roughly £84 per square meter over a typical winter, way more than the value of any crop or even the energy to transport food from a warm country.
A better idea would be to have a greenhouse that makes the most efficient use of the solar radiation available at a given time of year rather than trying to make our own summer inside a greenhouse, With this in mind I designed a theoretical super efficient greenhouse that doesnít require any energy to run but provides the best possible growing conditions using only the available energy from a weak low lying sun and ground source heat below the greenhouse.
In this video I talk a bit about some of the challenges of growing in winter and look at the potential of using a water butt inside the dome as a passive heat source.