By Jovita Turan, 26 April, 2020
Lisianthus (Eustoma grandiflorum (Raf.) Shinn), belongings to family Gentianaceae, is a native species distributed in the North American prairies: from southern Nebraska to Louisiana and Texas. This herbaceous ornamental plant has a biennial cycle, however, it is normally cultivated as an annual plant. Moreover, with the use and adaptation of the acclimatized environments and specific varieties with respect of the time of the year, year-round production of the plants can be maintained.
Lisianthus is officially called Eustoma and it is derived from the Latin name Eustoma russellianum Grandiflorum. The name Lisianthus is a composed of two Greek words and is referred to the taste of the flower: “Lysis” which means bitter and “Anthos” – which means flower. The name Eustoma translated means ‘good mouth’, where “Eu” represents good and stoma – mouth.
The seeds of Eustoma has already been included in Park Seed Company catalogs in 1887, while as a new cut flower, lisianthus was offered in the early 1980‘s in the United States by Sakata Seed Company. Now Eustoma is an important ornamental plant product in South East Asia, including Indonesia. In the Arava Valley of Israel, lisianthus is planted in the early fall for offseason export to Europe in the winter and spring months. It is commonly cultivated for sales as a cut and pot ﬂower with a remarkable rose-like ﬂower, varying in size and shape, colorful, long stems and with a long vase-life which could be even up to 6 weeks. In addition, the plant is tolerant to the pathogen, soil acidity condition, and high-temperature stresses.
It can be stated that Lisianthus is a well-established crop, and has made a tremendous impact on cut flower markets with other cut flowers such as roses, carnations, or chrysanthemums that have been grown as commercial cut flowers. The production and popularity of the plant have grown worldwide, and they are considered one of the ten best-selling cut flowers. As the flowers and buds may last for long periods of time out of the water without wilting they are a favorite for wedding bouquets, corsages, boutonnières, and head wreaths.
The plant grows up to 15 - 60 cm tall and 15 – 30 cm in width with bluish green, oval, slightly succulent leaves.
Lisianthus mature rapidly, and produce beautiful funnel-shaped flowers growing on long straight stems. Flowers of the plant can be single or double, in a variety of colors and bi-colors. The mature flower has a calyx of five sepals, a corolla of five petals, five stamens attached to the corolla throat, and a single-celled ovary with two stigmata. Sepals on Lisianthus are only fused close to the base and are much smaller than petals. The petals form a trumpet or funnel-shaped corolla and are often yellow on the inside close to the mouth of the flowers. The stamens of the Lisianthus are inserted close to the base of the petals along with long and slightly twisted anthers. The Lisianthus stigmas are bilobed.
The most common colors are pink, purple, red, white, lavender to blue, and yellow. Nevertheless, more and more new colors and species are being introduced on the market such as with two-toned flowers or flowers with trimmed edges.
Temperature is a key factor affecting lisianthus flowering. It interacts with the developmental stage of the plant: at the seedling stage (up to 4–5 true leaf pairs), temperatures above 28.8C during the day delay bolting and above 23°C at night can induce rosetting while low temperatures slow down growth but speed up flowering. After bolting, high temperatures accelerate development, floral transition, and flowering. The best temperature for growth where the minimum temperature is above 15°C and the daytime maximum temperature is less than 25°C.
Lisianthus should be grown in well-drained soil that is rich in organic matter with a pH of 6.5–7.0 as well as free from pest- and disease. They favor high calcium levels as well as adequate phosphorus. Moreover, a good drainage is essential.
Conventionally, Eustoma grandiﬂorum is propagated vegetatively by cuttings and sexually by seeds.
One pelled seed should be placed per cell into a deep cell tray using a well-drained media. Seeds should not be covered because germination requires high light, however, a thin layer of fine vermiculite covering the seed will help to control algae growth. It can not be allowed the growing media to dry out during germination as adequate moisture is needed to dissolve the pellet coat around the seed. The temperature should be maintained at 20 to 21°C with a good air ventilation. Germination of seeds lasts 10 – 14 days.
After emergence, cell trays should be placed in a location where they will continue to receive good air circulation.
Seedlings of lisianthus are slow growing seedlings, typically time can take from 9 to 11 weeks. The recommended temperature during the night is between 15°C and 25°C. Seedlings are sensitive to high salts but Calcium Nitrate based and well-balanced soluble feed helps to promote strong, thick stems later in crop life cycle.
The seedling can be transplanted at fourth true leaf stage or as soon as the young plant can be pulled from the tray. It should not be allowed to the plants to get root bound as this can cause the flowers to bloom earlier on short stems, especially during long days. Plants should be spaced 10 – 20 cm apart, directly in the greenhouse soil or in the field without burying the seedling too dee. Plants have to be kept evenly moist through the vegetative stage. Once buds are visible water levels should be reduced to avoid soil-borne pathogens. Lisianthus should not be let to wilt and stress. It is recommended to keep temperatures at 24°C–27°C during the day and 16–18°C during the night. Finishing times range from 12 weeks from transplant in summer to 22 weeks from transplant in winter.
Most cut flower cultivars of lisianthus are multiplied by F1 hybrid seeds and sold for cultivation. As cultivars represent a population of hybrid individuals derived from crosses between heterozygous parents, the use of a true F1 hybrid would improve the uniformity and quality of the product.
However, the vegetative method is laborious and time-consuming and the seed technique is hampered by cross-pollination and is not efﬁcient because of a low seed germination rate of 34-39%. The seeds are extremely small: 19,000 seed /g which lead to hard plantings in the field and progeny is not uniform and inconsistent, displaying rosette.
Considering the high demand for this ornamental plant, tissue culture seems to be the most advantageous propagation method as well as it is one of the best ways to prevent wide variation due to plant seeds heterozygous character and long development period of the plant which take at least 4.5 months or more to reach the ﬂowering stage.
Different groups of lisianthus are available for various climates and growing seasons. Due to these varying conditions, it is essential to select a variety bred to perform for desired harvest period. Moreover, it is good to ensure the maximum stem length depending on the climate and growing season.
Group I typically is sown for transplanting in winter months (it is early flowering), Group IV are the latest to flower and will withstand more heat and longer days of summer while still producing strong, tall stems.
Management in the greenhouse
It is recommended to grow lisianthus in the greenhouse or another protected structure to protect flowers from rain as it causes spotting on the petals (especially darker flower colors). However, in the greenhouse cover materials must be monitored carefully in the case to avoid condensation development which creates droplets and lands on the plants.
At later stages, during stem elongation and flower bud initiation (when bud meristem starts its formation), higher temperatures, higher light intensity, and long day (LD) treatments can hasten plant development and flowering. The effect of photoperiod on flowering is cultivar dependent, and lisianthus is usually regarded as a facultative LD plant. However, high temperatures can significantly delay flowering of the lisianthus. The general practice in the hot region is to shade Eustoma plants at planting in order to reduce temperatures in the greenhouse. The duration and intensity of the shading may lead to considerable variation in growth, development, flowering time, and flower quality. To avoid the negative effects of shading, moderate temperatures should be maintained at planting via a cooling system or only much lighter shadings used. Long day conditions accelerate floral transition and flowering. A study conducted in Norway showed that increasing the daily light integral from 4.4 to 8.8 mol m -2 day-1 while using high-pressure sodium lamps, under long day conditions induced early flowering in lisianthus.
Water should be supplied in the morning, best – by drip irrigation. Overhead irrigation can be used until the plants start to flower. On sunny days proper ventilation should be supplied to reduce the temperature in the greenhouse by opening the vents, using white-on-black mulch to keep the soil cool. Additionally, mulch helps in weed control by suppressing weeds.
As many studies had shown the use of differentiated light transmission networks in protected cultivation has presented promising results in increasing productivity and precocious development of some ornamental plants. In the case of the use of a light transmitting nets for growing Lisianthus red color is recommended as it leads to greater height and more accelerated growth.
To support the stems and keep then straight during the development, one or two layers of horizontal netting can be used.
Harvest should be done when one or more flowers are open. Harvesting or pinching the first bloom will result in a more uniform set of blooms per stem. If the first bud/flower is removed, the same stem can have 2 to 7 open flowers, increasing the value of the crop significantly. The harvested first bloom is useful in corsages, small bud vases, or short arrangements.
Lisianthus is best picked in the morning when temperatures are at their coolest. Plants should be placed straight into a cool room at 2–5°C, in a solution of very clean water, with a ‘preservative’ added to increase the length of vase life. Many types of ‘preservatives’ have been reportedly used successfully, such as a continuous use of 2 to 4% sugar or pulsing with 10% sugar, plus an antimicrobial material.
Pests and diseases
Aphids, thrips, whiteflies, and leafminers cause significant damage in their own right, and the first three of these are also vectors for viruses. Viruses cause the usual symptoms - leaf yellowing, mottling, chlorosis and distortion and poor flowering. Tomato spotted wilt and impatiens necrotic spot viruses are spread by thrips, bean yellow mosaic virus by aphids, tomato yellow leaf curl virus by whiteflies, and tobacco mosaic virus by humans.
Fungal diseases include Botrytis (grey mould), Fusarium, Myrothecium, Peronospora (downy mildew), Phytophthora, Pythium, and Thielaviopsis. Poor drainage combined with hot or humid weather can lead to major problems with root rots and stem blight (Sclerotinium rolfsii).
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