Consider New Stock Options

Stock (Matthiola incana) is an underappreciated workhorse of the cut flower industry. It lacks the panache of roses and lilies and the postharvest durability of chrysanthemums and carnations, but stock offers wonderful fragrance and a broad range of colors.

Production and Shipping Limitations

Stock production in the United States is primarily outdoors and limited to areas with temperatures low enough to provide flower initiation and high-quality stems. These are areas where the temperatures are not so low as to damage plants, which usually means only light to moderate freezes.

Most commercial production has been in coastal California with flowers shipped nationwide. However, growers in parts of the Southeast can also produce high-quality stock during winter, and growers in the North can do the same in spring and early summer. Smaller amounts of stock are grown in spring across the United States and Canada.

The increased use of greenhouses and hoophouses for season extension of cut flower production presents another opportunity to grow stock for local markets. 

While stock can handle cold storage well, its leaves are somewhat brittle and tend to crack when packed and shipped in boxes. The foliage also tends to yellow fairly quickly, especially when stored and shipped.

Production Options

For many years, growers had two options regarding stock cultivars: traditional types and minimal-cold-requirement types.
    
Traditional types are tall, up to 3 feet, but require a cold treatment of 50-55F for at least 10 days for early-flowering cultivars,and three weeks for late-flowering cultivars. Many colors are available.
    
The cultivars in the traditional group can be divided into selectable and nonselectable plants. While double-flowered stock are more valuable commercially, no series available produces 100 percent double flowers. Most stock cultivars produce 50-60 percent doubles and 40-50 percent singles.
    
Seedlings of selectable types can be sorted into doubles and singles with some practice and the right environmental conditions. The single-flowered forms of selectable cultivars have darker green leaves, slower germination, and less vigorous growth than the double-flowered forms. Leaf color differences are to be more easily seen when seedlings are grown at 50F (10C) or lower. Consequently, reduce temperatures to 39 to 46F (4 to 8C) for 8 days after the cotyledons are fully developed. The culling process is tedious and a person with experience should be given this task because seedling differences are often not obvious. Selectable series include Glory and Goldcut. Nonselectable cultivars are a mixture of singles and doubles and include ‘American Beauty,’ ‘Lilac Lavender,’ ‘Miracle Rose Pink’ and ‘Pacific Blue.’
    
Minimal-cold-requirement types are white or cream-colored cultivars that flower with little or no cold treatment and have a short crop time, 10-14 weeks from sowing to flower. These cultivars are almost all doubles (about 90 percent) and better adapted to greenhouse or hoophouse production. Cultivars include ‘Cheerful White,’ ‘Cheerful Yellow’ and ‘Regal White.’

New Series Require Minimal Cold

Both Sakata Seed’s Vivas series and PanAmerican Seed’s Katz series require little or no cold treatment. These series can initiate flowers at relatively mild temperatures (55-60F), eliminating the cold treatments necessary for most cultivars. This feature makes them suitable for greenhouse and season-extending hoophouse production. Hoophouses can be used to protect plants from the worst cold weather that can cause damage.
    
Plant quality is best under low temperatures (50-55F), but plants can grow well under higher temperatures (up to the low 80s during the day). They are available in more colors, including various shades of rose, pink and purple. Unfortunately, they produce only 60 percent doubles. Plants are not as tall (about 2½ feet) as traditional column types and as with all stock cultivars, they don’t like high temperatures (above 62F at night or above 85F during the day) during production.
   
The Katz series was initially sold as Mambo, but the name was changed to honor deceased PanAmerican Seed breeder and cut flower specialist Philip Katz.  He was also a well-respected and active  ASCFG member.
 
Producing ‘Vivas Blue’

‘Vivas Blue’ plants were grown from 392 plugs in a greenhouse at North Carolina State University. Large plastic flats (20 3/4 by 15 inches, 4 1/2 inches deep) were filled with a commercial peat-based medium. Plugs were planted in a 4-by-6 pattern, 3-by-3 inches apart, resulting in 24 plants per tray. Bulb crates would work equally well. For part of the crop, standard shallow bedding plant flats (10 1/2 by 21 inches, 2 1/2 inches deep) were used. They worked well, but the growing medium dried out faster due to having less volume in the flat.
    
Plants were grown at minimum temperatures of 55F night and 65F day, although many nights and days were warmer. Plants were irrigated with 150 parts per million nitrogen from either a 20-10-20 or 13-2-13 fertilizer, as needed. While the stems are quite stocky (no pun intended), one or two layers of support netting should be used in the greenhouse to hold up the heavy inflorescences.
    
Timing of the crop varied with the planting date. Plugs were planted on three dates: Jan. 13, Jan. 20 and Feb. 10. The finished crops started flowering March 14, March 22 and April 3, respectively. The crop schedule was 7 1/2 to 9 weeks from plugs.

Postharvest Handling

Stems were harvested into water in the greenhouse when at least one floret per stem was open. The stems were sorted according to number of open flowers and stem caliper, recut to 18 inches, and placed in the appropriate treatments. Unless otherwise indicated, the floral solution used in all experiments was 72F deionized water (similar to distilled water). After treatment, stems were placed (one per vase) at 72F under approximately 100 footcandles for 12 hours per day at 40-60 percent relative humidity. Vase life was considered finished when open flowers were more than one-third dead or two-thirds wilted. There were usually a significant number of wilted flowers along with the minimum one-third dead flowers.

Postharvest Results

Vase life of ‘Vivas Blue’ stems averaged 11-12 days without any treatments, and the cultivars had rather simple needs in terms of postharvest. Floral holding and hydrating solutions and sugar pulses had little effect. Interestingly, while stock is often thought to be sensitive to ethylene, exogenous ethylene had no effect and neither did either of the anti-ethylene agents, STS and 1-MCP.
  
‘Vivas Blue’ not only tolerated cold storage well, but storing stems dry at 36F for one or two weeks actually increased vase life by one to three days. This trend showed up in two experiments and is quite surprising, considering that storage reduces the vase life of most cut flower species.
    
Another interesting finding was the effect of floral foam on cut stock stems. Many cut flower species are negatively affected by floral foam, which is why we include it in routine testing procedures.  Vase life of ‘Vivas Blue’ was increased by up to several days when floral foam was used. One reason could be that the foam reduced the pH of the vase solution.
    
Using either 2 or 4 percent sucrose in the vase water caused the flowers to turn much darker purple. The longest vase life occurred when we used 2 percent sucrose with floral foam. No commercial floral preservatives were trialed with foam, but they are likely to have a similar effect.

The authors thank Ingram McCall, Diane Mays, Emma Locke, Erin Possiel and Eric Olson for assisting in the production and harvest, and Roland Leatherwood for assisting in ethylene studies. We are very much appreciative of American Floral Endowment for funding the work and Sakata Seed America for providing the stock plugs.

John Dole

John Dole is Professor and Head of the Department of Horticultural Science at North Carolina State University. Contact him at [email protected]