A greenhouse extends the growing season and modifies the climate, but it does not eliminate all the constraints that outdoor growers face. Light is the most significant limiting factor in Canadian greenhouses during the months from October through February, when day length drops and overcast conditions are common across most of the country. Crop planning that accounts for reduced winter light — rather than attempting to grow the same crops in the same way through all seasons — typically produces more consistent results.
Growing Media: Options and Applications
Greenhouse crops can be grown in native or amended ground soil, in raised beds, in containers, or in true soilless systems. Each approach has different capital requirements, management demands, and suitability for different crop types.
Native and Amended In-Ground Soil
Growing directly in the native soil beneath the greenhouse is the lowest-cost approach but carries the highest long-term pathogen risk. Soilborne diseases accumulate over successive seasons, particularly in crops like tomatoes and cucumbers that are grown in the same beds repeatedly. Soil solarization between crops, rotation with non-susceptible crops, and periodic deep tillage with organic matter amendment help manage this, but commercial-scale operations have largely moved away from in-ground soil for these reasons.
For home growers with a small greenhouse, amended in-ground soil works well for the first several years if rotation is practised and disease pressure is monitored. Adding quality compost, aged manure, and perlite improves drainage and aeration, both of which are critical in a covered environment where rainfall does not leach excess salts.
Raised Beds
Raised beds filled with a purpose-blended growing mix provide better drainage and temperature characteristics than native soil, and they allow more precise control of the root environment. A common greenhouse mix combines roughly equal parts of peat moss (or coco coir), perlite, and quality compost. This blend holds moisture while draining excess water freely and maintains good aeration as organic matter breaks down.
Raised beds are practical for leafy greens, herbs, and root crops. For tall fruiting crops like tomatoes and cucumbers, the bed depth should be at least 30 cm to accommodate the root system without restriction.
Soilless Growing Media
Soilless media — including peat-perlite blends, coco coir, rockwool, and various expanded clay aggregates — are used in container and trough systems across the full range of greenhouse crop types. They eliminate the pathogen risk of in-ground soil and allow precise management of pH and nutrient delivery through fertigation (fertilizer applied via the irrigation system).
Coco coir has gained popularity as a more sustainable alternative to peat moss. It is a byproduct of coconut processing and has a similar water-holding capacity to peat, with a slightly higher natural pH. It does not compress as quickly as peat over a growing season and generally holds its physical structure well.
Rockwool (mineral wool) is the standard medium in many commercial tomato and cucumber operations because it is inert, has predictable water-holding characteristics, and can be sterilized and reused for multiple seasons. It requires careful pH management — the irrigation solution pH should be adjusted to 5.5–6.0 before application to keep nutrient availability in the appropriate range.
Soilless growing requires that all plant nutrients are delivered through the irrigation water. A two-part or three-part nutrient concentrate is mixed at the required dilution rate and applied at each irrigation event. EC (electrical conductivity) of the nutrient solution is the primary indicator of total dissolved nutrient concentration; pH determines which nutrients are chemically available to plant roots. Both should be measured and adjusted regularly.
Crop Planning by Season
Year-round production in a Canadian greenhouse is best approached as a series of overlapping crop cycles timed to match seasonal light and temperature conditions. The planning framework below is broadly applicable across most Canadian climate zones, with adjustments for local conditions.
October to February: Low-Light Season
This period represents the most challenging growing conditions in most Canadian greenhouses. Day length is short, overcast weather reduces available light, and heating demand is at its highest. The crops best suited to these conditions are those with relatively low light requirements: leaf lettuce varieties, spinach, arugula, mâche (corn salad), chard, kale, and most culinary herbs.
Lettuce is particularly well-adapted to low-light greenhouse production. Varieties selected for greenhouse use — often labelled as "butterhead," "loose-leaf," or "romaine" types bred for indoor conditions — germinate quickly, grow to harvest in as little as 45 to 55 days from transplant, and tolerate the lower temperatures of a minimally heated greenhouse.
Basil is an exception among herbs: it requires warmth and reasonable light and typically produces poorly in unheated or minimally heated Canadian greenhouses through January. Parsley, cilantro, and chives are more cold-tolerant and can produce usable growth at lower light levels.
January to March: Starting Long-Season Crops
January and February are the appropriate time to start tomatoes, peppers, and cucumbers from seed if the intent is to have transplants ready for the primary growing season that begins in March or April. These crops require six to eight weeks from seed to transplant-ready seedling, and they benefit from the gradual improvement in day length and light intensity through February and March.
Supplemental lighting with LED or high-pressure sodium lamps is used in many commercial operations to extend the photoperiod during this critical seedling period. For home growers, a simple LED grow-light rack above a propagation bench can dramatically improve seedling quality during the darkest months without a significant energy investment.
March to May: Spring Transition
As day length increases through March and April, light becomes less of a limiting factor in most Canadian greenhouses. This period supports rapid growth of the warm-season crops started in January and the continuation of cool-season leafy greens and herbs. Transitioning from one to the other requires planning the timing so that the cool-season beds are cleared before fruiting crops need the space.
Radishes, peas, and early beans can be direct-seeded into cleared beds during this period. These crops tolerate the temperature fluctuations of early spring — cold nights, warm days — better than heat-loving fruiting crops.
May to September: Primary Growing Season
The late spring through early fall period is the most productive time in the Canadian greenhouse. Tomatoes, cucumbers, and peppers produce heavily when heat and light are abundant. Managing the transition from heating to ventilation-dominated climate control is the main operational challenge, along with monitoring for pest pressure that increases with warm temperatures.
Greenhouse-specific varieties of tomatoes and cucumbers are bred for the supported-culture (staking and trellising) system common in protected cultivation. Indeterminate tomato varieties are trained up twine or wire and allowed to grow several metres in height over the season. Cucumbers are similarly trained vertically and produce for an extended period when old fruits are removed promptly.
September to October: Second Cool-Season Window
As outdoor temperatures cool in September, a second round of leafy greens and herbs can be sown or transplanted to fill the beds being vacated by exhausted summer crops. This succession is often overlooked but provides productive use of the greenhouse as natural light remains reasonable through October.
Pest and Disease Management in the Greenhouse
A covered growing environment reduces some of the insect pest pressure that outdoor growers face, but it concentrates conditions that favour others. Whitefly, aphids, spider mites, and fungus gnats are among the most commonly encountered greenhouse pests in Canada. Fungal diseases — particularly botrytis grey mould and powdery mildew — are persistent risks in humid conditions.
Integrated pest management (IPM) approaches are well-established in greenhouse horticulture. Predatory insects — Encarsia wasps for whitefly, Phytoseiulus mites for spider mites — are commercially available and used as biological control agents in many small and commercial operations. Yellow sticky traps provide early detection and some level of population suppression for flying pests.
Structural sanitation between crop cycles — removing all plant debris, washing down surfaces, and allowing the greenhouse to sit empty for a brief period — reduces inoculum from the previous season and should be treated as a standard part of the production calendar rather than an optional task.
Practical References for Canadian Growers
Agriculture and Agri-Food Canada publishes technical guides on commercial greenhouse vegetable production, including variety performance and pest management protocols. The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) produces detailed production recommendations for greenhouse tomatoes, cucumbers, and peppers specific to Ontario conditions, many of which apply broadly across similar climate zones.
University extension programs at institutions including the University of British Columbia, University of Guelph, and Dalhousie University Faculty of Agriculture have produced research-based resources on protected cultivation and small-scale greenhouse production.