For the past few months I have been trying to grow a peppermint plant indoors. It grows pretty well except for a few stems that have gone purple and only seem to be able to grow these small leaves and seem to be trying to dig their way into the substrate. Should I be concerned about it? What is the cause of these stems?
Its making a bid for freedom! Mint produces long shoots below ground which have the habit of popping up a couple of feet away - when it can't do this,it will try to find another way round it. Mint will rapidly outgrow a container at root level; in the ground, it will send roots down deeper than its able to contained in a pot, so if you want to keep it growing healthily, it's necessary to turn it out, split it, discarding inactive areas at the centre if there are any, and repot into separate containers using fresh potting soil. This will be necessary once a year, possibly more often.