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If you are going to divide an existing parent plant, you can do it very easily at multiple points throughout the year and you have the option of taking your divisions and transplanting them immediately, or hanging on to them and transplanting them later.
When to divide astilbes
You can successfully divide either in the Autumn or the beginning of Spring as you do with most perennials with latter probably being the prefered time as they are starting to root as they come back to life after being dormant over winter.
Dividing astilbes Spring
If you are planning to divide in the springtime, you want to do it in the early spring. You should do this when the plants are still in their dormancy. The reason for this is that you want to give each of your divisions adequate time to get established throughout the season.
Dividing astilbes in Autumn
If you are planning to divide in autumn, each of the divisions you take from the parent plant should be stored in potting compost in containers, somewhere dark and cool like your garage over winter which is why we prefer to do it in spring is possible. They can then be planted in their permanent location in the early spring. It is always best to wait and divide the rhizomes after your parent plant has finished flowering.
How to divide and split established astilbes
If you are dividing and planting immediately, make sure you have an area in mind ready before you start the division process so that your divided plants can be transplanted immediately. If your dividing in Autumn all you need is some empty pots and some compost to keep them in over winter
- The first step is to water the area around your astilbe you’re going to divide. You want to water it thoroughly and let the water settle so that the soil is much looser. This will make it easier when you have to remove the plant for the division.
- As mentioned, make sure that you have the new position if you’re going to transplant your divisions immediately, and dig the holes ahead of time. These holes should be around 20cm deep and between 30 and 45cm apart. If you are going to improve your soil by adding compost, dig the hole a little deeper so that you have room to mix it in.
- Take the parent plant and remove any debris from around it or plant material on top of it by cutting it away with astilbes so your just left with the root system at ground level. Then measure a diameter approximately 20-30cm, around the plant, from the base and mark it somehow. This is where you’re going to start the digging when you divide your plant.
- Using a spade, dig the plant out keeping around the diameter mark and digging out in the shape of a large bowl. The idea is to keep a lot of soil intact so you don’t damage any of the roots when you remove the main plant from the ground. The less damage you can do to the parent plant, the more divisions you will have and the faster the parent plant will recover.
- Hold the astilbe root system and look for the “eyes” on the rhizomes. The eyes are where small shoots come out of the rhizome. Pinch off sections of the roots with 3-5 eyes. A single established astilbe should give you an average of four or five divisions.
- Place your fresh transplants into their holes with the eyes facing upward, or place them in a container for storage over winter if you are doing this in autumn. If you transplant them immediately make sure you water them thoroughly and if you transplant at the beginning of Spring, give the mixture some fertilizer such as bone meal or growmore to give them a boost.
If you take your divisions in Autumn and store the new plants, put them in a container with well-draining potting soil, we recommend using multipurpose compost with some grit mixed in and leave the container somewhere dark like your shed or your garage. Over the winter they don’t need a lot of water or any food. You also don’t want to leave them completely dry because the roots can dry up. Check how moist the soil is and maybe water the containers every 2 or 3 weeks and that should be enough to get them through until springtime.