Growing bell peppers in a greenhouse and their beneficial properties

Biological requirements and microclimate in the greenhouse

Sweet pepper is one of the most valuable vegetable crops due to its content of physiologically active substances. Consuming just 40–50 g of fruits fully covers the daily human requirement for vitamins C and P. These substances strengthen blood vessels, lower cholesterol levels, and have an anti-sclerotic effect. Furthermore, the aromatic compounds of peppers stimulate the production of endorphins, which helps to cope with stress and restore energy.

The pepper is a native of the tropics, extremely demanding of heat, humidity levels, and soil fertility. Its root system is taproot-based, branching, but grows shallowly — in a layer up to 40 cm. To obtain high yields, the crop requires light, loamy, well-fertilized soils with neutral acidity.

• Optimal daytime temperature — 25–28 °C
• Minimum nighttime temperature — 16 °C
• Growth cessation — 13 °C
• Root depth — up to 40 cm
• Daily fruit allowance for humans — 40–50 g

The irrigation and ventilation regime requires special control in the greenhouse. A lack of moisture leads to fruit set shedding, deformation, and small fruit size. At the same time, peppers do not tolerate waterlogging: the root system begins to rot rapidly, and the plant wilts.

Selection of cultivars and hybrids for protected ground

Under protected ground conditions, peppers are grown in winter glass greenhouses, as well as in heated and unheated film greenhouses. The bush shape and plant height depend on the earliness of the cultivar. The fruiting period for vigorous hybrids can last up to 7 months, while for dwarf forms it is limited to 30 days.

The time from seedling emergence to technical maturity in the greenhouse ranges from 110 days for early cultivars to 140 days or more for late ones. The lower part of the stem becomes woody over time. Each shoot ends in the formation of flowers and 1–2 fruits, while continuation shoots develop from the axils of lower-lying leaves.

To plan plantings and evaluate potential yield, use the characteristics of cultivars and hybrids presented in the table.

Cultivar / Hybrid	Ripening period and growth characteristics	Fruit characteristics	Yield, kg/m²
Solnechny	Early-ripening, tall	Light green, conical, weight 100 g	7–10
Vatag	Mid-ripening, medium-sized	Cuboid, dark red, wall thickness 6–8 mm	14–15
Dobirny	Mid-ripening, medium-sized	Cuboid, red, weight 160 g, wall thickness 5–7 mm	13
Druzhok, Pioner, Nadiya	Early-ripening, short, cold-hardy	For open and protected ground	—
Podarok Moldovy	Short	For film greenhouses and temporary covers	—
Hybrids from "Gavrish" breeding (Parizh, Alenushka, Svetlyachok, Nochka, Sirenevy Tuman, Shokoladka)	For film greenhouses	Weight 90–140 g, varied coloring (red, light yellow, yellow-orange, purple, bright lilac, brown)	5–7
Hybrids from "Mapul" breeding (Avangard, Boiman, Bourgeois, Velmozha, Grenader, Goodwin, Maestro, Mercury, Persona)	Vigorous, for winter complexes and spring heated greenhouses	Large, weight 250–650 g, long fruiting period	up to 17

Agricultural technology and bush formation in greenhouses

To obtain a high yield of sweet peppers in protected ground, it is important to maintain the temperature regime of the soil and air, as well as correctly choose the planting density. In unheated greenhouses, planting begins only after the soil temperature rises to at least 15 °C. For spring film greenhouses, medium-sized, early-ripening cultivars and hybrids are suitable: Accord, Antikvar, Bagration, Barin, E, Country, E, Centurion, Ulybka. Their fruit weight is 150–250 g, and the yield reaches 7–12 kg/m².

The crop is effective in the second rotation after harvesting tomato transplants. When planting peppers in the third decade of May, fruiting will begin in the third decade of June, and up to 7 kg of fruit per 1 m² can be harvested by the second decade of September. Also, for film greenhouses, the Zdorovie, Agapovsky, E, and Chrysolite cultivars are recommended, and for the winter-spring rotation — Mendal, Rodnik, E, and Ruza.

• Optimal age of transplants — 60–65 days
• Soil temperature for planting — not lower than 15 °С
• Optimal soil moisture — 75–80% of field capacity
• Air humidity in the greenhouse — 60–70%
• Yield in the winter-spring cycle — 9–15 kg/m²
• Yield in the spring-summer cycle — 6–7 kg/m²

Transplants are grown in 8x8 cm pots (for winter greenhouses — 10x10 cm). By the time of planting, they should have 10–12 leaves and well-developed buds. Such plant age provides a yield increase of 1.6 kg/m² compared to 45-day-old transplants. Increasing the age of transplants to 70–75 days does not have a significant effect on yield.

The planting density of pepper is from 3 to 10 plants per 1 m² and depends on the cultivation period and the vigor of the bush:

Cultivar type and growing conditions	Planting density, plants/m²	Planting pattern, cm
Vigorous cultivars (with early planting dates)	3–10	(70 + 40) х 30 or 80 х 25
Medium-vigorous cultivars in plastic greenhouses	5–6	—
Low-growing cultivars in plastic greenhouses	10	(80 + 40) х 16

Vigorous and medium-vigorous cultivars are tied to a trellis, starting from the central stem and then moving to the lateral shoots. Low-growing cultivars are grown without tying and pruning. In the practice of some greenhouse complexes, pinching and side-shoot removal are not carried out. In other farms, bush formation is a mandatory technique.

1. Remove all lateral shoots, suckers, and leaves on the trunk up to the first branching.
2. Remove the flower in the first branching.
3. Leave two main shoots on the plant.
4. As the plant grows, leave the strongest continuation shoot at each successive branching, and pinch the weaker one back to one fruit.
5. Tie each shoot to the trellis.
6. Pinch the tops of the skeletal shoots a month and a half before the end of the crop cycle.

In unheated greenhouses, during a short crop cycle, the bush is formed into three stems. Air temperature is maintained within 24–28 °С in sunny weather, 22–24 °С on cloudy days, and at 15 °С at night. The crop is very responsive to soil warming up to 24–26 °С. Sharp temperature fluctuations, lack of heat, and overheating can cause mass shedding of reproductive organs.

The nutrition system for pepper is similar to that for tomato, however, the doses of nitrogen and potassium fertilizers are reduced by 15–25%, and the maximum salt concentration in the soil solution is lowered by 30%. The crop is very responsive to loosening the soil.

Aphids cause great damage to pepper. To combat them, in addition to chemical treatments, agrotechnical methods are used: foliar top dressing with phosphorus-potassium fertilizers is performed, and greenhouse ventilation is increased to reduce the relative humidity of the air.

Growing sweet pepper under plastic covers

Under plastic covers, early pepper cultivars are used. The soil is fertilized and plants are cared for just as in greenhouses. The main feature of the technology is later transplanting. It begins when the soil temperature at 8 a.m. at a depth of 10 cm rises to 12–14 °С. Planting dates vary by zone:

• Forest-Steppe — third decade of April;
• Steppe — second decade of April;
• Polesie — first decade of May.

8–10 plants are placed per 1 m². The bush is not formed with this growing method. The covers are regularly ventilated to maintain an optimal microclimate, and in mid-June, the film is completely removed. In autumn, the plants can be covered again, which extends the fruiting period by a month compared to open-field cultivation.

Extra-early harvest technology: betting on transplant age

The first fruits of sweet pepper can be obtained in the open ground almost simultaneously with early tomatoes from under plastic covers. For this, 90–100-day-old transplants are used, which are sown in January and transplanted into the soil at the end of May, already with fruit sets. In practice, the first harvest of fruits with such planting dates is possible as early as mid-June.

The agronomic advantage of pepper over tomato lies in its high tolerance to crowding during the early stages of development. Pepper seedlings require a significantly smaller feeding area — only 8x8 cm. By comparison, an 80–90-day-old tomato plant requires a soil volume of at least 1 liter.

• Seedling age — 90–100 days
• Feeding area per seedling — 8x8 cm
• Planting time in soil — end of May
• Start of harvest — mid-June
• Fruiting period of local cultivars — more than 80 days

Characteristics of sweet pepper cultivars and hybrids

In global breeding, there are more than 200 cultivars of sweet pepper, categorized by the growing season from emergence to biological maturity. Early-maturing cultivars ripen in up to 120 days, mid-maturing — from 121 to 140 days, and late-maturing require more than 140 days. Most local early-maturing cultivars form a compact, semi-spreading bush 50–70 cm high and can support a load of 20 or more fruits per plant.

Under unfavorable growing conditions, the group of cultivars with high ecological plasticity, such as Samotsvet, Smaragd, and Miro-, performs well. In the event of a sudden cold snap or moisture deficit, these plants temporarily suspend growth, and dark purple spots may appear on the fruits. After optimizing the temperature regime and irrigation, the spots disappear, and the plants resume normal vegetation.

Cultivar / hybrid	Ripening period, days	Fruit weight, g	Wall thickness, mm	Fruit features and color
Pioner	100–120	60–70	4–5	Red, pointing upwards
Druzhok	100–120	60–70	4–5	Red, drooping
Nadiya	100–120	60–70	4–5	Red, orientation mixed. In technical maturity — cream-colored
Golubok	100–120	60–70	4–5	In technical maturity — cream-colored
Svetlyachok	100–120	small	4–5	Yellow-orange, cone-shaped, for stuffing
Snegir	100–120	60–70	4–5	The thickest-walled and most productive in its group
Poltavskiy	135–140	60–70	4–5	In technical maturity — green
Zlagoda E (hybrid)	mid-early	80–100	thick	Cone-shaped, salad green in tech. maturity, red in biol. maturity. In the register since 2004
Valyusha	mid-early	100–125	thick	Cone-shaped or prism-shaped, from pale yellow to red. Yield up to 4 kg/m²
California Wonder	late-maturing (September)	200–300	8–9	Cubic, dark green / dark red. Fruits are tightly pressed to the stem
Krupnyy Krasnyy	mid-early	200–400	thick	Large-fruited, ripens earlier than California Wonder
Zheltyy Gigant	mid-early	200–400	thick	Large-fruited, ripens earlier than California Wonder

Choice of predecessors, soil preparation, and planting of pepper

To obtain an ultra-early harvest, the focus is on early-maturing cultivars. The Hungarian cultivar Shoroksary and the Dutch cultivar Venti have proven to be excellent. When sowing for transplants in February and planting blooming plants with fruit set in late May, the first green fruits can be harvested as early as mid-June. The fruits of the Shoroksary cultivar in technical maturity are light green, in biological maturity — red-orange, reach a weight of 250–450 g, and are distinguished by very delicate skin.

The best predecessors for pepper are perennial grasses, cucurbit crops, carrots, and onions. The soil should be fertile, well-drained, and have a neutral pH.

• Optimal soil acidity — pH 6–6.6
• Minimum soil temperature for planting — 15–16 °C
• Depth of stem embedding — no more than 2–3 cm
• Isolation from hot cultivars — at least 200 m

When preparing the site, it is important to avoid excess nitrogen. The application of fresh manure causes "over-vegetation" of the plants — active growth of green mass to the detriment of fruit formation, and also increases the risk of rot and aphid reproduction in greenhouses. During autumn tilling, 5–10 kg of humus, 60 g of superphosphate, and 25 g of potash fertilizers are applied per 1 m².

In regions with a favorable climate, a direct-seeding method for early cultivars is permissible. The seed is sown in the third decade of April directly into the soil under protective caps made of plastic bottles or paper bags. The rate of seedling emergence directly depends on soil temperature: at 13–15 °C, emergence occurs in 20–25 days, and at 20–25 °C — as early as the 7th–10th day.

When planting transplants into open soil in the third ten-day period of May, the layout scheme is chosen based on the plant habit:

Cultivar group	Row spacing, cm	Distance within a row, cm
Medium-sized, medium-fruited (Druzhok type)	70	15–20
Large-fruited (depending on bush vigor)	70	30–50

Irrigation, soil care, and fertilizer application regimen

The pepper root system recovers slowly; therefore, it is important to minimize stress for the plants during transplanting. Planting is carried out according to the following algorithm:

1. One or two handfuls of humus and a teaspoon of nitroammophoska are added to the planting hole, followed by abundant irrigation.
2. The nursery plant is placed into the hole, maintaining the same planting depth as during the seedling period, or by burying the stem no more than 2–3 cm deep.
3. The work is carried out in cloudy weather or in the evening, and initially, the transplants are shaded with available materials.
4. From overgrown transplants, the first fruits are harvested as soon as possible so that the plant forms a normal bush with a good assimilation surface.

Due to the superficial root arrangement, soil loosening is carried out extremely carefully so as not to damage the root system and fragile stems. If mulch is not used, loosening is mandatory after each irrigation. In the second half of the growing season, it is recommended to earth up the plants — this protects the roots from exposure and increases the stability of the bush. In hot weather, refreshing irrigation is carried out to prevent the shedding of buds and fruit set.

A high concentration of salts in the soil solution harms the crop, so top dressing is carried out fractionally. Throughout the season, pepper is fertilized 3–4 times, alternating organic matter and mineral mixtures. To prepare a liquid mineral top dressing, add the following to 10 l of water:

• Ammonium nitrate — 15–20 g;
• Potash fertilizers — 15–20 g;
• Superphosphate — 40–60 g.

The application rate of the working solution is 0.5–1 l per plant, depending on its age.