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Astilbe is a beautiful perennial plant that is known for its feathery plumes of flowers. To grow astilbe, choose a shady spot in your garden with moist, well-draining soil. Plant the astilbe in the spring, making sure to keep the roots moist. Water the plant regularly, especially during dry periods. Mulch around the base of the plant to help retain moisture and suppress weeds. Astilbe prefers acidic soil, so you may need to amend your soil if it is alkaline. Deadhead the flowers to encourage more blooms and divide the plant every few years to prevent overcrowding. With proper care, your astilbe will thrive and provide you with beautiful blooms year after year.
For gardens that are shaded, finding a perennial flower that offers more than just a few small flowers for color can be a challenge. However, astilbe (Astilbe spp. [Saxifragaceae]) solves this problem by providing both showy and vibrant flowers that brighten up shady spots, as well as impressive height.
The feathery plumes of astilbe flowers, which come in shades of pink, red, purple, or white depending on the specific type of plant, sway gracefully in the wind. One species, Astilbe biternata, is a native North American astilbe and is known for its white flowers and tall height of 6 feet, which is taller than other species and cultivars.
Astilbes also vary in their bloom time, with some flowering from spring to summer and others blooming later in the year. Many enduring astilbe plants available in nurseries are hybrids bred by George Arends, which can be identified by his name in the scientific name.
Astilbe is an excellent choice for shaded sites where sun-loving plants struggle. It thrives in woodland gardens, shady borders, cottage gardens, and even in containers on sheltered decks and patios. Taller astilbe plants make a striking statement as standalone specimens in large containers, while shorter types can be used individually or as part of a mixed container planting.
To enhance the beauty of astilbe flowers, pair them with other shade-loving plants known for their foliage, such as hosta, coral bells, and Solomon’s seal.
Plant Profile: Astilbe
Astilbe Planting Guide
- Common Name: Astilbe, false goat’s beard, false spirea
- Botanical Name: Astilbe spp. (Saxifragaceae)
- When to Plant: Spring or fall; avoid planting during the heat of summer
- USDA Zones: 4-9
- Sun Exposure: Shade, partial shade, dappled sunlight
- Soil Type: Moist soil that’s rich in organic matter with a slightly acidic pH of 6.0
- Signs of a Problem: On dry soil, foliage will curl and turn brown
- Signs of a Healthy Plant: On moist, fertile soil in a shady location, the foliage is green and healthy
Starting Astilbe From Roots
Since most astilbe plants available in nurseries today are hybrids, any seeds they produce will not have the same characteristics as the parent plants. Astilbe is typically sold as bare-root plants, as it is a clumping perennial that multiplies from its roots.
Plant astilbe roots in the spring, just before or after they come out of dormancy. The roots may already have small sprouts, buds, or eyes from which stems will grow. Alternatively, you can dig up your own astilbe plants in the fall, divide the roots, and plant the divisions. Spread out the roots in a hole that is twice as wide as their spread and plant them with the eyes barely visible above the soil.
If the soil is dry or poor, improve it by adding organic matter like well-aged manure or compost. After planting the roots, fertilize with an organic 5-5-5 fertilizer. Water thoroughly to ensure the fertilizer reaches the roots and keep the soil consistently moist.
Best Growing Zones for Astilbe
Astilbe is a perennial that thrives in USDA zones 4 through 9. It prefers to be protected from direct sunlight in most of these zones, especially in warmer climates. In the coldest parts of its range, astilbe can tolerate more sun, but in the warmest areas, it requires protection from afternoon sun. In the South, where summers are hot, astilbe also benefits from partial shade or dappled sunlight, even in the morning.
Failing to find a suitable shaded spot for growth can cause astilbe plants to suffer from excessive sun exposure, resulting in poor flowering performance.
When is the Best Time to Plant Astilbe?
Plant astilbe as soon as the ground is workable in spring, typically from mid-April to early May. By planting well before the summer heat arrives, you give the roots enough time to establish and support the growth above ground. A well-developed root system also enables the plant to absorb water and nutrients, promoting healthy growth and abundant flowering.
Alternatively, you can plant the roots in the fall if your garden falls within astilbe’s winter-hardy range. This allows the root system to develop throughout the winter. If planting in the fall, apply a layer of mulch to insulate the roots.
Tips for Soil, Sunlight, and Water
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Astilbe thrives in shady areas, often found under the shade of trees, particularly in woodland gardens. However, planting under trees can be challenging due to the difficult soil conditions caused by tree roots. Additionally, astilbe must compete with tree roots for water and nutrients.
While raised beds may seem like a solution to this challenge, it is not recommended. Piling soil on top of tree roots, as done in raised beds, suffocates the roots and prevents oxygen from reaching them, hindering the tree’s growth.
A better option is to prepare an in-ground bed by improving the soil around the tree. Spread several inches of organic matter around the tree and incorporate it into the existing soil. It is best to manually dig the soil instead of using mechanical cultivation, which can damage the tree’s root system.
Astilbe can grow in full shade, but it generally thrives and produces more flowers with some daily sunlight. A little morning sun is acceptable, but full sun all day or for most of the day is too much. Another ideal location is under trees that filter sunlight throughout the day with their leaves.
Astilbe plants perform best in evenly moist soil. This doesn’t mean the soil should be wet or soggy, but rather that it should not completely dry out around the roots. Applying organic mulch, such as finely shredded pine bark, serves two purposes: keeping the soil moist and maintaining its fertility as the mulch decomposes.
When fertilizing astilbe, use a light hand. During planting and in early spring of the following years, add 1 to 2 inches of well-aged compost around the plants. Follow the directions on the label to apply an organic 5-5-5 fertilizer. Make a second application of the same fertilizer in early summer.
Propagation of Astilbe
As astilbe plants grow, their root systems multiply, forming large clumps. It is easy to divide these clumps and propagate new plants to transplant elsewhere in your garden. If you have placed astilbe plants in a location where they can grow freely, such as a woodland garden or along a pond’s edge, there is no need to divide them unless they become overcrowded and flowering declines. However, you may choose to divide your astilbe plants if they exceed the boundaries of your chosen garden spot.
Divide astilbe clumps every three to four years or when they have outgrown their space. If dividing in early spring, dig the plants when new growth starts to emerge. If dividing in late fall, wait until after the plants have finished flowering and cut off the foliage before digging.
Water your astilbe plants thoroughly the day before dividing them and prepare the new location’s soil for transplanting. Gently lift the clumps using a shovel or long-handled garden fork, and cut them into 12-inch-diameter sections with a garden knife or shears. Before each cut, sanitize your cutting tool by wiping it with or dipping it into a 70 percent isopropyl alcohol or ethanol solution.
Immediately after dividing the sections, plant them and give them a good watering. Keep the soil moist to help the transplanted roots adjust to their new location.
Steps to Prepare Astilbe for Winter
While you have the option to remove the flower plumes earlier in the season after they have finished blooming, many gardeners choose to leave them as they still retain their color even when dry. Before the plants go dormant in the winter, clean up the garden area by cutting the foliage and spent flower heads to the ground. It is best to remove the cut foliage from the ground to prevent pests and disease pathogens from harboring over the winter.
Common Issues with Astilbe
Astilbe plants are not commonly affected by insects, diseases, or pests such as deer and rabbits, which can be problematic for other plants in the garden. Most problems arise due to cultural or environmental factors, such as excessive sun exposure and dry soil, which can lead to foliage burn and even plant death in severe cases.
Typical Diseases Affecting Astilbe
Astilbe may occasionally be affected by two fungal pathogens. Leaf spot, caused by the Cercospora pathogen, and powdery mildew, primarily caused by the Erysiphe polygoni pathogen, can impact the foliage of astilbe plants. Leaf spot appears as small brown spots that may grow and merge, forming larger necrotic areas. Powdery mildew appears as a white powdery substance on the upper surfaces of the leaves.
Using a fungicide after observing these symptoms rarely solves the problem, as fungicides are more effective when used as a preventive measure rather than a curative solution. If your astilbe plants are affected by either of these diseases, apply a preventive fungicide early in the following season to young plants, following all label recommendations regarding the application rate, timing, and frequency.
