If you want a few freshly-dug spuds to go with your Xmas dinner, or a meal or two before anyone else has harvested their first earlies, growing potatoes in your polytunnel is the way to do it – in late August for an Xmas crop, or mid-February to dig in late April. Otherwise, if you’re growing for a storage crop, you’ll need quite a bit of room – so an outside bed is probably better.
Potatoes can suffer from frost, pests and blight. Even though some blight-resistant varieties are now available, resistance isn’t complete. There are no guarantees. Fortunately, despite blight and pests such as eelworm and keel slugs, it’s still possible to get a fine crop. You just have to be a little more careful, especially about the variety you plant.
To give your spuds a good start, ‘chit’ them. This means allowing them to sprout shoots for a week or two before planting them. Put them into egg boxes and place them on a windowsill in a frost-free room. Pretty soon they’ll begin to chit. If this happened in the dark, the shoots would be long and weak. In daylight, they’ll be strong and short – and all the time spent chitting is productive growing time while you’re waiting for the frosts to be over.
Potatoes are hungry crops that like a rich, water-retaining soil. Dig in plenty of manure, and be sure to rotate! Don’t plant potatoes where they’ve grown in the previous two years. Once the bed has been dug over, create trenches roughly 40-50cms apart with ridges 15cms tall between them. Set the chitted potatoes (with the best chits pointing up) roughly 10cms deep, every 25cms along the trenches
When the plants get to be 10-15cms tall, use a rake or hoe to carefully pull earth down from the trenches to cover them again. You’ll only be able to do this a couple of times before the trenches are all gone, but each time results in better, longer root growth – which in the case of potatoes means a higher yield.
A mulch between the rows conserves heat in the earth which again helps to produce a bigger crop. At the beginning of the season, a mulch will also help protect the plants from any late frosts. Potatoes are not at all hardy, and frost will kill the leaves – or the entire plant.
Flowers on the plants show that potatoes are beginning to develop below the surface. For early varieties (which are eaten young or ‘new’) that means they’re ready to lift, but maincrop potatoes need a few weeks more to bulk up. When you’re ready to harvest, start digging with a fork near the edge of the bed to avoid damaging any tubers. Those that are damaged can’t be stored except by freezing as mash. You can also dig down at the edge of the bed and ‘rootle’ (that’s a technical term) around, giving you the first new potatoes of the season.
The longer the plants are left in the ground, the higher the risk of blight or damage from pests. Blight, a wind-borne disease, spreads extremely fast and can also affect tomatoes. If you see any signs on the foliage (see below), cut down the affected ‘haulm’ – i.e. the part of the plant which is visible above the ground. This stops the disease travelling down the stem and into the tubers. If you plan on storing the crop, leave the soil undisturbed for at least two weeks after removing the haulm, or live blight spores on the earth may infect the tubers which could then rot in storage. Check stored spuds every couple of weeks and remove any that show signs of spoilage.
Eelworm and slugs can drill holes into your crop and ruin it for long-term storage. However, you can still cut away the affected part of the potato, mash the remainder, and freeze for future use.
Depending on your climate, you can choose first early, second early late (‘maincrop’) varieties. The earlier the crop is out of the ground, the less likely it is to be affected by blight, slugs or eelworm. However, many people would say that the later varieties have the best storage and taste!
Here are a few varieties to try:
Early – harvest in July
Produces long, oval tubers with an attractive red skin and yellow flesh. Some resistance to blight and other diseases.
This has the highest blight resistance of any ‘early’ potato, and some other diseases too. Additionally, it stores well and is also grown (commercially) as a second early, or even an early maincrop.
Second early – harvest in August
Good resistance to blight and scab. This variety can tolerate some drought, so it’s a good choice for sandy soils which drain quickly. It’s great as a baking potato, and also for chips.
Early maincrop – harvest in September
A favourite variety and very well known in the UK. It’s also tasty, and great for almost any use. Produces big potatoes that store well.
Possibly our best known spud, King Edward has been around since the early 1900s. It’s a ‘heritage’ variety, great for roasting, and a good all-purpose potato.
Late maincrop – harvest in October
A very good choice for long-term storage with good blight resistance. Great for roasting and baking.
Isle of Jura
Pale tubers with a yellow flesh and some blight, scab and eelworm resistance.