From our perspective, the best time for this significant change is during our dormant or slow-growth periods. For most Delphinium varieties, this is in early spring, just as our new, green shoots emerge from the crown and are only a few inches tall. The soil is workable, and the cool, moist conditions allow us to recover from the shock of division without the added stress of intense heat. Alternatively, you can perform this task in early autumn, after our flowering show is over but while we still have at least six weeks of mild weather to re-establish our root systems before the ground freezes. Dividing us at these times gives us the entire growing season to focus on root development.
Begin by hydrating us thoroughly a day before the operation; well-hydrated tissues are more resilient. Gently dig a wide circle around our base, taking care to lift our entire root ball from the earth with as little damage as possible. Shake or wash off the soil to clearly see our crown and root structure. You will notice that we grow from a central crown with multiple growing points, or "eyes." Using a sharp, clean knife or spade, cleanly slice through the crown to divide us into sections. Each new division must have at least two to three healthy shoots and a substantial portion of our fleshy, white roots attached. Smaller divisions may struggle to survive. Trim away any dead or rotten parts of the crown and roots—this is like pruning away weakness, allowing us to direct all our energy into vigorous new growth.
While we are out of the ground, prepare the new planting sites. We Delphiniums are heavy feeders and require deeply cultivated, fertile, and well-draining soil to thrive. Amend the planting holes with plenty of compost or well-rotted manure; this rich banquet of nutrients will welcome our roots and encourage them to spread. Ensure the location receives ample sunlight—at least six to eight hours daily—and has some protection from strong winds, which can easily damage our tall flower spikes.
Plant each of our divisions at the same depth we were growing at previously; the crown should be level with the soil surface. Planting too deep can cause the crown to rot, while planting too shallow exposes our sensitive roots. Firm the soil gently around our roots to eliminate air pockets. Then, water us in deeply and thoroughly. This "settling in" water is crucial for making good contact between our roots and the soil, providing the moisture we need to begin our recovery. Apply a layer of mulch around our base to help conserve moisture and keep our root run cool, but be sure to keep the mulch a few inches away from the new shoots to prevent rot.
Our immediate need after division is consistent moisture. Keep the soil evenly moist, but not waterlogged, for the first several weeks as we work to establish ourselves. We will be directing our energy downward, building a strong new root system, so you may not see dramatic top growth immediately. Please be patient with us. With the right care—ample water, rich soil, and plenty of sunshine—we will reward your efforts with robust health and spectacular blooms in the coming season, having been rejuvenated by the process of division.
