Although spring and fall are the best times to divide perennials like hostas, you can divide them successfully in the summer. Here are the most important steps to follow to ensure a healthy summer division.
1. Cut Back the Leaves
Cut back the hosta leaves to within a few inches above the ground before you dig the plant up. Not only does this enable you to see where to dig more easily so as not to damage the roots, but less leaf growth means more energy going to the hosta division's roots after transplant.
2. Divide the Hosta
After lifting the hosta from the ground, divide into as many parts as you choose. Any division that has a good, healthy root system attached will be fine.
3. Soak the Division Roots
Soak the roots of the division in water for half an hour or so for the roots to soak up as much water as they can before replanting.
5. Plant the divisions
Plant your divisions in well-draining soil in a hole twice the width of the roots. Tuck the roots in pointed downward and the eyes or growing points slightly below the soil surface.
The best soil for hostas is one that is rich in plant foods (compost), retains moisture well yet drains easily.
Hosta roots can grow anywhere from 6 to 18" deep depending on the size and variety and require plenty of space between plants for good air circulation.
General spacing for different hosta sizes is as follows:
Very Large to Large Hostas 30 - 36"
Medium Hostas 18 - 24"
Small Hostas 12 - 18"
Mini or Dwarf 6 - 8"
6. Water in well.
Water the divisions every day and even up to twice a day in the hottest weather. Hosta roots need at least 1" of moisture per week for healthy growth, and hosta divisions need even more water than that for the rest of the summer, and even into the fall.
Why water into the fall? It's helpful to remember that when a hosta emerges in the spring, it is emerging on the energy and food reserves that the plant stored in its rhizome late the previous summer and fall. If the hosta received sufficient water in late summer and fall, it should emerge the next spring as a larger plant because it was able to store away more energy than it used.
However, a hosta that does not receive adequate moisture in late summer and fall cannot build up the energy reserves it needs to increase in size. The result is a hosta that grows to the same or smaller size the following spring.
Cover the soil with a 2-inch mulch layer to help conserve moisture.
Fold a piece of cardboard in half and tent it around the divisions for up to a week. As soon as the hosta appears to bounce back with some leaf growth, you can take the cardboard off.
- No Need to Fertilize --
It is recommended to stop fertilizing hostas two months before your expected first frost date. This allows the hostas to slowly settle into their winter dormancy. So if you have divided in mid to late summer, no fertilizer is needed.