How to Grow Astilbe in a Container
Grow a container of astilbe (Astilbe spp.), also called false spirea, for a splash of color in a shade garden or on a shady or partly sunny porch or patio. These plants grow anywhere from 6 to 36 inches tall and 12 to 24 inches wide, so you can find the right fit whether you want a compact variety for a small pot or a sprawling cultivar in a large planter. Astilbe grow in U.S. Department of Agriculture plant hardiness zones 4 through 9, with some variation depending species or cultivar.
A container of astilbe outdoors is less insulated from winter frost than astilbe growing in the ground. To make sure you don't lose this hardy perennial, select varieties two hardiness zones warmer than your area for your pot. For example, an astilbe labeled as hardy in USDA zones 4 and warmer will likely overwinter successfully outdoors in USDA zones 6 and warmer.
Varieties for Containers
You can grow tall varieties for height in patio planters or pick one of the dwarf types for a more compact look.
Compact Cultivars to Grow in Pots
- Chinese astilbe 'Pumila' (Astilbe chinensis 'Pumila') grows just 7 to 9 inches tall in part shade to full sun. This cultivar has pink flowers and grows in USDA zones 4 through 8.
- Chinese astilbe 'Finale' (Astilbe chinensis 'Finale') is another pink-blooming, 8- to 12-inch-tall cultivar hardy in USDA zones 4 through 9. This astilbe prefers part shade to full sun.
- Dwarf astilbe 'Sprite' (Astilbe simplicifolia 'Sprite') is also a pink-flowering astilbe ideal for even colder climates. It grows 10 to 12 inches tall in USDA zones 3 to 8.
Full-Size Varieties for Containers
- The 'Red Sentinel' cultivar (Astilbe japonica 'Red Sentinel') is a striking, bright-red astilbe that grows 24 inches tall in full shade to full sun. It is hardy in USDA zones 4 through 9. This sprawling cultivar grows 18 to 24 inches wide, making it ideal for large patio planters and half-barrel planters.
- The hybrid cultivar 'Bridal Veil' (Astilbe x arendsii 'Bridal Veil (Brautschler)') is a sprawling white-flowering cultivar that grows 24 to 30 inches tall and wide. It grows in part shade to full sun and is hardy in USDA zones 3 through 8.
Find the Right Container
Three things to consider when picking out a pot for astilbe are size, drainage and material:
- Look for a planter 16 inches or more around and at least 12 inches deep. Bigger planters, like half barrels and large patio planters, allow you to plant even more astilbe together.
- Every container you use must have a drainage hole, and ideally more than one, to allow excess water to escape. Pots without holes in the bottom collect water, drowning the roots over time.
- Container material matters. Terra cotta and wood planters allow more air circulation than less porous materials. This helps prevent soggy soil and root rot problems. Metal containers are aesthetically pleasing, but in summer, the excess heat trapped in the metal can overheat the plant roots. Glazed ceramic and plastic work well without getting overly hot but can trap water. If you intend to move the container around, a lighter wood or plastic pot is best.
Potting Soil Solutions
Use a standard quality potting soil to fill the containers and skip the garden soil. If you want to make your own potting soil, try one of these recipes to make a light, porous, well-draining potting mix:
- Equal parts peat moss, sand, perlite, compost and composted bark chips.
- One part sand, one part perlite and two parts peat moss.
- Equal parts pine bark, peat moss and sand.
Coconut coir, made from coconut husks, is a sustainable alternative to peat moss that you can use in your potting mix. Substitute coir for peat moss, keeping the volume the same.
Light, Water and Fertilizer
Astilbe grow in full shade to sun, depending on the type. Full shade means no direct sunlight, whereas full sun is a spot that gets six hours or more of sun per day. If you're growing a grouping of astilbe together in a large planter, space small varieties 6 inches apart. For larger astilbe, set them 8 to 12 inches apart.
Water when the potting soil dries out 1 inch deep. In general plan to water twice a week, but you may have to water more often in hot weather to keep the soil from drying out and less often in wet weather so that the pots don't get overly saturated. At each session, apply the water slowly until you see it start to leak out the hole in the bottom of the pot.
Fertilize twice a month beginning in the spring when the first new shoots appear. Stop fertilizing through the winter when astilbe go dormant. Use a liquid or water-soluble fertilizer. For each container, use 1 teaspoon of fertilizer mixed with 1 gallon of water.