A perennial should be divided if its center is dead or very sparse (resembling a doughnut), if it has decreased in size over previous seasons, if it stops producing or produces fewer flowers than usual, and if it is becoming overcrowded by or is overcrowding other plants.
Spring is generally the best time to divide perennials. It is best to divide peonies in the fall, bleeding hearts and oriental poppies in early fall, and bearded irises only after they have finished blooming.
- Transplant fertilizer (10-52-10 formula) or bone meal
- Sharp spade or knife
- Garden fork
- Pruning shears/secateurs
- Pots or bags
- Prepare the soil for the areas to be planted. For instructions on soil preparation, please see “How to Prepare an Area for Planting.”
- Loosen the soil around the outside and underneath the plant you will be dividing. Using a pot or bag, lift the plant with as much soil as possible.
- Split the plant apart, ensuring that each section has plenty of roots. If the plant’s centre has died, cut around the center and discard it.
- Use a spade to split large perennials and ensure that each portion has at least 3 stems.
- Use a knife to split smaller ones and ensure that each portion has at least one growing point.
- Some plants can be pulled apart with your hands. Ensure each piece has a stem.
- Replant the newly divided plants. Cover the plants with soil no deeper than they were before they were divided.
- Water with transplant fertilizer (10-52-10 formula) or add bone meal to the soil to encourage rapid root development. Do not fertilize after August 1 to allow the plants to prepare for winter dormancy.