I would like to plant a second crop of potatoes in July. Could I use
potatoes dug from my first crop this year or should I try to find seed
potatoes?
You can plant mid-season and late potatoes this month, but there are
particular varieties that are best suited to planting at this time. This
is one reason not to plant the potatoes you just dug (which are
an earlier variety).
Here are links to additional information:
From the University of Illinois Extension.
Growing Potatoes in the Home Garden from UC Santa Cruz.
Steve Solomon’s Growing Vegetables West of the Cascades (Sasquatch Books,
2000) says that because of the large number of viruses which can affect
potatoes, you should not carry over your seed (replant). It is safest to
use certified virus-free planting seed. He says that your crop might be
fine the first time you replant your own potatoes, but they will become
increasingly susceptible to viruses.