No matter what variety of potato you’re growing, the chances are, at some point, you’re going to need to mound up your potatoes. What that means is that you cover the shoots that are poking through the ground with soil. People call this process different things – so you may hear people refer to this as “earthing up”, “covering over” or simply “burying”, but they all mean exactly the same thing.
Mounding up the potato plant helps to encourage as much growth of potatoes along the stem of the plant while also protecting the potatoes from being exposed to light. Nobody wants green potatoes! If your potatoes are exposed to sunlight, the bulb will start to produce a chemical called solanine and become inedible. When potatoes are left out in the sun too long they also produce chlorophyll, as a way to turn the energy from the sun into food.
This year, I’ve started earthing up my potatoes a little bit earlier because of the unpredictable weather, one minute we’re getting frost, hail, sleet and in the next we’re basking in glorious sunshine. The tops of the plant are around 12″-15″ tall, and this is about the time that you want to start earthing potatoes. I try not to cover the entire plant, and leaving some of the foliage exposed to the sun so that they can photosynthesize. Depending on how productive they are, I’ll look to repeat this every couple of weeks. In the past, my potato mounds have crept up to about one and a half feet high.
As I’ve mentioned before, mounding up or covering the potatoes also helps to protect to the shoots from the harshness of the frost. You can tell if your potatoes have been the subject to the cold conditions because the tops of the plant will look brownish and crinkly – if you see that, earth them up fast! I’ve seen people at the allotment over the tops with grass cuttings, newspaper clippings and even plastic – whatever you decide to use, make sure that you don’t compromise the plants access to water.