When is the best time to divide Hostas?
The best time to divide Hostas is in the the early spring as soon as they start to break ground. The sooner the better.
More answers to hosta questions: How to Plant, Grow, and Care for Hosta – Plantain Lily
When to divide and transplant Hostas?
Hosta may be divided or moved at anytime. However, given the increased shock to the plant caused by dividing or digging it up to be moved, spring has been much preferred. In fact, it is recommended that dividing occur before the plant begins any substantial spring growth.
There is another school of thought and that is, if you follow the life cycle of a monocot the best time may be the Fall. Under this school of thought, in the spring, if you divide you will need to give the plant more food as it needs food for foliar development as you have damaged the crown where food has been stored to aid in the foliar growth, you can divide in the summer but, since you are damaging roots, etc., you will need to add substantial amounts of water to compensate.
Finally by dividing in the fall the plant has gone predominantly dormant but is still in the root development phase and dividing at this time does the least harm!
Please also look into Preparing Hostas for Winter – “winterizing” Hosta.
How to split Hostas
Once the eyes are evident, the plant should be dug and divided by using a sharp knife. It is also recommended that the knife be dipped in a fungicide before making the cut, and that the cut surface be dusted after the cut is made.
Transplanting Hostas: how do you plant a Hosta?
You should plant the hosta in an area that is shady and protected from the afternoon sun. Mix the soil with some compost and make sure that the soil mixture is loose. You can also add some slow release fertilizer. Make sure that the root clump is level to the ground and water it well.
For more info on dividing plants, please see Dividing Outdoor Plants for Propagation.