Grow in a greenhouse or tunnel the crops that the open ground cannot give you in that season: winter and early-spring greens, seedlings, and heat-loving fruiting crops such as tomatoes and peppers where summers are short or cool. Choose crops that tolerate humid air, and plan for pollination, because a closed house keeps out the wind and insects that many fruiting crops need. Do not spend protected space on bulk staples that grow well outside; use it for what only it can supply.
Crop selection for protected growing is the choice of which vegetables to put under a greenhouse or high-tunnel cover, based on what the cover adds that open ground cannot.
Protected Space Is Scarce, So Use It For What The Open Field Cannot Do
A tunnel costs frame, cover and labour. The carrier guide (Four-Season Growing & Season Extension) frames the use of cold frames and tunnels as keeping cold-hardy crops alive through winter, starting seedlings early and running a high tunnel for community food production. What the cover adds is time: earlier spring, later autumn and some winter harvest. Choose crops that exploit that.
Matching Crop To Season
| Season | Good use of protected space |
|---|---|
| Autumn to winter | Hardy greens, mâche, claytonia, spinach, kale for harvest-only picking |
| Late winter to spring | Seedlings for transplanting, early salad, early roots |
| Summer | Heat-loving fruiting crops (tomato, pepper, cucumber) in cool or short summers |
| Autumn | Finishing crops before the first hard frost |
Three Things That Change In A Closed House
- Humidity. Still, damp air favours fungal disease on tomatoes, cucumbers and some greens. Choose varieties and spacings that allow airflow, and vent.
- Pollination. Tomatoes self-pollinate but set better with air movement or vibration. Cucumbers and squash that need insects will not set fruit in a sealed house; keep doors open in the day or hand-pollinate.
- Pests. Aphids and whitefly can build up in warm, sheltered air without natural enemies.
What You Need
- A list of the crops and the season each will occupy the house.
- Space per plant and trellis for climbing crops.
- A way to water without wetting the leaves (Drip Irrigation).
Method
Step 1: List what you need from the house (winter greens, early seedlings, summer fruit).
Step 2: Match crops to the temperatures you have measured, inside at dawn and mid-afternoon (Cold Frames & Low Tunnels).
Step 3: Plan the year, with a crop in each season so the house is never idle and never overloaded.
Step 4: Rotate or replace the soil as disease builds up; a house cannot be left fallow in the open the way a field can.
Common Mistakes
- Using protected space for wheat or maize — wind-pollinated cereals need space and wind, and the same area gives far more food as an outdoor field.
- Planting a summer fruit crop in a sealed house — heat and no pollinators.
- Growing the same family in the house year after year — disease builds up.
What’s Next
- Learn next: Winter Gardening Techniques — the winter job of the house
- Combine with: Succession Planting — keeping the house full