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perennial solutions Primula acaulis Harlequin Series

Breeding efforts throughout the past few decades have helped produce primula varieties with improved attributes, such as those in the Harlequin series.

he true arrival of spring is annuals. The Harlequin series can the Harlequin series will finish the frequently welcomed by be grown successfully in warmer plug stage in approximately 8-10 the vivid colors of the zones when adequate shade and weeks. Fertilizers are usually applied By Paul Pilon TEnglish primrose. Primula moisture is provided. once the true leaves are present. are widely grown and marketed as Apply 75- to 100-ppm nitrogen every bedding plants, potted house plants Propagation third irrigation or 50 ppm every irri- and perennials. Although they make Harlequin seeds are commonly gation using a balanced water-solu- excellent garden plantings, they are sown in open flats or plug trays filled ble source. Maintain a 5.5-6.2 pH. widely underutilized in North with a fine-textured peat mix with a Primula are sensitive to high light American landscapes. Historically, low nutrient charge (EC less than levels. To prevent leaves from burn- primula were difficult to commer- 0.75). The seeds require light for ger- ing, provide 30- to 50-percent shade cially produce, were short lived in mination, and covering them with when natural light levels exceed the landscape and had a limited germination mix or vermiculite fol- 3,000 foot-candles range of garden colors available, but lowing sowing is generally not rec- breeding programs throughout the ommended. During germination, Production last 20-30 years have greatly maintain moderate moisture levels, The Harlequin series is most improved its attributes. never allowing the seed to dry out or commonly produced in small con- The Harlequin series, exclusively become saturated. If it is difficult to tainers, such as 4- to 5-inch pots, available from S&G Flowers, is the maintain moisture around the seed with a single plug planted in a pot’s result of such breeding efforts. This during germination, a very light cov- center. To prevent sunscald, primula series produces a stunning display of ering of #2 course-grade vermiculite should not be produced at light lev- bicolor flower clusters held closely will help maintain sufficient moisture els greater than 3,000 foot-candles. above compact rosette foliage. Five around seeds. When a light covering colors are currently being offered: is applied, provide at least 50 foot- Blue Bicolor (midblue margin with candles of supplemental light during white center), Carmine Bicolor (dark the germination process. carmine red/rose margin with white It is best to keep temperatures center), Red Bicolor (bright scarlet- cool (59-65° F) during germination red margin with yellow center), Rose to improve crop uniformity and Bicolor (rose margin with white cen- prevent early elongation. Avoid ter) and Bicolor Mix (a mixture of germination temperatures greater bicolors and solids). All varieties than 68° F. Starting primula inside a have the characteristic yellow eye. germination chamber will help This is an early to mid-flowering maintain cool temperatures, series that is well suited for produc- increase both the germination rate tion in small containers or in combi- and percent germination, and nation with other plants in color decrease the time necessary for all bowls or patio planters. the seeds to sprout. At these temp- Primrose are delicate, cool-sea- eratures, seeds should be germinated son perennials that perform best in in 7-10 days. shady locations across much of Once germinated, they can be USDA Hardiness Zones 4-7. Like grown with temperatures from 60 to many cool-season plants, primula 65° F. Following germination, reduce do not tolerate the extreme summer moisture levels somewhat, allowing heat of much of the United States or the growing medium to dry out the severe northern winters. In these slightly before watering to help pro- This series produces a stunning display of bicolor flower clusters held closely above compact rosette areas, primula are often treated as mote rooting. At these temperatures, foliage. (Photos: S&G Flowers)

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Primula perform best when els (greater than 1.5 EC) and overly release fertilizers incorporated at a grown in a moist, well-drained dry growing conditions. Growers rate equivalent to one-half to three- medium with a slightly acidic pH: commonly deliver nutrients using fourths lb. of nitrogen per yard of 5.5-6.0. They are light feeders; pro- nitrate-nitrogen water-soluble fertil- growing medium to deliver nutri- viding moderate to high fertility izer formulations containing calci- ents to primula crops. levels (particularly from ammoni- um and potassium nitrates, feeding Foliage yellowing may occur um sources) causes them to appear at rates of 100-ppm nitrates. during production; this yellowing is lush and leafy. Avoid high salt lev- Growers may also use controlled- an indication of either low overall

Varieties in the primula Harlequin series are easy to force into bloom and are most commonly produced for early spring sales.

nutrient levels or high pH (iron deficiency). Conduct periodic soil tests to monitor and help maintain adequate pH and soluble salt levels. When irrigation is necessary, water thoroughly then allow the soil to dry slightly between waterings. The Harlequin series has a natu- rally compact growth habit and will usually not require plant growth regulators (PGRs) to control plant height. Under certain growing condi- tions or under high plant densities, it may be necessary, although not com- LEARN, GROW & BE INSPIRED mon, to use chemical PGRs. I have used Concise or Sumagic (unicona- zole) at low rates (2-3 ppm) to darken 1,400 Exhibit Spaces primula foliage prior to shipping rather than to reduce plant height. 120 Educational Sessions 1,000s of Business Solutions Insects And Diseases English primroses can generally July 14–17, 2007 be grown insect and plant-pathogen Columbus, Ohio free. Occasionally, aphids, leafhop- pers, slugs, spider mites, thrips and whiteflies may appear and cause www.ofa.org only a minimal amount of crop 614-487-1117 injury. The primary diseases grow- ers should watch for are Botrytis, powdery mildew and Ramularia leaf spot (yellow spots on leaves that turn brown). Reducing the presence of free- standing water on leaves, lowering the relative humidity levels and providing adequate air circulation can decrease the occurrence of Ramularia. Several fungicides are labeled and effective at controlling this disease, including Daconil (chlorothalonil), Milstop (potassi- um bicarbonate) and 3336 (thio- phanate methyl). Growers should have routine scouting programs in place to detect the presence of insects and diseases early and determine if and when control strategies are necessary.

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Forcing acquired from many reputable Paul Pilon is president of Perennial management, weed control, prop- Solutions Consulting, Jenison, agation, forcing, plant growth regu- Varieties in the primula Har- perennial plug producers or Mich., and author of Perennial lators, overwintering, and individual GPN lequin series are easy to force into plant brokers. Solutions: A Grower’s Guide To cultural programs and schedules for bloom and are most commonly pro- Perennial Production. The book is many of today's most popular peren- duced for early spring sales. Primula a guide to propagation and grow- nial species. Pilon can be reached at LearnMore ing containerized perennials (616) 366-8588 or paul@perennial- can be forced into bloom using the For more information with chapters on media, fertil- solutions.com. Get a copy of his book at related to this article, go to traditional method, which entails ization, insect and disease www.perennial-solutions.com. sowing seeds in early summer, pro- www.gpnmag.com/lm.cfm/gp030706 viding a cold period during winter months and forcing them into bloom in the early spring or using methods to achieve first-year flowering. With either method, the plugs are physio- logically mature enough to initiate flower buds when they are at the 6-10 leaf stage (approximately 12-16 weeks after sowing). Generally, flower buds can be observed deep in the crown of the plant when the leaves reach the edge of a 4-inch container. To produce flowering English primroses using traditional methods, growers practice the following guidelines. The seeds are typically sown in the late spring to early summer. The plugs are transplanted into the final containers during the late summer to early fall (8-10 weeks after sowing). The plants are exposed to at least six weeks of tem- peratures below 45° F during the winter months. After flower buds are visible in the late winter, they can be grown at 50-60° F for 3-5 weeks to produce flowering plants. As mentioned above, young prim- ula plants with 6-10 leaves are mature enough to initiate flower buds. They are classified as faculta- tive long day and irradiant plants. Under long-day conditions (day lengths more than 14 hours) and Floramite controls mite pests when grown under amble light levels (1,500-1,700 foot-candles), primula in all life stages. will initiate flowers faster than when Make Floramite® SC miticide the cornerstone of your mite produced under lesser conditions. control program. A single application stops tough two-spotted Once the plants are well estab- spider mites, from eggs to adults. Floramite miticide delivers lished (3-6 weeks after potting), more than 28 days of residual control. Its unique mode of they can be grown at 55° F and action and highly selective activity goes easy on predacious long days with ample light intensi- mites and beneficial insects to help extend your IPM program. ty to promote rapid flower induc- Safe on ornamentals and bedding plants, Floramite is tion and uniform flowering. Most economical and user-friendly. Ask your chemical supplier growers provide at least six weeks for Floramite, the one that controls spider mites in all life of vernalization at 45° F in lieu of stages - the one for all. the long-day treatment. After the flower buds have been initiated (visible bud), they can be pro- duced at 50-60° F at natural pho- toperiods for an additional 3-5 weeks until they flower. With this method, it takes 11-13 weeks to www.chemtura.com reach flowering from the time Always read and follow label directions. plugs are transplanted. Floramite is a registered trademark of a subsidiary of Chemtura Corporation. ©2005 Chemtura Corporation Availability FL-ad01-0705 CCP-10905 Primula Harlequin series seed is exclusively available to growers through S&G Flowers (www.sg- flowers-us.com). Plugs can be

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