Photo courtesy of Walters Gardens
Perennial growers are familiar with the genus Amsonia thanks to its many practical landscape uses. Amsonia easily fills space in the garden with a bushy, shrub-like habit and naturally blooms in late spring, making it perfect for retail sales. ‘Storm Cloud’ is a fantastic new cultivar, most noted for its incredibly dark emerging foliage and brilliant display of periwinkle blue flowers. A. ta bernaemontana types grow a little differently than the more popular A. hubrichtii , so here are some tips and tricks for success we’ve found in our trials.
For more: waltersgardens.com
Photo courtesy of Walters Gardens
Potting and Timing To grow the highest-quality finished plant, the best way is by starting a 72ct plug. Plant one plug per premium 1-gallon pot from late May to early July (in zone 6) and grow them outdoors for sale the following spring. Bury the crown slightly below the soil line to encourage eye development.
Amsonia can also be started from bare root, planting one root per trade 1-gallon pot in early spring. Bury the crown slightly below the soil line. Grow indoors at a cool temperature of 55-60° F and hold them at 40-50° F when finished. Allow 6-8 weeks finishing time.
Whether starting with plugs or bare root material, use a well-drained soil mix composed of bark and peat with a pH of 5.8-6.5.
Vernalization Amsonia requires vernalization to bloom, achieve its mature upright habit, and produce multiple stems per pot. 72ct plugs will need to go through a 10-12-week vernalization (at 40-50° F) in order to have blooming plants the following spring.
Cultural recommendations Fertility After new leaves emerge, use a water-soluble fertilizer at 50-100 ppm nitrogen constant liquid feed at every watering or incorporate slow release fertilizer at a medium rate. The recommended EC rate is 2.0-3.0 using the pour-through method.
Moisture Amsonia prefers moderate moisture and requires a well-drained potting media. Allow plants to dry between waterings.
Lighting Amsonia is daylength neutral and does not require artificial lighting to flower. However, high light levels are recommended during the growing season. This is a full sun plant.
Temperature Growing Temperature Grow Amsonia indoors from bare root at 55-60° F. Grow 72ct plugs outdoors under natural temperatures in summer. Do not force plants to bloom under warm temperatures or it will cause them to stretch. Forcing under cool 50-60° F temperatures will result in sturdier, more compact plants for retail. Overwintering The best way to overwinter Amsonia is in a minimally heated greenhouse kept slightly above freezing. They may also be overwintered outdoors under a heavy frost blanket or in an unheated greenhouse.
Finishing Pinching DO NOT PINCH an emerging Amsonia once they have been vernalized! Doing so will likely eliminate flower production that year. After flowering, it is appropriate to shear the plants back by half in midsummer to create a fuller habit.
PGRs After the plants are 4-5” tall, apply a uniconazole drench at 1 ppm. An additional spray may be necessary 7-10 days later.
