Optimize Your Greenhouse for Year-Round Food Production: Tips & Tricks

Optimizing Your Greenhouse this Winter by Growing Food Year-Round

In my region an atmospheric river flooded out roads, rails and farms. This probably seems pretty minor compared to areas affected by cyclones and hurricanes but one thing is certain: there has never been a better time to own a greenhouse.

Growing Food in My Greenhouse:

I am the lucky owner of two BC Cross Country greenhouses. I overwinter tender potted plants like lemons, blue bananas and decorative Echeveria in my smaller 8’ x 12’ greenhouse space where I keep the air temperature at or above 5 C or 41 F.

My larger 16 x 20 greenhouse has soil beds built into the ground. The beds are 14’ inches high and the ground beneath the beds go into the native soil below. I plant seasonal food crops, seasonal flowers and herbs in this big greenhouse. I seed directly into the soil or transplant from pots I grow on my giant 48” x 20” heat mat in the greenhouse. I keep the temperatures in the greenhouse above freezing so the water lines and soil don’t freeze.

Zinnias in my fall garden were started on a heat mat in April

Both greenhouses are outfitted with heaters attached to thermostats. I can adjust the thermostats so the heaters prevent freezing or more actively heat the space. A fan runs continuously to keep air moving and prevent mold and mildew and continue successfully growing food.

My main goal is to keep the frost at bay because in winter I grow food crops that takes a chill and keeps on growing like kale, green onions, lettuce, leeks, peas and parsley. Other frost tolerant crops that can be grown in a cool greenhouse include celeriac, carrots, beets, mustard greens, parsnips, spinach and arugula. Tropical plants, like tomatoes, peppers, zucchini, cucumbers and basil; are removed on or before October to make way for winter crops.

Tomatoes are started indoors before moving into pots and finally into the greenhouse.

Small lemon trees are overwintered in my smaller cool greenhouse.

Greenhouse Soil:

The growing space in my greenhouse is smaller than in my outdoor garden and the soil is being used constantly, all year-round. Over time, soil in permanent beds must be enhanced or fed.

Greenhouse soil becomes deficient in specific micro-nutrients like Boron or macro-nutrients like nitrogen. A late-season boron deficiency in carrots causes cracking while in cauliflower it triggers a brown hollow centre. A nitrogen deficiency means plants will be smaller with lower leaves that yellow. I test soil occasionally but meanwhile use general purpose Biofert organic fertilizer and extra calcium to keep the soils healthy.

The Role of Micro-Organisms:

Micro-organisms supply and deliver mineral nutrients to plants. All green growth makes sugars to energize microbes. To thrive long-term, microbes need a constant source of plant sugars (carbohydrates) so they can keep on working. When you pull out a tomato crop and nothing replaces it, there is nothing there to feed the soil microbes. This is why, a year ago, I started planting fall cover crops inside my greenhouse.

Mid-simmer visit by ducks helps with bug control in my greenhouse.

Cover Crops:

Many plants, including fall rye, buckwheat and peas are used as cover crops. It is all good but a cover crop like field peas is better than most. Like other green plants, peas make sugars and share them with the soil’s microbes. Like other plants, the tops and roots of peas add to soil organic matter when they die. Unlike other plants, a cover crop of peas or other legumes, team up with bacteria and manufacture some of their own nitrogen with the cooperation of specialized bacteria.

Arugula seeded in greenhouse soil November 5th after peppers are pulled.

I use about 25% of my greenhouse beds for peas or other cover crops over winter.

Beneficial Bugs

Growing better soil involves planting a cover crop in the fall but also adding soil organisms such as beneficial bugs. Ever wonder why spider mites are more of a problem on a single houseplant than in a huge greenhouse? A topdressing of compost or worm castings can add beneficial organisms like Stratiolaelaps scimitus (formerly Hypoaspis miles) to your greenhouse soil and in the winter these good bugs eat the resting mites snuggled up in your soil or around your pipes and paths. These beneficial insects are also available from suppliers https://naturalinsectcontrol.com in Canada or https://www.arbico-organics.com/ in the USA.

Scheduling Crops for Success

Obviously taking time to rotate crops, plant cover crops and keeping things green and growing makes year-round growing complicated. This is a 4-D puzzle for new greenhouse growers who need to calculate how many dinner parties they’ll host or how many  pizzas with arugula they will serve during each season. Count how many beets you will roast or celeriac soups you will prepare over the winter and measure out the green onions, not in bunches like store-bought scallions, but as individuals for salads. If this is all too much just keep track of what you buy for a year or even a winter season and start by growing to meet your needs.

Adding Grow Lights

To streamline my operation and make my greenhouse more efficient I employ a set of grow lights inside my home. This way I can start spinach indoors in August, plant it in the greenhouse after my tomatoes are removed in October, and start eating it in February.

I hang onto tomatoes as long as possible but pick most of them by November when light levels drop.

I start seeds of onions and leeks indoors in February and move them onto shelves in my still-cool greenhouse in March. Then I start tomatoes and peppers under lights indoors. By mid to late April, I’ll raise the greenhouse heat, finish harvesting my winter crops and start moving summer crops from my grow-lights into my greenhouse. Then I will start herbs and flowers indoors in flats that can be transplanted and moved to my greenhouse shelves in mid-late April.

Eat Well Despite the Weather

I had a dinner party for friends during the big rains and everyone was amazed at the food served, mostly picked from my garden and greenhouse. If I was depending on growing everything outside there would be trouble and twelve people would have gone home hungry. The greenhouse is the anchor point that allows me to grow food year-round.

And yes, we had crazy weather this fall but we are not the first region with freak storms. Thankfully our greenhouse and growing food takes the edge off and gives us some breathing room. I wouldn’t be without it.