Innovative flower forcing methods for year-round bloom in commercial floriculture

Flower forcing is a vital technique in floriculture that enables the controlled induction of flowering in major flower crops outside their natural blooming seasons. This review compiles advances in environmental, chemical, and mechanical methods used for flower forcing in crops such as chrysanthemum, marigold, rose, tuberose, and jasmine. Key factors influencing flowering—temperature, photoperiod, and plant growth regulators—are discussed alongside case studies demonstrating practical applications. Methods like photoperiod adjustment, pruning, application of gibberellins, paclobutrazol, and ethylene-based treatments have been shown to significantly enhance off-season flower production, flower quality, and yield. Flower forcing not only stabilizes flower supply and market prices but also supports farmer income and employment throughout the year. The review concludes that integrating crop-specific forcing strategies can effectively address market demands while optimizing floricultural production systems.

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Introduction

Flowering behavior in plants varies according to environmental factors such as temperature and photoperiod, as well as the plant's genetic constitution. Based on these factors, plants can be broadly classified into two groups: all-year-round flowering plants and seasonal flowering plants. In all-year-round flowering plants, some species show little or no seasonal influence and bloom consistently throughout the year, as seen in roses, marigold, chrysanthemum, and heliconia. Others in this group show great seasonal influence, with flowering peaking under favorable climatic conditions, such as in jasmine and dendrobium orchids. Seasonal flowering plants, on the other hand, bloom only during specific seasons. Their flowering is either influenced by temperature-especially low temperatures as in tulips, amaryllis, and daffodils-or by photoperiod. Photoperiod-influenced plants are further divided into short-day plants, which flower when day length is shorter than a critical value (e.g., poinsettia), and long-day plants, which flower when the day length is longer than a critical value (e.g., Siam tulip). Due to this varied flowering behavior, flowers available in their normal season are often abundant and fetch lower prices, whereas flowers are in high demand and command better prices during the off-season or on special occasions like Valentine's Day, Mother's Day, and festivals. To take advantage of this, farmers adopt flower forcing techniques, which involve inducing flowering at desired periods by manipulating factors such as photoperiod, temperature, fertilizer application, plant hormones, pruning, leaf trimming, ringing, and breaking dormancy. Flower forcing allows for the production of flowers during off-seasons and specific dates, helping growers meet market demand and achieve higher profits.

Objectives

The purposes of inducing plants to flower during the off-season or on specific dates are as follows.

Lotus (Nelumbo nucifera)

Lotus flowers year-round but requires standing water. The forcing technique in lotus varies with the season. To maintain consistent blooming during winter when temperatures drop, lowering the water level to 50 cm helps increase water temperature, ensuring flower size and quantity comparable to summer. During summer, when high temperatures can accelerate growth and early flowering, raising the water level to 75 cm from the winter level helps cool the water, maintaining stable flower production and size. To handle additional rainfall, maintaining a 50 cm water level is recommended, allowing rainwater to raise the level slightly without affecting the blooming process.

Jasmine (Jasminum sambac)

Jasmine typically blooms from March to June, continuing until October. Flower production and quality decline from November to February. By shifting the pruning period earlier to September instead of the usual late November, flowering can be promoted during the winter lean period, increasing both yield and flower quality. This adjustment led to a 2.67 times higher yield compared to November pruning. The benefit-cost ratio also improved significantly, reaching 2.51 versus 1.66 under conventional practices, thereby enhancing farmer profitability.

Roses (Rosa hybrida)

Although roses bloom year-round, peak flowering is seen during cooler seasons. To produce flowers around Christmas and New Year, pruning is recommended in November, as flowering generally occurs about 43 days after cutting. For flowering timed around February 10th, cutting the flowers on December 23rd is advised, with blooms appearing approximately 49 days later. This scheduling ensures flowering aligns with specific festive periods.

Gladiolus (Gladiolus grandiflora)

In cooler regions, flowering in gladiolus can be encouraged by preheating the corms for two weeks at temperatures between 27 °C and 32 °C before planting. This treatment stimulates earlier flowering. In warmer regions, a different method is suggested. Corms are soaked in a gibberellic acid (GA) solution at concentrations of 10 to 25 ppm prior to planting, which speeds up flower primordia development and promotes quicker blooming.

Research outcomes

The study by Sangma et al. (2016) [20] evaluated the effect of different covering materials like tarpaulin, HDPE, and black satin cloth on off-season cut flower production in eight chrysanthemum cultivars. The results showed that covering materials successfully induced early flowering compared to natural photoperiod conditions. Among the treatments, HDPE proved most effective, producing plants with optimum height, controlled plant spread, the highest number of cut stems per plant, early visible flower bud formation, and longer flowering duration. While black satin cloth resulted in the tallest plants and greater plant spread due to its partial light transmission, HDPE and tarpaulin produced sturdier plants with better commercial traits. Cultivars such as Tata Century, White Star, and White Bouquet responded quickest to short-day treatment under HDPE, requiring only eight weeks to flower. The study concluded that HDPE is the most suitable covering material for off-season chrysanthemum production, offering advantages such as effective artificial short-day creation, lighter weight, ease of handling, and suitability for all tested cultivars. The study by Sathappan (2018) [21] [30] evaluated the effect of different winter pruning dates on the growth and flowering performance of Rosa centifolia. Five pruning dates from mid-December to mid-February were tested. The results showed that pruning at the end of December (T [29] evaluated the effects of different planting dates and varieties on the growth and flowering of tuberose under winter greenhouse conditions in Tianjin, China. Two varieties, 'Single' and 'Double,' were planted on October 30 th , November 30th, and December 20th to observe differences in dormancy release, flowering behaviour, and flower quality. Results showed that earlier planting, especially on October 30 th , produced superior outcomes in both varieties, with 'Double' performing better than 'Single' in terms of corm sprouting rate, number of florets, spike length, and overall flower quality. October planting of 'Double' variety produced cut flowers comparable to field-grown tuberose, while later plantings resulted in reduced quality due to lower temperatures and shorter photoperiods. The study concluded that for winter forcing cultivation of tuberose, planting 'Double' variety in October is most suitable to achieve higher sprouting, better flowering characteristics, and superior quality cut flowers in greenhouse conditions. The study by Kalaimani et al. (2017) [12] evaluated the effect of different pruning times and plant growth retardants on the growth and off-season flower production of Jasminum sambac (cv. Ramanathapuram Gundumalli). Results indicated that pruning during the last week of September, combined with foliar application of mepiquat chloride (MC) at 150 ppm, significantly improved vegetative growth parameters such as plant spread, number of primary and secondary branches, and ultimately led to the highest flower yield during the off-season (December to February). This treatment (P2T9) produced the greatest number of flower buds per cyme (7.70), highest weight of 100 flower buds (28.00 g), and maximum flower yield per plant (222.47 g) and per hectare (1423.81 kg). Early pruning helped plants benefit from longer photoperiods and higher temperatures, while mepiquat chloride redirected resources from vegetative to reproductive growth, enhancing flower production. The study concluded that combining September pruning with MC 150 ppm spray is an effective strategy to boost off-season flower yield in Jasminum sambac.

Conclusion

Flower forcing is a key practice in floriculture that allows growers to control flowering time, ensuring consistent flower availability throughout the year. By enabling offseason and date-specific blooming, it helps meet market demands during high-value periods, increases farmers' income, and minimizes surplus and wastage during peak seasons. Overall, flower forcing supports year-round flower production, stabilizes market supply, and enhances grower profitability and consumer satisfaction.

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