Swift potatoes for the impatient gardener

You'll sometimes see "extra early" potatoes offered in seed catalogues.

Technically there's no such category - they're just particular cultivars of "first early" spuds which have been bred to take the least possible amount of time between planting and harvesting.

There are only two varieties commonly on sale, rocket and swift.

I've grown both many times and I can't say there's a huge difference between them. Swift is generally said to have a stronger flavour than rocket, and its individual tubers tend to be larger.

Rocket on the other hand probably has slightly higher yields. They both make compact plants, suitable for growing under cover, but swift even more so than rocket.

In truth, neither of these extra earlies would be likely to win prizes for flavour or for yield.

But then, that's not what they're for. Really the only point of extra earlies is that they are extra early.

If you can plant them in January or early February you should certainly be able to start eating them before the end of April. In a good year, they can be ready in just seven weeks.

To start potatoes off so early, you need two things - protection against frost, and to get hold of the seed tubers around Christmastime.

The latter is out of your hands. The seed companies will send out the tubers for planting from December, when the weather permits.

As soon as they arrive, unpack the potatoes and set them to chit - that is, to grow short, sturdy green shoots, so that they'll start into growth rapidly when eventually planted.

Set the tubers upright in egg boxes or trays in a frost-free, light place.

The windowsill of an unheated spare bedroom is ideal, but gentle heat won't do any harm. The potatoes are ready to plant when the shoots are half an inch to an inch long.

Because the aim is early cropping I think it's only worth growing extra earlies under cover. Ideally, put them in an unheated greenhouse, but plastic tunnels and cloches will also serve.

If you are using a greenhouse, by the way, note that the glass will probably be grubby from the winter storms, so give it a wash first to let in as much light as possible.

I plant my extra earlies in tubs, in a peat-free multi-purpose compost.

A pot about 14" across by 12" deep is perfect.

Over the years, I've become convinced that all potatoes give highest yields when there's only one tuber in each container, rather than the conventional advice which is to plant three or four in a larger tub.

Start with three or four inches of compost in the pot, nestle the tuber in that and then fill the pot up with more compost. Keep the pot well-watered - it must never dry out.

The easiest way to tell when to harvest is to gently poke your fingers into the compost and feel the size of the spuds.

• Follow Mat's gardening tips on Twitter @StarGardening.