crop cultivation GGaillardia:aillardia: Unique Forcing Requirements Of Old And New

This article highlights the fl owering requirements of the vibrantly hued cultivars, which have recently reclaimed the limelight. Growers interested in successfully producing fl owering potted should keep reading. Figure 1. It is not uncommon to observe gaillardia planted alongside annuals because of their profuse and continuous fl owering, as seen here in the State University By Sonali Padhye, Catherine Whitman, trial gardens. Arthur Cameron and Erik Runkle

aillardia adorns its native and attractive fl ower color and form. Most 1). It won both the All American and Fleuro- North and South American commercially available perennial cultivars select awards in 2005. More recently, ‘Fanfare’, habitats and cultivated gar- of gaillardia, including some discussed here, with its cool tubular petals, and ‘Oranges and dens with daisy-like fl owers of have Gaillardia x grandifl ora in their genetic Lemons’, with its continuous yellow red and yellow, which resemble background. Although a short-lived perennial fl owers, have brought even more attention to Gvibrant-colored blankets created by American in the landscape, gaillardia continues to be this genus (Figure 2, below). Indians. Hence, gaillardia has been given the popular and is widely used in fl ower beds and common name of blanket fl ower. Gaillardia mixed containers. Cultivars consists of more than a dozen annual and In recent years, the introduction of excep- Hybridization between annual and peren- perennial species of which Gaillardia x gran- tional new cultivars has brought gaillardia nial species of gaillardia has yielded an array difl ora, a naturally occurring hybrid between back into the limelight. In 2003, gaillardia of cultivars with attractive colors and forms, and Gaillardia pulchella, has ‘Sundance Bicolor’ was awarded the All Amer- adaptability to diverse growing conditions, and been particularly popular in the past several ican Award. Gaillardia ‘ Sun’ is even an extended bloom season. The introduction years. This is at least in part due to its peren- more impressive and can be used alongside of genes from annual species has decreased nial life cycle; cold hardiness to USDA Zone annuals to provide an instant splash of color in the lifespan of several cultivars, making many 4; heat, humidity and draught tolerance; vigor; the garden with its non-stop fl owering (Figure selections short-lived perennials in the garden. However, genes from annual species also have contributed to the non-stop fl owering of many cultivars, attracting consumer interest. We have evaluated traditional gaillardia cultivars with red- and yellow-colored fl owers including ‘Goblin’, ‘Dazzler’, ‘Baby Cole’ and ‘Burgundy’. ‘Goblin’ has been rather popular over the years and requires vernalization treatment and long days for synchronized and complete fl owering. ‘Baby Cole’ is shorter, while ‘Dazzler’ is taller than ‘Goblin’. We’ve also experimented with newer red and yellow fl ower introductions, including ‘Arizona Sun’, ‘Galileo’ and ‘Gailarus’. As its name sug- gests, ‘Burgundy’ has maroon infl orescences. The color pallet of gaillardia has been broad- ened by the introduction of and apricot fl owers of ‘Oranges and Lemons’ and ‘Sum- Figure 2. Unique yellow-orange fl ower color of gaillardia ‘Orange and Lemons’ (left) and exceptional tubular petals of gaillardia mer’s Kiss’. ‘Fanfare’ has tubular ray fl owers ‘Fanfare’ (right). and is a favorite among consumers. ➧

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USDA Time Flower at 68° F Cold Starting Vernalization Photoperiod Weeks Weeks Hardiness Material Response for Flowering to VB to Flower Zone Comments

‘Arizona Sun’ 128-cell Facultative response. Facultative long day (LD) 3 after 15 5-6 after 15 3-8 Nice fl ower color and non-stop seedlings 15 weeks at 41° F hastened . Under LD, fl owering weeks of weeks cold fl owering in the garden. Variability fl owering by 2-3 weeks. was hastened and buds and cold & & under LD associated with seedlings was height were increased under LD observed. compared to short days (SD).

‘Dazzler’ 128-cell Unknown. All plants were Facultative LD plant. Faster 3-10 Fewer fl owers under SD. Plants seedlings cooled for 15 weeks. to fl ower, more fl owers, taller look similar to ‘Goblin’ but taller. under LD.

‘Gailarus’ Vegetative Facultative response. Facultative LD plant. Plants 5-7 after 6-7 after ≥6 During cooling, several cuttings Cooling for 3-15 weeks under SD were shorter, had ≥3 weeks at weeks at died in the cooler and at forcing hastened fl owering under SD. fewer buds and fl owered 41° F & LD 41° F & LD plants quality was poor for 2-3 Cooled plants had more later than LD plants. forcing forcing weeks. However, plants subse- fl ower buds under SD and LD. quently recovered. Flowers fairly similar to that of ‘Arizona Sun’.

‘Galileo’ Vegetative Facultative response under Obligate LD without 4-5.5 after 7-9.5 after Flowers have red centers like cuttings LD and obligate under SD. vernalization treatment and ≥3 weeks of ≥3 week ‘Gailarus’ but more yellow on the 3-15 weeks at 41° F facultative LD following cold & under cold & petal tips. ‘Galileo’ rooted more hastened fl owering under SD. vernalization treatment. LD under LD easily and responded more ≥3 weeks at 41° F recom- After 15 weeks at 41 °F, strongly to photoperiod and mended for LD force. fl owering under SD was vernalization treatments than incomplete and delayed. ‘Gailarus’.

Table 1. Research-based production information and fl owering characteristics for select gaillardia cultivars.

Our fl oriculture research group at Michigan the fl owering of many gaillardia cultivars requires is essential to consider its specifi c forcing require- State University (MSU) has performed research exposure to low temperature, also known as ver- ments. Additionally, starting material often has a to identify the fl owering requirements of several nalization treatment, as well as exposure to a long signifi cant impact on vigor and fl owering time new and old gaillardia cultivars. This article photoperiod. During our experiments, we have and therefore should also be considered prior to highlights our fi ndings and provides infor- recorded signifi cant differences in vernalization forcing. mation for successful production of fl owering and photoperiodic requirements of gaillardia potted gaillardia. cultivars (Table 1). Hence, to successfully force a Propagation Like many temperate herbaceous perennials, gaillardia cultivar for a scheduled market date, it Depending on the cultivar, gaillardia can be

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USDA Time Flower at 68 °F Cold Starting Vernalization Photoperiod Weeks Weeks Hardiness Cultivar Material Response for Flowering to VB to Flower Zone Comments

‘Goblin’ Seed. Facultative response. Facultative LD plant. Plants 3 6.5 4-8 Traditional cultivar that has large Juvenility Vernalization treatment fl owered without cold but and showy red fl owers with yellow ends with increased fl owering percentage were slower to fl ower, had rings. Can be highly variable in ~16 nodes and uniformity and hastened fewer fl owers and were form and fl owering. Deadheading (leaves) fl owering. 9-12 weeks at 41° F shorter. is benefi cial in the garden for is recommended. Some plants continuous bloom. fl owered without a cooling treatment.

‘Fanfare’ Tissue No response. Facultative LD. Flowering time 1-2 5-6 4-9 Very showy plants bloom culture was similar under SD and LD non-stop in pots and gardens. but more buds under LD. Seed-heads are quite attractive and dead-heading not required for re-blooming.

‘Oranges Vegetative No response. Facultative LD. Flowering 3-4 4.5-6 6-10 Very unique yellow-orange fl ower and Lemons’ cuttings slightly delayed under SD and color. Plants fl ower non-stop in the plants shorter with fewer buds garden and in containers. Seed under SD. heads are attractive and dead- heading not required for re-blooming.

Table 1. (continued) propagated by seed, shoot-tip cuttings, division fl owering time when plants were forced under long days, stock plants fl ower and thus cut- or tissue culture. Similar to many other herba- a 9-hour photoperiod, while a 16-hour photope- tings are reproductive. Under short days, few ceous perennials, seed-propagated cultivars riod induced more uniform fl owering. cuttings are produced because plants remain such as ‘Goblin’ and ‘Arizona Sun’ were more Although vegetatively propagated gaillardia as a rosette. Also, liners that are rooted and variable in their fl owers and fl owering compared cultivars are more uniform than seedlings, a bulked under long photoperiods can fl ower to vegetatively propagated cultivars such as potential challenge with them can be main- sporadically in the plug tray. ‘Fanfare’ and ‘Gailarus’. In some cultivars, pro- taining vegetative stock plants and liners until viding inductive treatments such as long days forcing begins. This is particularly an issue Juvenility and Bulking may reduce (but not eliminate) the variability in with continuously fl owering cultivars such as During the juvenile phase, seedlings remain fl owering time associated with seedlings. For ‘Oranges and Lemons’ that generally do not vegetative and do not respond to inductive example ‘Arizona Sun’ was highly variable in require vernalization for fl owering. Under treatments such as vernalization or long ➧

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important to allow plants to bulk up to size prior Gaillardia ‘Arizona Sun’ to forcing. Also, if some of the plugs have fl ower 0 weeks at 41° F 15 weeks at 41° F buds upon receipt, their removal prior to bulking 11 weeks forcing at 68° F 6 weeks forcing at 68° F is benefi cial to ensure synchronized fl owering.

Vernalization Vernalization is defi ned as the promotion of fl owering following a cold treatment. The cooling treatment itself is sometimes called a vernalization treatment. Some cultivars require vernalization for fl owering and thus have an obligate vernalization response. Other cultivars have a facultative vernalization response, where vernalization can accelerate fl owering, improve fl owering characteristics SD LD-INC LD-HPS SD LD-INC LD-HPS such as higher fl owering percentage, synchro- nize fl owering and increase fl ower number. Figure 3. Gaillardia ‘Arizona Sun’ had a facultative vernalization response when cooled at 41° F for 15 weeks. Flowering was The vernalization response of gaillardia is hastened by 6-7 weeks when vernalized plants were forced under a short day (SD, 9 hours), while when forced under long days (16 hours) provided by incandescent lamps (LD-INC) or high-pressure sodium lamps (LD-HPS), vernalized plants fl owered 2-3 weeks highly cultivar-dependent and ranges from no earlier than non-vernalized plants. response to an obligate response, depending on the photoperiod (Table 1, pages 22 and 23). photoperiods. Typically, plants become mature For example, a 15-week vernalization treat- and capable of fl owering once they have grown ment at 41° F did not infl uence the fl owering a certain number of leaves. This number time or fl owering characteristics of ‘Fanfare’ varies among species and cultivars. For example, and ‘Oranges and Lemons’. In contrast, ‘Ari- research at MSU found that the juvenile phase zona Sun’, ‘Gailarus’, and ‘Goblin’ exhibited a of ‘Goblin’ ends after the plant has unfolded facultative response, and their fl owering was about 16 leaves. Hence, ‘Goblin’ seedlings need accelerated by a vernalization treatment. ‘Gal- to be bulked under short photoperiods until at ileo’ required vernalization to fl ower when least 16 leaves are present prior to providing forced under a 9-hour photoperiod and had a vernalization or photoperiod treatments. In our facultative vernalization response when forced evaluations, ‘Arizona Sun’ seedlings had more under a 16-hour photoperiod. than 10 leaves upon receipt. Therefore, it did In many cultivars, the magnitude of accel- Figure 4. The critical photoperiod of gaillardia ‘Goblin’ is not exhibit juvenility and fl owered uniformly eration of fl owering by a vernalization treat- between 12 and 13 hours. Note that the fl owering percentage when provided with a vernalization treatment ment depended on the forcing photoperiod. For reported in the fi gure was recorded when the photograph was taken. More plants eventually fl owered. Plant height at fl ow- followed by long days. instance, a vernalization treatment at 41° F for ering generally increased with photoperiod. To maintain the aesthetic appeal of gaillardia 15 weeks hastened fl owering of ‘Arizona Sun’ produced for large-sized fi nal containers, it is by 2-3 weeks when forced under a 16-hour ➧

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photoperiod at 68° F, but when plants were forcing gaillardia, plants tend to stretch under Gaillardia forced under a 9-hour photoperiod, vernaliza- incandescent lamps and hence, may require ‘Oranges and Lemons’ tion hastened fl owering by 6-7 weeks (Figure more liberal use of plant growth regulators to 0 weeks at 41° F 3, page 24). control stem extension. 6 weeks forcing at 68° F

Percent Flowering Photoperiod Light Quantity 100 100 100 Similar to many photoperiodic herbaceous Gaillardia is a sun-loving perennial and perennials from temperate origins, most gail- becomes rather fl oppy when grown under lardia cultivars are long-day plants and fl ower shade in the garden. Similarly, gaillardia when the photoperiod exceeds a critical value, thrives under high light in the greenhouse and typically 12-13 hours (Figure 4, page 24). Gail- produces weaker stems when grown under lardia typically respond facultatively to long lower light. When provided with supplemental days and fl ower faster and/or have improved light, gaillardia cultivars were more compact fl owering characteristics when forced under and produced more branches and fl owers in long days, including more uniform fl owering, our trials (Figure 5). To produce high-quality increased fl owering percentage, and more gaillardia, the average daily light integral in fl owers and fl owering laterals. the greenhouse should exceed 10 mol·m−2·d−1. Although many cultivars do eventually fl ower when grown under short days, the Regulating Plant Growth plants are excessively compact and form Many gaillardia cultivars are unruly and SD LD-INC LD-HPS rosettes with few fl owers (Figure 5, left). There- fl oppy when grown under low light levels, fore, we consider most gaillardia to be obligate and plants elongate excessively when long day Figure 5. Although gaillardia ‘Oranges and Lemons’ fl ow- long-day plants and recommend a photope- lighting is provided by incandescent lamps. ered completely under short days (SD) or long days (LD), riod greater than 13 hours during forcing. To Among various factors to consider for plant plants under SD formed rosettes and had fewer fl owers and achieve this, long-day lighting is required in growth regulation of gaillardia, cultivar selec- branches. Hence, horticulturally ‘Oranges and Lemons’ can North America from mid-September through tion is of particular importance. In our trials, be considered a LD plant. Note that plants grown under early April. Long-day lighting can be provided high-pressure sodium lamps (LD-HPS) were more compact ‘Gailarus’ and ‘Galileo’ were appropriate for and had more branches and buds than those under incan- as a 4-hour night interruption or day exten- 5½-inch containers when forced without plant descent lamps (LD-INC). sion. When providing long day lighting for growth regulator applications (Figure 6, oppo-

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sion. Sumagic also was effective in controlling Arthur Cameron is professor and Erik Runkle is the height of ‘Fanfare’. We recommend growers associate professor and fl oriculture extension conduct their own trials to determine effective specialist in the Department of Horticulture, plant growth regulator rates for their growing Michigan State University, East Lansing, Mich. conditions and use graphical tracking to deter- Padhye can be reached at [email protected]. mine application time.

Summary Gaillardia cultivars comprise a group of The authors would like to thank the Metropolitan great garden plants and can be used in com- Detroit Flower Growers Association and the Western bination with annuals and perennials for non- Michigan Greenhouse Association for fi nancial sup- stop color through the summer. Similar to port. We express our appreciation to C. Raker and Sons, ‘Gailarus’ ‘Galileo’ their fl ower colors and forms, the regulation Oro Farms, and Walter’s Gardens for donations of plant Figure 6. Gaillardia ‘Gailarus’ and ‘Galileo’ were compact of fl owering varies among Gaillardia culti- material, Michigan Grower Products for donations of and suitable for 5½ inch containers when forced without plant vars. ‘Goblin’ and ‘Arizona Sun’ facultatively media, and The Blackmore Co. for fertilizer donations. growth regulator applications. respond to a vernalization treatment, whereas We also thank Mike Olrich and undergraduate student ‘Oranges and Lemons’ and ‘Fanfare’ do not employees in the Floriculture Program at Michigan State site). In contrast, ‘Oranges and Lemons’ was too require vernalization. Most gaillardia culti- University for providing plant care. tall for 5½-inch containers when grown under vars are horticulturally long-day plants, and a 16-hour photoperiod provided by incandes- thus a photoperiod longer than 13 hours is rec- cent lamps (Figure 5). ommended for rapid and uniform fl owering. We have tested the effects of 100 ppm of A- We’ve been impressed with the new intro- Rest (ancymidol), 5,000 ppm of B-Nine (dami- ductions of gaillardia and anticipate more LearnMore For more information related nozide), 90 ppm of Bonzi (paclobutrazol), 1,500 exciting introductions from breeders in the to this article, go to www.gpnmag.com/lm.cfm/gp090701 ppm of Cycocel (chlormequat chloride) and 15 near future. GPN Reader Interest Review ppm of Sumagic (uniconazole) as foliar sprays Please write in the appropriate number on height control of ‘Burgundy’. A-Rest was on the Reader Service Card to indicate slightly effective, and B-Nine and Sumagic Sonali Padhye is post-doctoral research asso- your level of interest in this article. High 1500 Medium 1501 Low 1502 were highly effective at inhibiting stem exten- ciate, Catherine Whitman is research technician,

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