The question often comes up if we can grow anything in the greenhouse during the winter, or at least start very early in spring. In zone 3 we do not grow anything in the unheated greenhouse during the winter, instead, we grow an indoor garden. In early spring, however, it is possible to grow even if the greenhouse is not heated. Here we share how to grow early peas in the winter in an unheated greenhouse under freezing winter conditions.
In this example, we grew peas, but any winter crop can be planted. We have grown lettuce, baby beets, kohlrabi, and even broccoli. Those are best started indoors (to speed up the growing) and transplanted into the greenhouse after hardening off. Read more about growing a greenhouse garden here.
How to plant early peas
It was still pretty much winter here (March 10) with 2 feet of snow on the ground and possibly more snow to come at my first attempt to grow early peas in an unheated greenhouse.
All peas are winter crops, but for growing in such cold conditions it is good to go with a special cold-resistant variety. I grew Alaska – very cold-resistant, and Tom Thumb a dwarf-growing pea, extremely cold-resistant and early.
First I sprouted the peas because it speeds up the process. I used the Biosta sprouter. It does not take long for peas to sprout, then gently plant them careful not to damage the little sprouts.
In my first attempt, I planted the sprouted peas directly into the unheated greenhouse. This year the weather forecast was extremely cold with temperatures dropping to -20C (-4F), so I did not risk planting the sprouted seeds into the unheated greenhouse but planted them into starter pots indoors instead. If starting seedlings indoors, they will germinate and grow much faster and need to be hardened off.
Still, I planted some seeds into the greenhouse to see what happens.
How to protect early peas
A single layer of greenhouse plastic keeps it in the greenhouse about 3 degrees warmer at night than the outside temperature. That is not much if we are talking about freezing temperatures usually around -12 C (10F) at that time of the year. Those little seeds needed more protection. I covered them with two extra layers of Frost Blankets. Each layer doubles the protection. The peas grew!
My trial to plant seeds at -20C worked, too. Under 3 layers of Frost Blankets, the seeds sprouted and grew. Very slowly though. Maybe the fact that our cat thought it was a great place to hang out helped too ;).
Right in time before the next load of snow, I planted out the seedlings. After a month in the seed tray, they started to flower, I could not possibly wait any longer.
The size difference between the tiny plants that were planted directly and the plants that were started indoors is huge. In the long run, though, the plants that were started directly were healthier. Facit, peas are better planted directly.
Again after transplanting, I covered everything with Frost Blankets to give more protection.
Later in the season, we have a heating and cooling system running that helps with temperature regulation. However, early in the season, with temperatures dropping below -10C 14F we do not keep water in the greenhouse, there is a danger of the system to freeze.
How to harvest early peas
Cold conditions slow down the growth of a plant. Instead of 50-55 days to maturity, it took the peas that were planted directly into the unheated greenhouse 2 months to start and 3 to be ready for harvest.
However, to eat the first peas while just starting the planting outside was so nice. Since the space in the greenhouse is needed for warm-weather crops, the peas could not stay there for too long. However, peas can be planted again right after maturing. Take some of the freshly harvested peas and plant them outdoors for another crop.
Peas are in the legume family and are nitrogen fixers. Growing them in the off-season helps to improve the soil. After harvesting the pods, cut the plants at the soil level, leaving the roots in the ground to keep the nitrogen-fixing component.
Was it worth it?
Speaking of profit – not sure. Speaking of the fun – absolutely. To see those peas grow, while outside our world was still covered in deep snow, is priceless.
Growing early peas without a greenhouse
As per usual, I sprouted some early peas at the end of March. This time however I also planted some of them directly into the garden (not greenhouse) with no protection whatsoever.
We had a cold blizzard just a month into the experiment. I did not protect these peas at all to see how far can we stretch the cold planting experiment. The seeds still germinated and grew.
The plants are healthy and productive, but they are not much ahead of the peas planted much later in spring.
In conclusion, peas can be planted very early in the greenhouse or even outside with no protection. They will start growing and producing though, whenever the conditions are right. The more protection you give, the earlier they will grow and ripen.
Have you started any peas yet? As you see peas are very hardy. If you have an unheated greenhouse grow some early peas before space will be used for heat-loving plants.