Astilbe is a classic perennial that gives low-light areas a boost. Also known as false spirea, it provides the perfect punch of color for shade and even partial shade spots, though it is happiest in the deepest of shade. Astilbe is a gorgeous shade-loving perennial that produces upright, tight clusters of colorful blooms that open slowly to present feathery plumes. Contrasting nicely are its toothed, compound leaves that create a fern-like appearance.
Astilbe’s high impact flower spikes provide shady gardens with extended color from spring into autumn. It is eye catching at every stage of maturity, part of what makes it so appealing. The varietal color palette ranges from lilac and pinky-purple to magenta, apricot and garnet. Waxy foliage is often covered with a silver-lacey overlay.
Plants form attractive clumps or mounds and can grow as tall as 3 feet and stay as petite as just 12 inches. A tough, deer resistant choice that is not a favorite of rabbits, Astilbe is hardy in USDA Hardiness Zones 3-9. It is stunningly beautiful when used alone or in combinations in the landscape. In addition, its clusters often dry in place, and the dried plumes can last well into fall. Their durability and showiness also makes them great cut flowers.
The ‘Vision’ varieties showcase gorgeous bronze-green foliage contrasting with clear white, pink or raspberry purple plumes. These varieties are also some of the more sun tolerant in the class. The collection includes ‘Vision in White’, ‘Vision in Pink’, ‘Little Vision in Purple’, ‘Little Vision in Pink’ and ‘Little Vision in White’, each with its own benefits. ‘Vision in Pink’ requires less moisture than other varieties, while ‘Vision in White’ provides a more compact option.
‘Look at Me’ is one of our favorites, sporting an eye-catching combination of rich red stems that hold bubblegum pink flowers, while ‘Delft Lace’ displays soft apricot-pink blooms held high above foliage on candy apple red stems. ‘Erika’ features triangular-shaped plumes of clear pink flowers, and ‘Montgomery’ offers wine-red plumes that appear mid-summer. And of course no Astilbe article would be complete without the mention of ‘Sprite’, a Perennial Plant of the Year that is definitely worthy of consideration with its shell pink plumes and exceptionally petite habit.
Astilbe is an easy-growing, low-maintenance plant, as long as you understand its preferences. From a 38 liner planted into a 1-gallon pot, plants will finish for spring sales in approximately eight to 10 weeks. Maintain greenhouses at 65°-75°F for daytime and 55°-65°F at night.
Choose a well-draining commercial media. Astilbe prefers slightly acidic media, so aim for soil pH between 5.8 and 6.2. Maintain electrical conductivity (EC) at 1.8 to 2.2 mS/cm using the 2:1 extraction method. Above this, leach with clear water.
Grow plants evenly moist, and remember they are moisture lovers, so don’t let Astilbe dry out. If they do, foliage may turn up or become brown. This is a risk especially in times of intense heat or drought, making them unsalable. Still, avoid letting water stand on the foliage, or you risk crown and root rot.
Astilbe has moderate fertilization requirements and will not need fertilizer for the first few weeks, until active growth begins. Provide a constant liquid feed at low levels of 100 to 150 ppm nitrogen. Note that Astilbe does have some salt sensitivity, so monitor levels carefully.
Provide shade to partial shade. No more than 1,800 foot candles of light and probably closer to 1,000 foot candles is better. These long-day plants should not need supplemental lighting.
Astilbe benefits from plant growth regulators (PGRs) for consistency and to prevent too much stem elongation. After blooms appear, apply approximately 5,000 ppm of a PGR such as B-Nine. No pinching required.
Cold treatment is required for flowering in Astilbe. Plan to provide approximately 10 to 12 weeks of 41°F or less, depending on the cultivar. Remember to decrease irrigation to accommodate dormancy and die back.
Scout and monitor regularly for pests such as whiteflies and powdery mildew. A good preventive program is key. Maintain proper sanitation procedures, including humidity control and spacing for good air circulation (though pot to pot spacing is fine until growth extends past the pot edge). Consider a preventive fungicide drench at transplant and follow a monthly broad-spectrum fungicide control program.
Josiah Raymer is head grower and general manager for Emerald Coast Growers, one of the country’s largest liner producers. www.ecgrowers.com