On this page I have outlined how to grow potatoes in containers. The advice is the same whether you chose to grow potatoes in pots, or grow potatoes in bags, as I’m only going to look at the growing and maintenance bit here. The illustrations on this page has been borrowed from Unwins.
Start out by putting 6-8 inches (15cm-20cm) of good quality potting compost in your container. Alternatively you can use a multipurpose compost, mixed 50/50 with sharp sand and/or some well rotted farmyard manure or homemade compost. Adding the organic material to the mix will make watering easier throughout the season, and add valuable plant food which will boost your crop. You can also mix in chicken manure pellets with your compost, but be careful not to over do things.
Place 1, 3 or 5 chitted seed potatoes on top of the compost, depending on the surface area of your containers. As a rule of thumb use 1 tuber for a 10 inch (25cm) wide container, 3 tubers in an 18 inch (40cm) container or 5 tubers for a dustbin sized container.
Now, cover the tubers with another 4-6 inches (10-15 cm) of your compost mix on top of the tubers. After a couple of weeks you should see potato plants starting to sprout through, if it is warm enough. As this happens, keep covering them in more compost, until the level of compost reaches 2 inches below the top of your container.
This emulates the act of ‘earthing up’ soil grown potatoes, and will protect your tubers from light, and the potato plants from frost. Both essential for the success of your crop.
During this period of time you need to keep your potatoes well watered. You can apply a liquid plant food to the water as you go along, but only if you haven’t already added plant food to the compost. Over-feeding can have fatal consequences for your crop.
It is important to take care with watering, when growing potatoes in containers, because soil in containers dries out a lot quicker than on the ground, but at the same time you could end up over watering the crop.
In the height of summer you may well have to water twice a day, once in the morning and once in the evening.
Try to water straight into the soil, as the water will just run off the top of the plant, and spill onto the floor.
The time to harvest your potatoes varies according to variety. For first earlies and second earlies you can start harvesting when the plants stop flowering. Take the top off the plant, remove the compost, and take out as many potatoes as you need. The rest you can leave in the soil for up to 4 weeks.
If you have grown maincrop potatoes, the time to harvest them is when the tops of the plants drops and withers away. This will usually happen in the later half of September. Take the potatoes out of the soil, and leave them to dry, before storing them away for winter.