Green Guides: Penstemon 'Sweet Joanne'

Use ‘Sweet Joanne’ in a border or as an accent plant.Since the early 1990s, horticulturists at the University of Nebraska’s West Central Research and Extension Center have been crossing penstemon plants and assessing the progeny. ‘Sweet Joanne,’ selected by horticulture professor Dale Lindgren, was named after his wife.
 
‘Sweet Joanne’ is one of more than 25 selections of ornamental plants for which Lindgren has been responsible. His penstemon ‘Husker Red’ was selected as the 1996 Perennial Plant of the Year.
 
‘Sweet Joanne,’ which is part of the Blooms of Bressingham line, combines the best attributes of its genus. Plants produce large lavender-pink trumpet flowers with white throats and bright magenta veins. ‘Sweet Joanne’ flowers heavily and continuously from late May through June and will rebloom in fall if spent flower stems are removed.
 
Plants are vigorous and form dense clumps that increase in size each year. ‘Sweet Joanne’ does best in full sun and grows to 24 inches tall and wide. Plants, which exhibit extreme tolerance to insects and diseases, are hardy in USDA Hardiness Zones 5-9.
 
Its medium height makes it suitable for a border or accent plant. It offers a very long life compared to other penstemon selections, Lindgren said. 
 
“There are similar varieties out there, but this one is extremely hardy,” Lindgren said. “It continues to flower until frost and has shown 100 percent survival over the winter season.”

Propagation
‘Sweet Joanne’ can only be propagated by licensed propagators. For unrooted cuttings, propagation usually takes two to three weeks, with an additional four to five weeks to produce a finished liner. Total production time for a finished liner is seven to eight weeks (usually faster in the summer).
 
Transplant 72-cell rooted liners into 6- or 8-inch or standard 1-gallon pots with one cell per pot. For larger pots, use two or more liners.
 
Use a porous, well-draining growing medium with a pH of 5.5-6.5. Plants should be grown moist and will require more water once established. While actively growing, apply a constant liquid feed of 100-150 parts per million nitrogen.
 
Supplemental lighting is not required when plants are finished during the natural season. It is recommended to grow the plants outdoors to minimize the amount of stem stretch. Best growing-on temperature range is 65°F-75°F during the day and 60°F-65°F at night. Vernalization does not impact flowering.
 
If plants are being grown from unrooted cuttings, pinch the plants once while in the cell flat. Otherwise, no pinch is necessary.
 
Crop production time for rooted liners planted in 6-, 8-inch or 1-gallon pots outdoors in April to finished flowering plants is 10 weeks. Finishing time from unrooted cuttings to flowering plants is 17-18 weeks.
 
The only insect problem can be with spider mites. It doesn’t have any major disease concerns. 
 
For more: Blooms of Bressingham, (800) 321-9573; www.bloomsofbressingham.com.