If you are making your own slips the only issues are:
- Sweets cannot get cold. Even leaning against a late winter window can frostbite them.
- Don't let the vines that grow touch the old potato or the water it lives in. Cut them cleanly and remove them to a new jar forever. If you have any diseases in your soil (or if you are using a store bought potato especially) you will bring them with the slips if you aren't careful.
- Slips are ready to plant when they have a few nice roots, although I bought mail order slips our first year and they were just vines freshly cut from the potato, with no roots at all. (And they did well. If interested, I bought them from Brown's Of Omaha. The sweets I am starting this year are the same plants, just saved from year to year!)
- One should never plant slips too soon, because their growth in the ground has very little to do with how long they have been in the garden, and everything to do with soil temperature. Here (zone 6b) we wait until the very end of May. They can be nursed along in a well-nourished liquid until it is time to plant.
We had such good luck last year with black plastic mulching over soaker hoses, making holes for just the slips. We just happened to have the plastic somehow and it worked out. I do not think we'll be utilizing that method this year, however, because we are planting sweets in our pig pen from '08. It has been left alone for all that time and is perfectly ready for a leave alone crop like sweet potatoes. We hope to fill it up and let it run wild. Also, I would not wish to buy plastic for that purpose.