Ask the Expert
It sounds as if they have one of the bacterial soft rots. If it were blight, it would smell bad, and the decay would start from the outside. You didn't say whether they were stored potatoes, or ones that you have just dug up. Either way, be sure not to plant potatoes on the same spot for another few years, in case the pathogens remain in the soil. Throw out all the affected potatoes (not on the compost heap), and keep a close eye on the unblemished ones. When storing potatoes, make sure that they are properly dried first.
Planting in August
Peat moss on its own is used as a soil conditioner rather than as a potting medium, as it doesn’t contain enough nutrients for most plants. House & Pot Plant Compost, which uses peat moss as a base and which contains other nutritious elements, is ideal for your croton.