How to Grow and Care for Lisianthus (Prairie Gentian)

Lisianthus flowers (Eustoma spp.) are tender perennials or biennials often grown as annuals. Also called prairie gentian, they natively return yearly in prairies and fields from northern Mexico north to Colorado and Nebraska. Lisianthus plants are about 1 to 3 feet tall, featuring large purple and white bell-shaped flowers with flaring lobes that bloom on one or more upright stems.

They can be somewhat finicky to grow and care for but are worth the effort if you like cut flowers. Cut lisianthus flowers can last about two weeks and bloom in summer and fall. Depending on your regional climate, they may bloom in June or July and continue until September or October. Deadheading spurs more blooms. They are celebrated for looking like a rose but lasting longer in the vase.

Lisianthus is in great demand for bridal bouquets and other special-occasion arrangements. Lisianthus colors commonly come in white, pink, purple, and cream, but you may occasionally see yellow, apricot, rose, or red. The flower's foliage is dark green, lance-shaped, and slightly fleshy in texture.

As an annual garden flower, lisianthus planted from seeds grows slowly, reaching flowering maturity in five to six months. Most gardeners plant them from commercial nursery plants that were started from seed in greenhouses the previous fall so that they will erupt in fluttery, layered blooms by spring.

Lisianthus Care

Depending on your growing zone, lisianthus can come back each year. Lisianthus is an annual in all zones and a perennial or biennial in zone 8 or warmer, meaning it grows back in frost-free regions. While you can grow lisianthus from seed, doing so is not advisable for beginner gardeners since the tiny lisianthus seeds take a long time to mature into blooming-sized plants unless cultivated under strictly maintained greenhouse conditions.

Your best bet is to plant nursery starts in spring, carefully choosing lisianthus plants with buds or emerging flowers (greenhouse growers sometimes produce plants that favor foliage over flowers).

Lisianthus is not easy to grow. This plant has earned a reputation as a fussy plant. Ideal soil, careful watering, precise feeding, and frequent staking are required for growing the prized flower stalks favored by floral arranging hobbyists.

Light

Plant your lisianthus in a spot that boasts full sun, where the plant can get at least six to eight hours of sunlight a day. If you live in an area with very hot summers, the plants will benefit from afternoon shade, but don't worry too much. The more consistent sunlight your lisianthus gets, the better foliage and flowers your plant will have.

Soil

Choose a planting site with well-draining soil. Raised beds are ideal, as are containers. Lisianthus prefers soil rich in organic matter such as manure, compost, or leaf mold. The soil should be well-draining and not remain waterlogged, which can lead to root rot.

Lisianthus flowers cannot tolerate very acidic soil pH. Nor does it like alkaline soil. Maintain a soil pH between 6.5 and 7.0 to prevent your lisianthus plants from developing yellowing of the leaves and decreased vigor.

Water

Keep your lisianthus plants moist, but never allow them to remain soggy. Overwatering your plant can encourage the development of fungal diseases. If you have the time to create one, a drip irrigation system can give your plants water at their roots, right where they need it. The plant's soil should be allowed to dry out in between waterings, but don't let the plants themselves dry out. Getting the irrigation timing correct can be a challenge when growing lisianthus. About 1 inch of rainfall/irrigation per week is ideal for lisianthus.

Temperature and Humidity

Lisianthus is a heat-loving plant native to areas where the days are relatively dry and the summer nights are warm, though they will flower more profusely if given more moisture. They do not mind hot conditions and can even tolerate a bit of drought, which may reduce the flowers. But lisianthus is not tolerant of humidity and does not do well in damp climates with limited sun, such as those in the Pacific Northwest.

Fertilizer

Lisianthus flowers need a constant nutrient stream to produce well-branched plants with abundant blossoms. Choose a flower fertilizer with one and a half times the amount of potassium as nitrogen, and apply it according to package directions throughout the plant's growing season. Lisianthus require regular feeding, and more often if rainfall is frequent.

Types of Lisianthus

There are many lisianthus varieties, distinguished by their color and size. Most lisianthus plants bloom best in early summer, although an increasing number of cultivars are being introduced that continue to bloom through the hottest summer months and into fall.

• 'Balboa': This lisianthus variety is full of blooms, boasting upwards of a dozen flowers per plant, all in shades of blue.
• 'Flamenco': Although gardeners seem to prefer double-flower lisianthus plants over single-flower ones, the heat tolerance of this lisianthus variety makes this type worth a try.
• 'Maurine': This plant is a semi-dwarf, heat-tolerant variety, making it the perfect size to grow in containers on your deck and patio.
• Sapphire Pink Rim': This lisianthus variety is compact (5 to 6 inches tall) with white blooms and pink edges.
• 'Echo Blue': This tall lisianthus variety (up to 34 inches) has dark blue flowers and blooms from midsummer up to frost.

Pruning

If you've successfully grown lisianthus plants that have erupted in blooms come early summer, there's a good chance that you can coax a second act from the plants in the fall. To do so, it's important to prune the plants in a certain manner.

Start by cutting the plant's stems back to the basal rosette of foliage after their initial bloom. Then, give your plants all the pampering they crave, including thorough weeding, regular irrigation, and plenty of fertilizing. By mid-September, you should harvest new blooms to pretty up your fall bouquets.

Propagating Lisianthus

In warm-winter zones where lisianthus is perennial, it is sometimes propagated by taking root cuttings in winter:

1. After cutting back the stems and foliage to just above ground level, dig up the entire plant with a shovel.
2. Divide the root ball into sections with a sharp knife or trowel, ensuring each section has some greenery or growth buds.
3. Immediately replant the pieces in their desired locations and water thoroughly. New growth should begin within a few weeks.

How to Grow Lisianthus From Seed

Starting lisianthus from seeds is a long, drawn-out process best tackled by serious gardeners. Lisianthus seeds are very small—barely larger than dust particles—so growing plants from seeds is impractical. When purchased commercially, lisianthus seeds are often prepared in the pelleted form to make them easier to handle. In cold-winter zones, start the seeds indoors in late fall. In warm-winter perennial zones, you can plant lisianthus seeds directly in the garden in late summer.

For indoor seed starting, use trays or small pots filled with a porous seed-starter mix (fine peat moss plus fine vermiculite). Moisten the potting mix and sow the lisianthus seeds on the surface. Cover the tray or container with a plastic dome or clear plastic bag and set it under grow lights (seeds need 16 hours of light per day to germinate and sprout). For the next two weeks, carefully monitor the temperature and keep it between 70 and 75 degrees Fahrenheit.

When seedlings appear, remove the covering and lower the grow lights to just above the seedlings. Seedlings can tolerate temperatures that fluctuate slightly but keep it between 60 degrees and 75 degrees Fahrenheit. Continue growing the seedlings, ensuring the growing medium stays moist but not soggy. Feed with a general-purpose fertilizer diluted to half-strength each week.

After seven or eight weeks, each developed seedling can be transplanted into a container filled with potting mix. As you grow the seedlings, ensure temperatures do not exceed 75 degrees, or you risk sending the plants into a dormancy phase (known as "rosetting").

Several months later, as spring arrives, your seedlings should be about 4 inches tall and can be hardened off with increasingly long visits to the outdoors over a week or so until they are toughened up for planting in the garden. However, don't plant until all danger of frost has passed.

Potting & Repotting Lisianthus

Shorter varieties of lisianthus grow well in containers filled with ordinary potting medium. Their colors combine well with many plants in mixed containers, such as dianthus, coreopsis, baby's breath, and snapdragons. In zones where they can remain outdoors as perennials, potted lisianthus plants require annual repotting, going up one pot size each time.

Though challenging, some gardeners find it possible to keep potted lisianthus plants growing indoors and flowering through the winter. The trick is giving them enough bright light, controlled temperatures, and preventing common indoor pests such as mites and fungus gnats from decimating them. During the indoor winter, provide the plants with a weak monthly feeding with diluted fertilizer.

Overwintering

In cold-weather zones where lisianthus dies out, pull the plants from the ground after the blooms are complete or when cold weather causes the plants to wither.

In warm-winter zones where lisianthus grows as a perennial, simply keep cutting back faded flower stalks for continued blooms; reduce feeding during the winter months. Zone 7 is a transitional zone for lisianthus; it may survive the winter if you cut back the plants to ground level and cover it with a light mulch until spring.

Common Pests & Plant Diseases

Fungus gnats are one of the most common pests lisianthus plants deal with, and they can travel with the plants from early on in the greenhouse stage. The flying adults aren’t the problem, but rather the larvae that live beneath the soil and feed heavily on roots, devastating your plants. To rid your plant of fungus gnats, focus on not overwatering. You can also treat the plant with a mild insecticide or neem oil until all signs of an infestation have gone. Mites are another common pest that can be treated with neem oil or insecticide.

Lisianthus plants can also be susceptible to some plant viruses and stem cankers. Affected plants must be removed and discarded.

How to Get Lisianthus to Bloom

Proper sun, watering, and feeding are the primary needs for lisianthus blooming success. Problems with poorly blooming lisianthus can usually be traced to cultural issues. Lack of nutrients is the most common reason these plants fail to bloom robustly.

The plants need a good amount of sun; like many heavy-flowering plants, they require regular feeding. Proper watering is also critical. Lisianthus needs regular deep watering applied as soon as the soil dries out, but it does not like sitting in wet soil. Deadheaded lisianthus for continual blooms. Cut each spent bloom back to where it emerges from two sets of leaves.

Common Problems With Lisianthus

Lack of full flowering is the most common problem with lisianthus, but several other issues make this plant challenging to grow.

Plants Topple Over

The long stems that make lisianthus flowers so elegant in the vase can be a drawback in the garden, as the stems are often too thin to support the double-bloomed varieties. Don’t let this discourage you, though, as there are so many beautiful and functional grow-through supports on the market, from nearly invisible support rings and grids to decorative willow or metal cage-like tuteurs (pyramid-shaped supports).

Cut Flowers Don't Last

Lisianthus flowers can last up to four weeks if you use a few tricks:

• Harvest the flower stems early in the day, as the first buds are just opening. Use sharp scissors to cut the stem off just above the basal foliage. The light-green buds will gradually transform into full color as the flowers open.
• Remove the leaves below the waterline and recut the stems as you arrange the flowers in the vase.
• Replace the water every two or three days—or whenever the water begins to get cloudy.
• Add 1/4 cup of sugar to each quart of water to prolong the blooms. Subsequent water changes require 1/8 cup of sugar per quart.
• Add a few drops of household bleach to the water to reduce bacteria.

Flowers Aren't Nice Enough for Cut Arrangements

Remember, lisianthus plants that florists use in commercial flower arrangements have been grown in carefully controlled greenhouse conditions, with regular feeding, controlled watering, and many chemicals to control pests and diseases. Don't expect your outdoor garden flowers to be perfect.

If you are serious about flower arranging, plant a large patch of lisianthus and be prepared to tend them carefully to ensure the best possible blooms. In a large patch, your chances for a good number of perfect flower stems are much better.

But even when imperfect, lisianthus flowers are great citizens of the mixed border. The answer may be to enjoy them where they are rather than to insist on perfect flowers for cutting.