You can plant astilbe in either spring or fall but avoid planting in the hottest part of summer. If you must plant then, keep the plant well watered until new growth emerges. These are relatively slow-growing plants, but once established will bloom for many years before needing division. In hot, dry climates, they need to be planted in the shade and/or given plenty of water. Different varieties will bloom anywhere from mid-spring to late summer. If you plant different types of astilbe, you can prolong the bloom almost all season. The plumes remain in flower for several weeks and continue to look good as they fade and dry on the plant. No deadheading is needed since they will not bloom again.
Light
Astilbe plants grow best in part shade but can also grow in full sun or full shade. Astilbe will bloom in full shade, but the plants prefer some sunlight to achieve their full size. In hot weather and dry soils, the foliage will burn in full sun; here, some relief from the afternoon sun is mandatory.
Soil
Astilbe plants prefer fairly rich, moist soil, with a slightly acidic soil pH of around 6.0.
Water
The warmer the weather, the more moisture astilbe plants need, especially when situated in full sun. They do not handle prolonged periods of drought well; the leaves will brown and dry, and if left dry too long, the plants will die. In the absence of rain, water astilbe weekly and deeply at the base, avoiding overhead watering. Keep the soil moist but not soggy.
Temperature and Humidity
Astilbe plants are tough and hardy plants that can survive winter, even in harsh climates. After the first hard frost, put down 2 inches of mulch around the stem to protect the roots. Astilbe can grow in a moderately humid climate but in humid weather conditions, it can develop powdery mildew.
Fertilizer
Astilbe plants need phosphorus to bloom, so choose a fertilizer with the makeup of 5-10-5 or 10-10-10. Rake the fertilizer into the soil two weeks before you plant, or sprinkle a few granules onto the soil after the astilbe has been planted. Once the plant is established, fertilize every spring when the soil is moist. Apply the fertilizer on the soil and avoid getting any on the leaves, especially when they are wet, as the fertilizer will stick to them.
Types of Astilbe
There are new varieties introduced every year and recently, newer breeds with darker foliage. Some established standards include:
Astilbe x arendsii ‘Bridal Veil’: Mid- to late-season bloomer with full white plumes A. x arendsii ‘Fanal’: Blooms early with blood-red flowers on bronze foliage A. x arendsii ‘Rheinland’: Another early bloomer in a rich pink; very hardy A. chinensis taquetii ‘Purple Candles’: Deep purple, chenille-like plumes A. chinensis ‘Visions in Red’: Compact plant with bronze foliage and deep red flowers
Pruning
Little maintenance is required of astilbe plants. The flower heads will dry on the plant and remain attractive for many months. The flowers can be cut whenever they start to look ragged, or left up for winter interest and cut back in the spring.
Propagating Astilbe
Divide astilbe plants every four to five years to keep the plants healthy. In ideal conditions, astilbe plants can grow quickly and require more frequent division. Astilbe seed is available, but it can be difficult to germinate. It’s easiest to start with a plant or division. Even a small plant will quickly fill out and perform well in its first year.
Common Pests & Plant Diseases
Astilbes are virtually trouble-free, bothered by few diseases or insects. The tender, new growth may be nibbled on by groundhogs or rabbits, but once the plants have filled out, they typically don’t suffer any long-term damage.
