Guide to Successful Outdoor Aster Production 6/98 HIL-505 Robert T. Eddy1 Brian E. Whipker Floriculture Extension Specialist

Most garden asters are cultivated varieties of the fall-blooming wildflower, Aster novi-belgii, or Michaelmas daisy. They are native to the United States and can be seen blooming along roadsides during the fall. From the wild types, Danish breeders have selected for new colors and compact shape. As a floriculture crop, they can be grown for cut flowers, an indoor pot crop in four-inch or 6-inch pots, or an outdoor perennial in 6-inch pots or larger. This leaflet covers the commercial production requirements for perennial garden asters.

Keys to Success with Garden Asters (these items will be highlighted in a summary box)

1. Plant cuttings upon arrival.
2. Start the crop 2 weeks later than mums.
3. Provide sufficient water.
4. Manage your fertility program.
5. Space plants for proper growth and good air circulation.
6. Pinch plants and apply plant growth regulators to control plant height.

Schedule

Garden asters flower under short days similar to mums and they can be grown on a schedule similar to garden mums. Grown under natural days, they flower 1 to 2 weeks earlier than garden mums. The earliest cultivars are ready to sell in mid- to late-August. Later varieties flower throughout September. They can be grown any time of the year by manipulating photoperiod. In general, asters are kept vegetative using long days (>14-16 hours of daylight) until size is achieved, then forced into flower with short days (Schwabe, 1985). Very short days will induce dormancy. Therefore, if growers are going to use shadecloth to induce earlier flowering, daylengths <10 hours should be avoided to prevent dormancy and the resulting bud abortion.

Flowering can be delayed with a combination of high temperatures, averaging over 68 oF, and high light. The flowering of an outdoor crop can be influenced by summer temperatures. Asters can be planted at the same schedule, size of pot, and medium as used for garden mums. They can also be planted up to 2 weeks later than a garden mum crop grown under similar conditions, because they produce an abundance of growth just prior to flowering. Rooted cuttings planted at the beginning of June may require a 1-1/2 gal container; mid-June an 8-inch container; July a 6-inch container for "fast-cropping". These later plants will require less pinching and perhaps more cuttings per pot. Experiments by Eddy and Hammer (1998) produced acceptable sized plants with one rooted cutting per 8-inch pot when planted on June 9.

Pinching

Pinch 7 to 14 days after potting rooted cuttings, removing all but 3 to 5 internodes. Pinch every 14 to 18 days until July 25, again leaving 3 to 5 internodes on each branch which has emerged since the previous pinch. Shears can be used. For a crop planted around June 9, 3 pinches are required.

Plant Growth Regulators

A plant growth regulator should be applied after the final pinch, when 1-1/2 to 2 inches of new growth has occurred. This will reduce plant height, intensify the dark green color of the foliage, and most importantly create rounder, more uniform plants. Foliar sprays of either B-Nine (two applications at 5000 ppm, applied one week apart) or Sumagic (a single application at 80 ppm) produced rounder, more uniform plants (Eddy and Hammer, 1998). Other recommendations include B-Nine at 1500 to 2000 ppm applied as needed (Luczai, 1992) or two applications of B-Nine at 2500 ppm (McAvoy, 1993).

Fertilization and Irrigation

Maintain the root medium pH between 5.8 to 6.5 for a soilless medium. Use a complete N-P-K fertilizer providing 200 ppm N and K via irrigation water. A rate of 150 ppm N and K may be sufficient for a soil-based medium. Asters are less salt-tolerant than mums. Excessive fertilization causes the plants to grow large and tilt in the pots. Growers need to manage their fertility program to avoid excessive EC build-up or monthly leaching of salts should be practiced. Low fertilization results in small plants. Fertilization outdoors may need to be supplemented with a higher rate or a slow release fertilizer like Nitroform (38-0-0) if excessive leaching occurs due to heavy rains. Though asters are more drought tolerant than garden mums, drought stress can cause yellowing of the lower leaves. Fertilization should be terminated when the flowers begin to open to improve flowering longevity. Foliar analysis values for garden aster are provided in Table 1.

Table 1. Foliar tissue standards for Garden Asters.
Nutrient	Recommended concentration
Nitrogen (N) (%)	2.2 to 3.1
Phosphorus (P) (%)	0.24 to 0.65
Potassium (K) (%)	3.3 to 3.7
Calcium (Ca) (%)	0.98 to 1.7
Magnesium (Mg) (%)	0.18 to 0.35
Boron (B) (ppm)	37 to 46
Iron (Fe) (ppm)	162 to 180
Manganese (Mn) (ppm)	65 to 273
Zinc (Zn) (ppm)	26 to 121
Values are reported on a dry-weight basis, based on a limited number of plants. The most recently matured leaves of field-grown plants were sampled when flower buds were present, but prior to flowering. Samples were taken from vigorously growing healthy plants and are only guidelines. Source: Armitage, 1993.

Spacing

Use the same spacing as for garden mums -- 18-inch centers for a 6-inch to 8-inch pot.

Insects

Asters have few insect pests. If needed, follow the same insecticide regime as for garden mums. Bees are attracted to aster flowers. Market the plants when one-quarter of the blossoms are open to prevent problems with attracting bees.

Diseases

Rust and powdery mildew are the two major foliar diseases of garden asters. Other possible foliar diseases are downy mildew, Alternaria spp. Cercospora asterata, and Septoria spp. Cultural practices to control foliar disease include avoiding wet foliage during irrigations and select a production site that provides adequate air circulation. Fungicides registered for Rust include: Dithane M-45WP, Bayleton or Strike 25DF, and Triforine 18EC; and for Powdery Mildew are: Karathane 19.5WP, Zyban 75WP, Bayleton or Strike 25DF, and Triforine 18EC. Read the label for use recommendations when applying these chemicals for disease control of asters. Potential root/stem diseases include Pythium, Phytopthera, Fusarium, Rhizoctonia, and Verticillium.

Future Considerations

Garden asters are extremely hardy. Given this fact, future follow-up sales may be limited. In addition, once established in the yard, garden asters are aggressive growers and some cultivars like Blue Butterfly may require up to 6 ft² of space.

Varieties

Make a majority of your order blue, red, and purple. The top selling varieties for Yoder are: Patricia Ballard, Frida Ballard, Professor Kippenberg #2, Celeste, and Winston Churchill. Table 2 contains additional growth information about the top 5 varieties.

Table 2. Descriptive information about the top 5 garden aster cultivars from Yoders.
Variety	Color	Vigor	Flower Size	Natural Response	Response Group (weeks)	Comments
Celeste	Lavender/ Blue	Medium	Medium	Early	5-1/2	A striking, dark-blue petaled flower with complementary yellow disk.
Frida Ballard	Raspberry	Medium	Medium	Mid	5	Very close in performance to Winston Churchill, except slightly darker color and later.
Patrica Ballard	Pink	Medium	Large	Mid	5	Large, lavender-pink flowers and moderate vigor. Avoid blackclothing for >10 to 12 hours for best bud set.
Professor Kippenberg #2	Lavender/ Blue	Short	Large	Mid	NR	Dwarf variety, with large- blue-purple flowers.
Winston Churchill	Raspberry	Medium	Large	Early	5	Top selling variety for Yoders.

Marketing

Garden asters provide another flowering crop to boost your fall sales. Along with garden mums, ornamental cabbage and kale, pansies, and other cool season annuals, garden asters can complete your product line. Though they can be grown on a schedule similar to garden mums, they are a new crop and should have their special features promoted.

• New Product: There is always excitement over something new. Your competitors probably won't have them either.
• New Colors: Blue has never been achieved in a garden mum, so this color is sure to draw attention, as will the bold, red varieties.
• Late Blooming: Color holds up into November on some varieties.
• Unique Habit: Few varieties achieve the perfect globe shape, but customers may like their natural, "wildflower" appearance.
• Perennial: You can guarantee it as a winter-hardy plant.
• Companion to Mums: The smaller, daintier aster flowers are an excellent complement to large mum blossoms. Blue varieties go well with yellow mums; pink varieties with lavender mums; purple with white mums.
• Cut Flower: Stems can be used as a cut flower. Harvest the stems when at least 20% of the flowers have opened and pollen is visible.

Recommendations

Make room for 100-200 garden asters for the fall. Often there are minimum order requirements, so consider pooling your order with another grower. Make a majority of your order blue, red, and purple. Pot them up 2 weeks after your mums and grow them on the same schedule. Purchase large, colorful care tags and a promotional kit if you retail. Plant some display beds containing garden asters and garden mums to promote asters and let consumers know what landscape design possibilities can be done with them.

For Further Reading

• Armitage, A.M. 1993. Aster, p. 168-172. In: Specialty cut flowers. Timber Press, Portland, Oregon.
• Eddy, R.T. and P.H. Hammer. 1998. Height control of garden aster with chemical growth retardants. Submitted to HortTechnology.
• Humm, B. 1997. Aster answers: pot crop success. GrowerTalks 60(14):55.
• Luczai, R. 1992. Garden asters: popular in the European market as a potted plant. PPGA News 23(8):20-21.
• McAvoy, R. 1993. Growing garden asters. Connecticut Greenhouse Newsletter (174):13-16.
• Schwabe, W.W. 1985. Aster novi-belgii, p. 29-41. In: A.H. Halevy (ed.), The handbook of flowering, vol. 5. CRC Press, Boca Raton, FL.

¹ Former graduate assistant

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