When And How To Divide Your Astilbes To Promote More Vigorous Blooms

Astilbes are a staple in the shade garden. With their delicate fern-like foliage and spikes of fluffy colorful flowers, they add color and texture to dark shady spots and beautiful accents to woodland gardens. These popular perennials come in a large variety of cultivars in a range of colors including white, pink, red, and purple. They grow over time into large clumps and need dividing every few years. Dividing them at the right time will help promote vigorous blooms, and the ideal time is fall, but early spring will also work.

Dividing your astilbes keeps them at a manageable size and keeps the foliage looking neat. Regular division of the plants also helps prevent any mildew or fungal problems that might occur due to lack of air circulation or excess moisture. This is especially important for shade plants as they may not benefit from the sun drying them out during damp weather. Astilbes do like moist soil but are susceptible to mildew if the clumping flower spikes become overcrowded, which can happen once the clumps get too big. 

When dividing your astilbes, look for signs that they are otherwise doing well in their chosen location. If the leaves show signs of being scorched, it means they're getting too much sun. It would be best to move the entire clump to one or more shadier locations. It's easiest to grow and care for astilbes when they're planted in moist, well-drained, fertile soil.

The best time to divide astilbes

Although dividing your astilbes in the fall is recommended, you can also perform this task in the early spring. In fall, you need only wait until the plant has stopped flowering, which usually happens late summer. You will also want to divide them before the nights get too cold to protect your plants from any possibility of a hard frost, which might damage a plant that is already somewhat stressed from being divided. But these cold hardy perennials are resilient enough to survive as long as you divide them before mid-October.

You can also divide astilbes in spring, but it's best to do it early. Astilbes tend to start producing new spring growth in mid to late April, so dividing them in early to mid April is good timing. This will get them established in their new spot before they start forming new flower spikes with buds. You can also clean up the divisions by removing dead or damaged plant parts, so they'll be ready to put their energy into producing new growth.

Just like you watch the frost forecast in autumn, make sure you're past the last frost date in your area before trying to divide astilbes in the spring. Even cold-hardy perennials can be left vulnerable when they are dug up and divided, and frost can stress out the plant, causing damage. Excess heat can cause the same stress, so dividing plants in the heat of summer is also not recommended.

Dividing and replanting astilbes

Dividing astilbes is pretty straightforward. The best way to divide it efficiently is to dig up the entire plant and divide it into sections, then replant the sections. You can dig up part of the plant but this might result in damaging the roots. By digging up the entire plant you can more easily separate the clump into sections which are visible from the root growth sticking up. 

Before digging it up, water it lightly to soften up the root system a bit. Then dig around the entire plant to loosen it before lifting it out. Divide the plant using a shovel or garden knife. Each new section should be at least six inches wide on each side so it produces some flowers; closer to twelve inches is better if you're dividing a large plant. The prepared hole should have enough room to tuck the new section in and add some fresh soil on all sides. 

Astilbes do best in rich, well-draining soil. So when planting, in addition to soil, add some compost, leftover coffee grounds, or peat moss to the hole to give the division some extra nutrients and improve drainage. Pat some soil over the top and water it lightly. Keep your transplants consistently moist for at least a week to help the divided astilbe get established in its new location.