Repeatedly, I come across advice to grow potatoes in a stack of car tyres. Old car tyres, when exposed to sun and rain, can leach heavy metals into soil. One of the heavy metals in car tyres is cadmium, which is known to cause cancer in humans and animals. Potatoes are very efficient at absorbing cadmium from soil, and it is not advisable to grow food crops, especially potatoes, in car tyres, or to use car tyres as compost containers.
However, if you are short of space, there are other containers suitable for growing potatoes.
Potatoes can be grown in double hessian bags, drums with plenty of drainage holes, stacked foam vegetable boxes, or wire hoops called potato cages. The newer, woven plastic feed bags may not be as efficient as the good old hessian bags, as they tend to break down quickly when exposed to sunlight. Most of these methods require one container per plant, but they allow for plenty of hilling-up and a hilled container plant will produce a larger crop than an un-hilled potato plant grown in a garden bed.
Always use a good quality potting mix for container plants, as the cheaper mixes tend to become water-repellent quite quickly, and garden soil tends to become compacted in containers. If soil is compacted, it is difficult for tubers to form. Potato plants are reasonably heavy feeders, so add a decent amount of complete organic fertiliser to the potting mix in the base of the container. Also, remember that potato plants take about 20 weeks to mature and growing mix in containers stays warmer than garden soil. Position the container where the mix won’t overheat in the warmer months.
Cultivation and hilling-up are as indicated in the “Growing potatoes” post here on Aussie Organic Gardening.
To grow potatoes in bags
Place one hessian bag inside another, and roll the sides of the bags down so that the seed potato has 15 cm of mix below and above it after sowing. As the plant grows, gradually unroll the sides as you add more potting mix.
To grow potatoes in small to medium drums
Seedlings will not receive as much light as those grown by other methods, as the seed potato is sown 20 cm from the base of the drum to allow plenty of room for hilling. Place drums in a well lit area. Ensure that the drum has plenty of drainage holes near the base. If the drum is deep, put several centimetres of gravel in the base of the drum before adding the potting mix.
To grow potatoes in foam boxes
This method requires two deep foam vegetable boxes of the same size for each plant. Make sure at least one box has plenty of drainage holes in the base. Place a sheet of wet newspaper in the base of a box with plenty of drainage holes, and cover the paper with 2 or 3 cm of gravel. Place 15 cm of potting mix in the box, sow the seed potato, and cover with another 15 cm of potting mix. Place a 60 cm stake in each corner of the box – these will hold the second box in position. Cut the bottom out of the second box. Hill the plant by placing the second box over the first, and adding more potting mix as the plant grows.
To grow potatoes in a wire cage
This method requires a 3-metre length of stiff wire mesh, about 1 metre wide. This will provide a hoop a little less than 1 metre in diameter. Wire used for concreting has holes large enough for harvesting chats through the mesh. Construct the hoop and mark the diameter on the ground. Sow 4 seed potatoes in the ground, evenly spaced within the circle, keeping them well inside the perimeter. As the plants grow, they have straw packed around them, or straw and compost, if it is available. Make sure the potatoes are well covered, or they will become green.