GardenLine | Vegetables | Peppers in the Greenhouse

The cold wind has all but blown away the memory of the taste of summer's vine-ripened vegetables and fruits. But with a greenhouse, crops like peppers and tomatoes can be grown year- round.

If you have a small greenhouse, consider small-scale production of petters or tomatoes.

While soil is fine in the garden, it is not well suited as growing medium in a greenhouse: it does not allow adequate aeration and usually harbours disease. Most growers use a soilless mix, which had the advantage of being lightweight and disease-free. But because soilless media do not provide or store nutrients, these must be supplied as either a slow-release fertilizer or, more commonly, in the water applied to the greenhouse plants.

Although seed can be sown in late summer for early winter production, fruit produced during months of low light conditions are often small or deformed. Supplemental light can be used to improve fruit quality during months with limited light, but this adds to the cost of production. See the sidebar below for a more cost-efficient production schedule which does not require artificial lighting and involves only on pepper crop per year.

A daily application of fertilizer solution is recommended. Small- scale growers should apply 20--20--20 with macronutrients according to label directions. Larger operation should apply fertilizer at the rate of 225 ppm nitrogen, 40 ppm phosphorus, 350 ppm potassium, 175 ppm calcium and 40 ppm magnesium.

The climate within the greenhouse will influence the quality of the fruit. A relative humidity of 75% is ideal. Lower humidity will decrease growth and stimulate flower production, creating a large fruit load at the expense of a strong , healthy plant. Extremely high humidity will encourage disease.

Different temperature are required of the plant's life cycle. For optimum germination, the media temperature should be 26°C. After germination, this should be reduced to 24°C. Once the crop is transplanted into the greenhouse, the root zone or media temperature should be reduced to 21°C, with a daytime air temperature of 23°C and a nighttime air temperature of 19°C to 20°C. To stimulate fruit set. maintain an air temperature of 16°C at night and 23°C during the day.

Light conditions greatly influence the length of time it takes seedlings to reach the transplanting stage. Seedlings transplanted into the greenhouse from January 10 to April 15 need to be 85 days old, whereas seedlings sown after April 15 are typically only 50 days old when transplanted.

Once transplanted, and in order to support fruit development, plants must build a strong root system. and large leaf area. To maximize production, prune each plant to a two-stem system. The two strongest stems are selected to be fruit bearers and are attached to strings extending from the base of the plant to wires located 2.5m above the bench. These stems are permitted to branch, but all additional stems should be removed. Lateral shoots on the first 5 to 7 nodes of the plants should also be removed. Above the seventh node, simply remove the laterals to leave only one leaf/lateral.

Once the plant has four or five branches it is ready for pepper production. To encourage fruit set. gradually decrease night temperatures to 16°C over a period of three days to avoid shock. Once the fruit has set,. raise the night temperature to 19°C and the day temper to 22°C or 23°C to encourage fruit growth. A maximum of two peppers per tem is recommended for the fist fruit set. A larger fist set will decrease future yields. After the second fruit set. The plants should be strong enough to handle all fruit that is set. In full production (approximately six months after planting), the maximum load is five peppers per stem, To avoid "flushing" (a period of heavy fruit followed by a period of light fruit set), do not increase the temperature after the fist fruit set. A flushing pattern can also be avoided if all stages of fruit are present on the plant during production.

Harvest pepers with a sharp knife. cutting the junction between the fruit stem and the main stem. Fruit shoudl be picked when theya re 85% to 90% coloured since additional ripening will occur off the vine.

Cultivars for greenhouse production:

red: `Cubico,' `Mazurka,' `Delphin'

green to orange: `Eagle,' `Arianne'

green to yellow: `Kelvin,' `Goldflame,' `Rarantella,' `Luteus'

purple: `Violetta'

© 1996 Jackie Bantle

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Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.