Like many other gardeners, in the last few years I have added structured beds to my vegetable garden that are designed to hold various covers – shade covers in summer, horticultural fleece in spring and autumn, and plastic to protect winter vegetables.
I’m still new at this, but my first season with a plastic-covered “greenhouse bed” was a phenomenal success. Spring came two months sooner for leafy greens and carrots grown under plastic, and now that autumn is around the corner, I’m wondering what to do next. For advice I turned to my friend Niki Jabbour, author of The Year-Round Veggie Gardener and more recently, Growing Under Cover. Niki gardens year-round in Halifax, Nova Scotia, a maritime climate with plenty of cold and snow. Here’s her advice for planning ahead for greenhouse beds.
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Starting with the first frost, Niki Jabbour increases winter protection for cold-tolerant vegetables
Making the Most of Row Covers and Plastic Tunnels
1. What are the best vegetables or varieties for growing under cover in a bed covered with horticultural fleece?
In late summer I use fleece over pest-prone cabbage cousins like kale, broccoli, and cabbage, because they are a great way to prevent pests from eating your crops. When the weather turns cold, I float fleece on hoops over beds over the beds filled with cool and cold season crops like lettuce, spinach, rocket, pak choi, spring onions, cabbage, and broccoli. I also use fleece in my winter polytunnel to add an extra layer of insulation to the variety of crops growing there.
2. Which vegetables or varieties thrive under plastic?
Creating a mini tunnel from plastic sheeting, or growing under cover in a plastic-covered greenhouse or polytunnel is more insulating than using fleece. I use plastic mini tunnels in late winter and early spring to create a microclimate for early planted vegetables like cabbage, broccoli, beetroot, carrots, lettuce, spinach, and celery. They give me a good head start on the growing season, with protection from animal pests. In my winter garden I use plastic covered mini hoop tunnels over crops like broccoli, kohlrabi, kale, spring onions, pak choi, endive, spinach, and winter lettuce.
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Fleece covers used inside polytunnels increase insulation for overwintering vegetables
3. Do you change from row cover to plastic as winter progresses, or use different covers on different beds?
As the autumn weather shifts to winter I toss a plastic sheet over the fleece tunnels in the garden. By that point in the season the day length has shrunk below 10 hours per day and the crops are no longer putting on much growth. The double cover offers ample protection for most cool and cold-season vegetables in my garden. We’ll continue to harvest daily from the beds until they’re empty. In late February our day length is back over 10 hours a day and I’m sowing seeds under those tunnels for fresh crops of cool season greens and spring root vegetables.
Success With Crops Under Cover
4. What is the most common mistake beginners make when growing under cover in winter?
Not watering enough. With fleece rain can pass through to the soil, but with plastic sheeting it can’t. I make sure to deep water as needed to maintain adequate soil moisture. It’s also important to vent structures like mini hoop tunnels, cold frames, and greenhouses. Heat can build up quickly, even on a day when the temperature is below freezing. I like to keep thermometers in my cold frames and polytunnel which are connected to my phone. If I see the temperature is too warm, I’ll vent the cold frame or open a window in the polytunnel.
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Moisture should be monitored closely when growing under plastic
5. Are there vegetables or varieties that are outstanding when grown in covered winter beds?
If I want to harvest lettuce from my winter cold frames, mini tunnels, or polytunnels I’ll grow ‘Salanova’ varieties or those like ‘Winter Density’ or ‘North Pole’. They’re cold season superstars! For broccoli I’ve found ‘Marathon’ to be my go-to for growing under cover in late autumn and winter harvesting. ‘Auroch’ is an excellent cold hardy spinach variety, while ‘Napoli’ carrots are incredibly sweet when dug in winter.
Thanks, Niki Jabbour. Time to get sowing!
Photos courtesy of Niki Jabbour and Storey Publishing
