Perennials, flowering plants with lifespans exceeding two years, can flourish in greenhouses, especially if the outdoors experience extreme temperature fluctuations and variable sunlight. Greenhouses provide regular sunlight, regulate temperature, and isolate plants from many pests, enabling the cultivation of high-quality flowers.
In general, perennials require deep enough planting in pots so the roots firmly fasten within the soil. New plants benefit from a loose soil mixture around the roots, allowing the soil to drain and preventing root rot. Even though the soil requires moisture, plant leaves cannot remain wet for extended periods since it can lead to mildew. Therefore, greenhouse setups provide a fan-enabled air circulation system to evaporate excess moisture quickly. When perennials become diseased, individuals must remove them immediately so they do not infect other plants in the vicinity.
Commercial perennial growing operations must provide the optimal environment to maximize the species' production and generate the highest-quality flowers. Therefore, most will group perennials based on their needs spanning irrigation, temperature, and photoperiod.
Growers must consider the underlying mechanisms of flowering. Forcing programs utilize temperature and light to force flowering and maximize blooming potential across the flowering season—understanding plants' cold requirements and providing cold treatments as necessary benefits the species' potential. For example, many spring-blooming plants need a chilling period to break the dormant stage and should be grouped.
They require a specific number of hours between 32 and 45 degrees Fahrenheit. Then, the plant becomes primed to resume growth and achieve vernalization, or spring flowering. In controlled greenhouse settings, the plants may benefit from a tiered approach. Cold plants scheduled for sale at earlier dates would require chilling to produce flowers first and with more uniformity.
Forcing perennials has additional requirements focused on photoperiod, or the number of hours of light within a 24-hour period. The strategy changes throughout the year in temperate climates. For a broad range of floriculture crops, the amount and duration of light control flowering and growth. Even a small shift may represent the difference between rapid flowering and vegetative, non-flowering growth.
When forcing long-day plants, it's essential to provide lighting until the natural photoperiod reaches above 14 hours a day, applicable to most flowering perennials. Not enough lighting can result in sporadic flowering and few flowers on the terminal shoots, with lateral branches simply remaining vegetative or hiding the few flowers that finally emerge. Some perennials have short-day requirements and actually flower or flower more rapidly in situations with shorter lighting. Day-neutral plants flower without regard to day length. However, the lighting setup will still influence the height they reach and growth characteristics such as branching.
When growing perennials, it's also important to prune to direct and encourage flower-producing growth. As they mature, give the root systems room to develop by transplanting the plants into larger containers. Arranging larger plants in a section of their own, away from smaller plants, helps ensure that each group gets the proper irrigation, light, and temperature for ideal growth (without crowding out neighbors). As with any agricultural setup, greenhouse weeds remain a persistent issue. Pull them the moment they surface before they have time to germinate and seed.
