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Following on from my guide on how to take delphinium cuttings and how to grow and care for delphiniums, the best time to divide a delphinium is in early spring. Dividing the plant lets you plant each new section separately and so provides you with more plants and blooms plus the original plant gets a chance to put on a show again as they can become tired and less productive if just left as they become congested.
Prepare the holes into which the new sections of delphinium are to be planted.
Lift the delphinium, root and all, from the ground in early spring on a cool, dry day. Do this by digging around the plant, about 20cm away from the stem. This helps you not damage any of the roots as you lift out the root ball. Dig around at an angle to get under the root until you can lift the entire plant from the ground.
Wash the root ball using a watering can and fine rose to get rid of any dirt and debris. Now you can check to see if there’s any root rot or other disease. Use a sharp knife and downward cuts, slice off the infected parts.
Tease out the roots and gently pull apart the plant. Delphiniums have quite fleshy roots so you may need to cut the pieces off. (Remember to sanitise your knife if you cut off diseased parts first.) Take off clumps with three to five healthy shoots. These newer sections should be about 20% of the original plant and root size.
Place the divisions in their new holes in the ground. Make sure that the tops of the roots are level with the ground. Fill in the rest of the hole with good compost and water the plants in thoroughly.
Divide a delphinium about once every three years to ensure its continued health and growth, and long life.
An alternative and sometimes I have found it to be a better way to propagate my delphiniums is to take basal cuttings. I explain all about how I do this in my article How to grow delphiniums from cuttings.