Preparing for a Winter Greenhouse

Posted on November 23, 2021 | Categories: Uncategorized

Row Cover, Fleece and Heaters will help your winter greenhouse


It dipped well below freezing last night and the grass was crunchy crispy as we took our dog out for her walk this morning. It is not just cold.  It is putting a coat on your dog and heating your winter greenhouse kind of cold. And if you don’t want to heat your whole greenhouse, you have options this fall. Simply separate plants into different areas according to the amount of frost they can tolerate.




Most houseplants, banana trees, tropical orchids, a coffee tree I started from seed in 2019 and African violets – are tropical plants. They barely survive a whiff of chill before leaves blacken, edges crisp and plants die. Even at temperatures well above freezing, if you can’t supply summer heat in your greenhouse, I suggest moving your tropical plants out of your greenhouse and into your plus 20 C (68 F) house as soon as temperatures dip in your area.




In my greenhouse I have a navel orange, a mandarin orange and a grapefruit. These are all classed as sweet citrus and need a bit more heat than sour citrus. Last year I built a little wood frame, covered it with floating row  cover and, like the coat on my dog, this approach sheltered the semi-tropical plants inside my greenhouse within my greenhouse.

Helpful Husband sets up a fabric shelter inside my greenhouse

I plugged in a small heater set to turn on when frost is detected and placed it under the fabric cover. My sweet citrus successfully came through the winter and have almost doubled in size this summer. I am expecting my first two grapefruits in February!


Another semi-tropical is my blue banana, which tolerate colder temperatures than most bananas. I would have to kill this plant to know it’s absolute frost tolerance but I’ve been told it is the hardiest banana available so I will tuck it under cover with my oranges and grapefruit.


My Meyer lemons and Bears lime can take cold down to minus 7 C  (20 F) before the leaves die so I have been overwintering them with just old-school Christmas lights and a fabric wrap inside my greenhouse. The lights are plugged into a thermostat and as the temperature dips to zero the lights come on. Last year I had 150 lemons on one six-year-old tree.

winter greenhouse

Like grapefruit, Mandarin oranges need extra protection and will be covered over winter

Temperate Plants


Some plants easily handle a chill. A friend gave me a flower this spring that survived last night’s heavy frost and is still standing and happy outdoors even with white-frost dusting the leaves this morning. This Pelargonium, also called Ivy Geranium, has the prettiest burgundy bloom so I promised to take cuttings so it will live another year.


I will cut 15-20 cm-long  (6-8 inches) stems soon, dipping the ends into rooting hormone, and plunging the cut, dipped pieces into moist peat-lite soil. I will watering the soil and tie a plastic bag around the pot to keep the humidity high. The wrapped pot will be placed on top of my heat mat in the greenhouse because bottom heat pushes the baby roots to grow. If temperatures drop below zero inside my greenhouse, I will add a layer of Agribon-50 over the pots of cuttings on top of the heat mat.

Other temperate plants, like Echeveria, will stay alive all winter, even outside, in temperatures above minus 10 C (14 F.) But they prefer a space in the greenhouse where rain and snow will not settle on them and freeze between the leaves. If you are in a -30 C  (- 22F) kind of climate, skip covering temperate plants and bring them into a partially heated, attached garage with a window.


Hardy Plants


Most hardy plants such as arugula, kale, cauliflower or spinach can take a little or a lot of frost as long as the soil is somewhat moist. Completely dry soil stresses plants, so give it a good soak before you cover your hardy winter vegetables with  floating row cover for winter. Because light levels will be lower in winter than summer, hardy plants won’t grow a lot at least until day lengths are over 10 hours, so anything you eat will not regrow this winter. In my 49 degree latitude growth resumes at about mid-February.


Different Ways to Heat


For more ways to heat your home greenhouse check out the Online Accessories shop and consider buying a heater to keep part or all of your greenhouse warm this winter. If you want to simplify the system and keep just a portion of the  space warm, use a thermostat to turn the heater on in your inside greenhouse or covered area when the temperatures dip to the danger zone.


Keeping the air moving will also prevent cold frosty air pockets. Installing a fan and keep it running 24/7 is usually the best way to move the air around.  See Both the Horizontal Airflow and the Caframo Chinook Greenhouse fans here: https://www.bcgreenhouses.com/shop/?product-page=1.)


P.S. Don’t forget to keep track of everything you do this fall and winter so you can learn from your own mistakes and greenhouse activities. The Three-Year Gardener’s Gratitude Journal is also available in the shop so check it out.




For more great tips from Donna, visit www.donnabalzer.com.

You can also read Donna’s gardening books: No Guff Vegetable Gardening with Steven Biggs and her just released Gardener’s Gratitude Journal:  Part Diary, Part Personal Growing Guide.