April is the month here in the Northeast when we should get our tubers out of storage and begin to get ready for the new season. If we packed our tubers away as clumps or part clumps it may be quite difficult to spot the eyes and therefore not an easy task to divide them.
We should first bench the clumps up as seen in the picture. Using a good grade of potting soil and a plastic tray and some heat we should begin to see growing eyes in a week or two. The potting soil should be damp but not wet, place the clump so as the crown part is not in the soil. Just have the end of the tuber in the soil. At this point light is not that important. As soon as some eyes start to push up we then need to get some light.
Once we have some well defined eyes and they start to grow we can begin to divide. Using a sharp knife we carefully separate the tuber with the crown part and growing eye from the clump. Be sure to mark the tuber with its name as all tubers look alike at this time. Place this tuber in a new tray with potting soil or in a large pot so it may start to grow. Be sure there is a good light or the plants (for they are truly plants now) will tend to get leggy. After removing all tubers with growing or visible eyes return the rest of the clump to the soil and check in a week for additional eyes.
There will be times when it is just impossible to get at some of the growing eyes. They may be underneath the tuber clump or be so entwined that to try and cut the tuber out will result in the loss of the growing part. In these extreme cases use you good judgement as to whether to proceed or just let it grow and remove as much material as possible. There will be times when we have 2 or more eyes growing from one tuber. The proper practice is to remove all but one growing eye and discard the others. There is a way to save these growing eyes and increase our stock. The following procedure has worked for me many times.
Allow the shoots to grow to "cutting" size (about 3") the carefully with a sharp knife cut off a part of the crown with the shoot and place it at once in a small pot with moist potting soil. Most times this "crown cutting" will root in a week or two and we have an additional plant. This procedure works well before we plant the tuber in the garden. Do not try this procedure when the tuber has been planted out as it should not be disturbed once in the garden. These extra shoots must be removed and discarded.
If you have divided your clumps in the fall when the eyes are showing there is no need to be concerned with the above. Just place your tubers tail first in some moist potting soil and wait for those eyes to start.