Potted Lisianthus:

Secrets of Success – Bedding and Potted Plant Production

by  Brent K. Harbaugh, Robert J. McGovern, and Jim P. Price

University of Florida, Gulf Coast Research and Education Center – Bradenton, FL

Published in Greenhouse Grower, January 1998

 

Part 1 - Plug Production

Part 2 - Bedding and Potted Plant Production

Part 3 - Protecting Lisianthus from Fungus Gnats and other Arthropod Pests

Part 4 - Control Diseases affecting this Crop
 

Although it may not be the easiest to produce, lisianthus has been gaining in popularity as a potted plant each year.  Our second installment in a four-part series on this rising star focuses on bedding and potted plant production.

In our first article, we presented secrets for successful plug production in lisianthus.  If you grow your own transplants for potted lisianthus production, we suggest you read this article.  If you buy plugs from a specialist, we still suggest you read this article since the information and photographs will help you to determine the quality of plugs you are purchasing.  Some of the secrets presented for plug production also apply to potted lisianthus production.

            Lisianthus generally has been placed into one of three categories of use:  cut flower, bedding plant, and flowering potted plant.  Lisianthus grown as bedding plants are produced in 3- to 5-inch pots to be transplanted into the landscape, color bowls, or window boxes.  Florist-quality potted lisianthus are produced in 5- to 6-inch pots.  An additional category has developed in recent years.  Plants are produced in 6- to 8-inch pots for the patio or as large bedding plants (Figure 1) and are usually sold in the same price category as perennials.  This article will cover production aspects for all three categories of potted lisianthus.

Ten Potted Lisianthus Secrets

1.)        Attention to details.  If you are growing the usually top ten bedding plants and think that you can add lisianthus to your production mix without additional attention to details, then you may have serious problems.  Lisianthus requires increased vigilance as far as temperature/photoperiod, cultivar selection, plant nutrition, and growth regulators are concerned.  Simply put, as newcomers to the U.S. ornamental scene lisianthus lacks some of the fine-tuning advancements in breeding and culture that have been developed for other crops.

2.)        Lisianthus demands high soil pH.  Do not underestimate the importance of soil pH for lisianthus.  It prefers a soil pH in the 6.5-7.0 range.  Our research revealed that the ideal pH is 6.78.  As a bedding plant, lisianthus can develop micronutrient toxicity symptoms when grown in a low pH soil.

            In addition to the obvious micronutrient toxicity symptoms of a general chlorosis of  leaves, the more subtle effects caused by low pH include poor root development and loss of overall plant vigor as seen in decreased leaf size, plant height, and number of flowers or floral buds.

            If the soil pH starts to fall below 6.5, a soil drench of flowable limestone should be applied or other corrective actions taken to raise the pH immediately.  Liming materials which contain calcium are favorable since these materials will raise the pH and provide a source of Ca that will benefit leaf expansion.

3.)        Heavy on the K and Ca.  Lisianthus plants are heavy feeders, similar to chrysanthemums or poinsettias.  We have found that a 1N:1.5K ration resulted in high quality plants with excellent postharvest longevity.  Lisianthus also responds to high Ca in the range of 1500 ppm in the irrigation water or fertilizer solution.

Remember, lisianthus grown in low pH soil has a poor root system due to micronutrient imbalances and will not respond to a heavy feed.  Also worth noting, low fertilization rates result in small plants, less basal breaks, and fewer flowers without inducing obvious symptoms of foliar nutritional deficiencies.

4.)        Fungus gnats:  a constant threat.  Fungus gnats can cause partial or complete loss of a lisianthus crop.  Fungus gnats often go undetected even when they have significantly reduced the root system of potted plants.  We have seen crops that wilt in the afternoon that were suspected of being infected with Pythium or other root-rot organisms only to find that fungus gnats had destroyed enough roots to be the causal agents.  Of course, without a normal root system, plants may wilt and develop nutrient deficiencies that prompt growers to increase irrigation and fertilization rates, further damaging the plants or inciting diseases.

5.)        Understanding photoperiod.  We often think of photoperiodic response as a black-and-white response to day length which determines whether or not a plant flowers.  This is only part of the story.  Plant height, number of basal breaks, number of buds, and number of days to flower are also related to day length or interactions of day length with temperature.  In practical terms then, lisianthus growth and flowering are significantly influenced by the time of year the plants are grown. 

            For example, in Florida the largest plants are produced when they are forced to flower in April to mid-June.  Plants flowering outside these months generally will be smaller, have less basal breaks, and fewer flowers (Figure 2).

            We believe lisianthus eventually will be sold by “groups” that perform best at different times of the year, similar to snapdragons.  There have been recent introductions in cut flowers lisianthus for production

of the year. 

            While some cultivars appear almost day-neutral, such as the long day plants (i.e., plants which can flower year round but perform best under long days), and other obligate long day plants (plants which only flower under long days) such as the Yodel series.

6.)        High temperatures are dangerous.  We have shown that high temperatures during the seedling (plug) stage cause rosetting in lisianthus resulting in nonflowering, vegetative plants.  Since we are suggestion transplanting plugs at the 8 to 10-leaf stage, preferable before bolting, high temperatures after potting may still induce rosetting.  Plugs that have greater than 12 leaves and have not bolted usually are rosetted and should not be transplanted to pots.

            For lisianthus, a rule-of-thumb definition for “high temperature” is an average temperature [(the day time high + night time low)/2] of 70º - 75ºF for sensitive cultivars, 75º - 82ºF for most cultivars, and above 88ºF for heat tolerant cultivars.  Optimal temperatures favoring root and shoot growth of most cultivars are 65ºF night and 75ºF day.

            Lisianthus can grow at much higher day temperatures, but caution must be exercised so that the average of the day and night temperatures does not exceed 75ºF, unless heat-tolerant cultivars are used.  Temperatures below 60ºF will significantly slow root and shoot development (i.e., increase production time), but will not hinder subsequent flower development.

7.)                Scheduling, not an easy task.  Days from sowing to flowering depends on cultivar, photoperiod, and temperature.  Thus, scheduling a lisianthus crop to flower on a certain date requires a knowledge of cultivar performance during different times of the year at your particular location.  We have included results from a test where we planted lisianthus biweekly for a year and recorded the flowering date at Bradenton, FL (Figure 3).  Data for three cultivars are presented, but flowering dates are only given when greater than 90% of the plants flowered.

            Although the results would be most beneficial to southern locations, these results can be a starting place for scheduling in other locations.  That is, a few dates could be tested to determine if more or less time would be required to finish a crop at your location without having to duplicate the entire test.

8.)        Plugs per plot.  Currently, the dwarf cultivar in the Lisa and Mermaid series, as well as ‘Little Belle Blue’ and ‘Stormy Skies’, are generally grown as single plugs per 4-inch pot (Figure 4).  We have observed that the dwarf cultivars generally do not last very long in the landscape because they are “too dwarf”.

             While these dwarf cultivars have filled a needed niche, and may continue to do so, we have been developing a series of heat tolerant, semi-dwarf cultivars.  We believe the semi-dwarf cultivars are better suited in the landscape since they have more lower or basal breaks and floral buds.  While they require growth retardants to restrict growth for finishing in 4- to 5-inch pots for the bedding plant market (Figure 5), they have a great longevity in the landscape.  So expect to see semi-dwarf lines for bedding plants in the near future.

             The intermediate size cultivars, such as the Tiara and Maurine series, as well as cut flower cultivars, are grown with 3-plugs per 5- to 7-inch pots.  The number of pluts per pot will depend on pot size, times of year plants are produced, cultivar, and number of flowers or floral beds desired for quality of potted plants being produced.

9.)        Growth retardants a necessity.  B-Nine and Bonzi are the growth retardants of choice for lisianthus (Figure 5).  B-Nine can be applied as a foliar spray, but Bonzi must be applied as a soil drench since foliar (spray) applications are ineffective.  Applications frequency and rate will vary depending on cultivar, times of year plants are being grown, and pot size.     

            Timing of application is very critical.  Since the first internodes on the bolted stem are relatively short, we have found that the first growth retardant applications should be applied at the 3- to 5-node stage.  With Bonzi, one drench application will provide good height control at rates of .125-.25 mg/pot.  With B-Nine, multiple applications are needed.  One or two spray applications of 2500-5000 ppm B-Nine are generally required for height reduction of semi-dwarf cultivars used for bedding plants, and 2-4 applications for Maurine series or shorter cut flower cultivars used for flowering potted plants.

            Depending on the desired look or intended use of the finished pot, one may desire to reduce elongation of the inflorescences.  That is, if the plants are to be planted outside, elongation of the flower stalks is desirable as new flowers will cover the lower spent flowers.  If plants are produced for an indoor flowering potted plant (a florist crop), then late applications to inhibit elongation of the inflorescences would be desirable since the floral display at marketing is the critical factor (Figure 6).

            However, late application of B-Nine may reduce flower size and lighten flower color in some cultivars.  Thus, B-Nine should be tested on a limited basis before whole scale use for late applications.

10.)      Putting it all together.  Since many of the above factors have interactive effects in growth and flowering, it is necessary to consider all these factors to produce a quality plant, especially outside the “easy” months of mid-April through mid-June.  First time lisianthus growers may want to limit production to these months.  As one tries to extend production time on either side of this “safe zone”, the difficulty will increase.

            If year-round production is desired, then most production areas in the U.S. will require heat-tolerant cultivar.  The Maurine series was developed at the Gulf Coast Research and Education Center and has been bred to flower year-round, even at average temperatures as high as 82ºF - 88ºF.  Even with these heat-tolerant cultivars, producing a quality flowering potted plant during summer months is tricky.

            For example, since plant size and flower number decrease during long days and high temperatures (i.e. summer finishing), more plants have to be used per pot while growth retardant application frequency is reduced.  Four to five plus per 6-inch pot of ‘Maurine Blue’ with two B-Nine applications might be satisfactory for finishing plants in July to September, while 3-4 plugs and 3-4 B-Nine applications would produce a larger pot for finishing in May (Figure 7).

            While all these factors may appear complicated or confusing at first, the good news is that when these concepts are mastered, lisianthus has a tremendous potential to be used in many different niches.  As lisianthus breeding continues the production practices become better understood and mastered, we expect to see lisianthus as a potted plant jump into the top 10 bedding and flowering potted plant categories.  In Europe and Asia, lisianthus has already attained this goal as a cut flower, a good indication that mastery of this crop is worth the effort.

Mention of a product does not constitute a guarantee or warranty by the University of Florida or endorsement over other products.  Growers are advised to check registration and label information for all pesticides before the use of a product.