I usually put mostly black gold compost in the bag so it should have enough nitrogen. This is actually how I inadvertently introduced the pests the first year. I used compost that wasn't ready. I made sure to not make that mistake in Year 2... However I usually don't add more compost or Potassium later in the cycle.... With 1 exception. Last year I did an experiment where I grew potatoes in a 4 ft basket made from chicken wire. Instead of using soil, I used dead leaves I raked up. In that case, I DID add compost intermittently. That seemed to work extraordinarily well except that ants or some other kind of pest got to the potatoes before I did...Did your soil have too much nitrogen or did you fertilize?
They are heavy nitrogen feeders for the first couple of months and then for the last 60 days before harvest, you need to go higher in a potassium feed.
