Regulation of the light regime when growing ornamental flower crops

Ornamental crops originate from different geographical zones; therefore, through evolution, they have adapted to different light and temperature conditions. In practical floriculture, the light regime is regulated by three key parameters: intensity (in lux), spectral composition, and duration of illumination. To obtain high-quality cut flowers and viable planting material, an agronomist must group plants according to their ecological requirements and control day length.

Classification of crops by light intensity requirements

Light-loving plants (heliophytes) physiologically cannot tolerate shading and, in natural conditions, grow in open spaces. This group includes most popular flower crops: aster, marigold, carnation, rose. They are characterized by thick leaf blades, a powerful cuticle, a developed network of veins, a large number of stomata, and high intensity of photosynthesis and respiration.

Shade-loving plants (sciophytes) are adapted to constant shading and feel best under a forest canopy. This includes ferns, aspidistra, and other plants of the lower layers of tropics and subtropics. Their leaves are usually thin, consist of large cells with large chloroplasts, and contain a lot of chlorophyll.

Shade-tolerant plants possess a broad ecological amplitude in relation to light. They develop more actively in open places but are capable of tolerating shading without a loss of decorative quality. This plastic group includes aquilegia, astilbe, iris, forget-me-not, and ivy.

Photoperiod management and supplemental lighting in greenhouses

Photoperiodism is the ability of plants to transition to flowering only at a certain ratio of light and dark hours of the day. A light pulse is perceived by green leaves, which trigger irreversible changes in metabolism. The duration of the continuous night period plays a decisive role in this reaction.

In open ground, the light regime is regulated by the correct selection of sites: shade-tolerant astilbe, primrose, and hosta are planted in shaded areas. In interiors with low light levels, aspidistra and sansevieria are used. In protected ground, the day is managed technically: it is shortened using shading systems or extended with supplemental artificial lighting (electric light culture).

In winter, due to the low angle of the sun, light intensity outdoors drops by about 15 times compared to summer, and in greenhouses, the glass and structures reduce this figure by another half. Without supplemental artificial lighting in winter, plants will not be able to photosynthesize productively, as natural illumination in greenhouses falls significantly below the critical level.

• Minimum for productive photosynthesis — 2.5–3 thousand lux
• Illumination of plant tops in a greenhouse in winter at noon — 0.6–1.2 thousand lux
• Day length in summer in the temperate zone — 16.5 h
• Day length in winter in the temperate zone — 7 h
• Photoperiodic exposure period for flowering — 1–25 days

Intensive supplemental lighting in the winter period

The winter light deficit in greenhouses critically reduces the intensity of photosynthesis: plants spend more organic substances on respiration than they manage to accumulate. Without supplemental artificial lighting, light-loving long-day crops — carnation, gerbera, rose — slow down in growth and do not produce quality flowering. To compensate for the lack of sun, high-pressure sodium lamps (HPSL) are used, emitting predominantly in the orange-red and blue-violet spectra that are most favorable for plants. Regular cleaning of the glass roof of greenhouses also helps to improve the light regime.

• HPSL illumination intensity — from 3 thousand lux
• Day length for carnation flowering — 14 h
• Illumination for carnation mother plants — 3–6 thousand lux
• Yield increase of carnation in winter — 1.5 times

The duration of supplemental lighting is calculated individually, based on the natural day length and the needs of a specific crop. For example, maintaining a 14-hour day for greenhouse carnation guarantees stable winter harvesting. Winter supplemental lighting of carnation mother plants in a 14-hour mode at an intensity of 3–6 thousand lux allows for obtaining uniform, high-quality, and rapidly rooting cuttings.

Irrigation Calculation and Water Regime Regulation

The moisture demand of ornamental crops directly depends on their belonging to a specific ecological group. It is important for an agronomist to consider the anatomical features of plants to properly design an irrigation scheme and prevent the loss of plantings.

The single irrigation rate and irrigation frequency are determined based on the development phase of the plants, weather, drainage, and soil texture. In open ground, between 4–5 and 25 irrigation sessions are carried out during the growing season. On cultivated loams, the rate for a single irrigation is at least 450 cubic meters of water per hectare. On light sandy and sandy loam soils, this rate is reduced by half, but the number of irrigation sessions is increased.

Plants experience the greatest need for water during the intensive growth phase: in open ground, this period occurs in June – July, and in greenhouses, from spring to autumn. The irrigation scheme is adjusted taking into account the structure of the root system. Crops with shallow roots (primula, garden phlox) require frequent irrigation, whereas taproot plants (poppy, peony) are irrigated less frequently.

Irrigation needs are determined visually by the drying of the topsoil layer and daytime leaf wilting. In open ground, hoses with sprayers, sprinkler systems, or furrow irrigation followed by hilling to retain moisture are used. For small flower beds and gardens, irrigation machines with fine-mist nozzles are used. During the hardening of transplants in hotbeds and during the plant's winter dormancy period, irrigation volumes are minimized.

For the irrigation of ornamental crops, hoses, watering cans of various volumes, sprinkler systems, drip irrigation systems, and subsurface irrigation pipes in benchless greenhouses are used. Supplying water from below and overhead sprinkling are considered the most gentle methods. They do not erode the soil, plant roots are not exposed, and the need for regular loosening is reduced. In pot production, sub-irrigation using the flood method on a rimmed bench shows high efficiency. This method significantly increases labor productivity but requires control of water consumption.

• Labor productivity increase — by 3–4 times
• Bench water filling height — 5–6 cm
• Cyclamen irrigation time on the bench — 1.5 h
• Chrysanthemum irrigation time on the bench — 2 h
• Water uptake by plants — 10–15%

With sub-irrigation, plants use only a small part of the supplied volume. To save resources, the enterprise uses cascade benches. It is also possible to collect the draining water in storage tanks and supply it again to other benches.

Spraying and Plant Hygiene

Spraying is a mandatory element of technology in protected ground. It is necessary during cutting propagation, maintaining stock plants, and preparing bulbous plants for forcing. The procedure is also carried out for 1–2 weeks after transplanting or repotting crops until they root. To increase air humidity in greenhouses, not only the plants themselves are sprayed, but also paths, walls, and benches.

In the winter period, evergreen tropical and subtropical crops indoors often suffer from low air humidity due to heating. The optimal humidity for them is 60–70%, but in winter this figure decreases significantly. A lack of moisture leads to the drying of leaf tips and lobes, as well as the shedding of buds and flowers. To prevent these problems, spray the leaf blades regularly on both sides.

Hygienic care for houseplants includes washing the leaves once a month. This procedure clears the stomata of dust and serves as a preventive measure against thrips and spider mites. It must be carried out according to a specific scheme.

1. Prepare a warm soap solution at a rate of 8–10 g of laundry soap per 200 ml of water.
2. Moisten a soft sponge or cloth in the solution and gently wipe the leaves on both sides, trying not to damage the wax coating.
3. Rinse the treated leaves with clean warm water.

In open ground in flower beds, spraying and washing the leaf apparatus are combined with irrigation by performing overhead watering using sprinkler devices.