My Newest Favourite Flower

By Marilyn Homewood, Master Gardener

One of the new plants that I tried this year was Lisianthus (Eustoma grandiflorum) also known as prairie gentian. Lisianthus are flowering plants native to northern Mexico and the Great Plains in the United States and as with most prairie plants, they love the heat and are quite drought tolerant. I thought they just might work in my growing conditions. The plants are hardy in USDA zones 8 to 10 and are grown as annuals here in Ontario. Their flowers come in a wide range of colours, are double or single, can be very ruffled and are reminiscent of a rose. They produce multiple buds on a single stem and one stem can bloom over a 3 week period. A single stem will last around 2 weeks or more in a vase. Plants bloom around late July/August and if pruned back when finished, a second smaller flush should bloom in September. What a treat in August when almost everything else is flagging in the summer heat to have this beauty bloom! A welcome sight in that period before the dahlias really get going.

Is there a down side? Lisianthus has a bit of a reputation of being difficult to grow. They are very slow to germinate and grow. Here in Ontario, seeds should be started in early January. I can’t speak to that personally as I was able to purchase plugs in April in order to give the plants a try. I will attempt to start seed this winter. There are Lisianthus seed starter groups on line where lots of information and assistance.

Note that these blooms had been in this pot for 2 weeks when the photo was taken!

Seed/Variety Selection

Lisianthus produce tiny seeds hence most of the seed that you purchase is coated to make handling easier (NB coated seed does not store well from season to season). A number of different series are available and varieties of lisianthus are grouped by bloom season (similar idea to the classifications of snapdragons). Flowering is stimulated by three factors; Temperature (warmer temperatures accelerate flowering),Light intensity (high light intensity accelerates flowering), and Day length (long days accelerate flowering). By using varieties from Group 2 and Group 3 you can have blooms over a longer period of time as they have different bloom periods.

Cultural Requirements

Lisianthus is a heat-loving plant but it doesn’t like direct afternoon sun. Ideally it should have full morning sun and part shade in the afternoon. The lowest temperature lisianthus can survive outdoors is -12°C and many growers feel that the plant benefits from being planted out before the last frost in order to get their roots established. Lisianthus prefers to have an even amount of water on a regular basis. If it doesn’t rain often, the plant will need to be watered for the best performance. I neglected to do this (got busy with dahlia issues) and the lack of water was reflected in stem length and bud count but the flowers seemed unaffected (I still had 5-6 buds on each stem). The blooms were wonderful. Recently I visited someone who had watered their plants: they were twice as tall and had even more buds than mine. Lisianthus can be subject to botrytis hence it’s important to water at the base of the plant. Well-draining soil with a neutral to slightly alkaline pH is preferred. These plants are happy with a feed of compost and if you’re feeling keen, the occasion feed of fish fertilizer.