How to Grow Peppers in a Greenhouse

Greenhouse peppers outperform outdoor peppers in every measurable way: earlier harvests, higher yields, longer seasons, and fewer pest problems. The controlled environment eliminates the two factors that limit outdoor pepper production — cool nights that slow growth and unpredictable rainfall that promotes disease. Whether you grow sweet bells, hot habaneros, or specialty varieties for market, a greenhouse gives you the conditions peppers evolved to thrive in.

Temperature Requirements

Peppers are tropical plants that stop growing below 55°F and suffer cellular damage below 40°F. Optimal daytime temperature is 75 to 85°F with nighttime lows of 65 to 70°F. The day-night differential triggers fruit set — consistent temperatures without a 10 to 15 degree nighttime drop often produce vigorous plants with few fruit. A greenhouse with automatic vents and a backup heater set to 60°F provides this cycle reliably from spring through late fall.

Hot pepper varieties (habanero, ghost pepper, Carolina Reaper) prefer even warmer conditions: 80 to 90°F days and 70 to 75°F nights. These varieties benefit from the hottest spot in the greenhouse — typically the south-facing bench closest to the glazing. Cool-weather slumps that stall outdoor hot peppers are eliminated under glass.

Container Selection and Soil

Most greenhouse peppers grow in 3 to 5 gallon containers (sweet bells, jalapeños) or 5 to 7 gallon containers (habaneros, larger plants). Use a well-draining potting mix with perlite — peppers are susceptible to root rot in waterlogged media. Fabric grow bags work well for peppers because the air-pruning effect creates dense root systems that support heavy fruit loads.

Light and Spacing

Peppers need a DLI of 15 to 20 mol/m²/d for optimal fruit production. In most greenhouses, natural light meets this requirement from April through September. During spring starts and fall extension, supplemental LED lighting (200 to 300 µmol/m²/s at canopy height for 8 to 10 hours) bridges the gap. Space plants 18 to 24 inches apart in all directions — peppers need air circulation around the foliage to prevent fungal disease, and crowded plants compete for light, producing fewer, smaller fruit.

Pruning and Support

Pinch the growing tip when seedlings reach 8 to 10 inches tall. This forces branching and creates a bushier plant that supports more fruit. Remove the first few flowers to redirect energy into vegetative growth — a larger plant produces more fruit over the season than one that sets fruit while still small. Once the plant has 8 to 10 branches, allow fruit to set freely.

Support heavy-fruiting pepper plants with Y-stakes, small cages, or string tied to an overhead wire. A fully loaded bell pepper plant can carry 3 to 5 pounds of fruit — enough to snap unsupported branches. Hot pepper plants with smaller fruit rarely need support unless they grow very tall.

Watering, Feeding, and Common Problems

Water consistently — irregular watering causes blossom end rot (calcium uptake disruption) and flower drop. Drip irrigation on a timer provides the most consistent moisture delivery. Feed with a balanced fertilizer during vegetative growth and switch to a low-nitrogen, high-potassium formula when fruit begins to set. Calcium supplementation (gypsum or calcium nitrate) prevents blossom end rot in fast-growing greenhouse plants.

Aphids and whiteflies are the primary pepper pests in greenhouses. Deploy Aphidius colemani wasps for aphid control and Encarsia formosa for whitefly. Thrips can scar fruit and transmit viruses — use Amblyseius cucumeris sachets as preventive biocontrol. Powdery mildew appears in humid, poorly ventilated greenhouses — increase air circulation and reduce overhead watering to prevent it.

Harvesting and Season Extension

Harvest sweet peppers when they reach full size and desired color — green peppers are simply immature fruit that will ripen to red, yellow, or orange if left on the plant. Fully ripe peppers have higher sugar content, more vitamin C, and better flavor but shorter shelf life. Hot peppers are harvested at maturity when they reach their final color and are firm to the touch.

A greenhouse extends the pepper season by 2 to 4 months compared to outdoor growing. Start seedlings under heat mats in February, transplant to the greenhouse in April, and harvest from June through November in most climates. In heated greenhouses maintained above 55°F, pepper plants can produce fruit into December. Overwintered plants (cut back and kept dormant at 55°F through January and February) break dormancy in spring and produce earlier and heavier first harvests than new seedlings.

End-of-season green peppers that will not ripen before frost can be harvested and ripened indoors on a sunny windowsill. They will not develop the full sweetness of vine-ripened fruit but are perfectly usable in cooking. Hot pepper varieties can be dried on the plant by withholding water in late fall — the fruit desiccates naturally on the stem, producing dried peppers ready for grinding or storage.

For growers interested in maximizing total pepper production per square foot, intercropping short and tall varieties works well in a greenhouse environment. Plant compact jalapeño or Thai chile plants between taller bell pepper plants — the shorter varieties utilize the lower light zone that the taller plants shade, and the combined planting produces more total fruit per bench foot than monocropping either variety alone. Stagger planting dates by 2 to 3 weeks to spread the harvest window and avoid overwhelming yourself with fruit all at once.