Potato barrels are usually a very poor way of growing potatoes. The story goes like this - you start with a small amount of compost in the bottom of the barrel, and add your tubers. As the plants grow, you gradually fill up the barrel with compost. When they reach the top, and eventually die down, four months later, you will have a barrel full of potatoes.
Unfortunately it doesn't work like this. If you use a barrel, you will probably get a miniscule crop (a couple of pounds of tubers at most) and a rather stagnant smell as you empty out the compost.
A potato barrel will probably set you back £25. What you get is a flimsy container worth less than a fiver, quite incapable of doing what it's supposed to do.
WHY THEY DON'T WORK
Potatoes need air, not just water and light. The potato barrel concept doesn't work because the compost can't breathe. Once the compost is wet it can't dry out, and the tubers will either grow very slowly or start to stagnate.
Much better value are 3-gallon builders' buckets. These can be obtained for £1 each from "pound shops" and elsewhere. Drill about thirty one-quarter-inch holes in the bottom with a powerdrill for drainage (place the bucket right-way-up on a board before drilling, and drill through the bottom of the bucket). 2-gallon florists' buckets are also good.
A 3-gallon bucket can grow about three or four tubers depending on variety. Add a little compost at the start, placing the potatoes at the bottom. As they grow, add compost until the bucket is full. Then make sure the plants receive plenty of water and light.
You can expect a crop of between 2 and 4lb tubers per bucket from reasonably vigorous tubers such as Maris Piper, with an average of about 3lb.
I've become aware of a very interesting set of notes on 'how to grow potatoes' at www.igardenplanting.com - I recommend you take a look. There are also interesting sections on cooking potatoes in different ways.
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