Potatoes grow best in open ground in full sun. If grown in the shade you will still get a crop, but the growth above ground will be long and spindly as it reaches for the light, and you will get a smaller crop as the energy will be diverted into leaf production rather than the roots. it is also wise to follow a crop rotation plan, and try to avoid growing potatoes on the same ground on consecutive years.
Preparing the Ground
Potatoes grow well in most soils, but for the best results dig the ground in Autumn/Winter and manure as you dig - horse manure, your own compost, or even green 'council' compost can all be used.
Preparing Seed Potatoes for Planting
The act of chitting potatoes is a much debated topic amongst vegetable gardeners. Some chit their potatoes religiously, and others don't bother at all, and just plant the seed potatoes as they are. In theory chitted potatoes have a longer growing season, and therefore produce a heavier crop of potatoes. In my opinion it is well worth chitting your seed potatoes, and besides it's so easy to do, then why not. If however you are behind with your planting and have not had time to 'chit' then don't worry too much - just plant them anyway, however you will get a smaller crop.
To chit your seed potatoes place them in egg boxes with the end with most eyes pointing upwards. Keep them in a light place (but away from direct sunlight) at about 18°C until they start to shoot, and then move them to a cooler place. After about 6 weeks, when the shoots are about 2.5cm long the potatoes will be ready for planting.
Plant in a trench, or in individual holes in a row about 4in (10cm) deep, and cover with another 2.5cm (1in) of soil. Plant your seed potatoes between March and May - planting the first and second earlies about a month before your maincrop. First and second earlies should be planted 30cm (12in) apart (with 45cm between rows), and maincrops 40cm (15in) apart (with 70cm between rows)
Too much water will generate too much leaf growth at the expense of the root potato, however they do need to be kept moist, and in dry periods they should be watered heavily every two weeks when the flowers forming.
As they grow earth them up using a draw hoe or rake. This will encourage a bigger yield, and prevent the light reaching the potatoes turning them green.
Harvesting your potatoes
Simply lift the plant out of the ground with a fork, and fork the ground over well to find all the potatoes. any left in the ground will grow as a 'volunteer' next year - inevitably always in the wrong place!
Earlies are not suitable for storing and should be used as soon as possible after picking. Maincrop potatoes can be stored in hessian sacks over winter in a frost free place (shed or garage). Dry the potatoes overnight before bagging them, but do not wash them. Store only disease free, blemish free potatoes. A single rotten potato will cause the entire bag to rot.
Whichever varieties you choose, always buy top quality seed potatoes from a reputable merchant. Some plot holders will grow supermarket bought potatoes that are sprouting, but this is not recommended. You will want to make sure that your plot stays disease free, and the best way to maintain this is by making sure you don't introduce the diseases to the plot in the first place.
There are a number of considerations when choosing which potato varieties to grow. The first question is what sort of potatoes do you eat? Do you prefer a waxy salad potato, or do you only ever roast potatoes, or mash perhaps. It may be that you do all the above, and in which case you could either grow several different varieties or select a good all purpose variety.
You also need to consider whether you will want to grow enough to store and use all year round. If so look for varieties that store well... If you just want to eat them in season, then pick your favourites, and grow some earlies and some main season potatoes.
Not all varieties are suitable for growing in every region, so ask fellow allotment holders which varieties work best on your site. If you have a problem with blight, then choose some blight resistant varieties, or perhaps slugs are the problem... choose ones that are more resilient to slug damage.
The best course of action is to make a list of what you want, and then scour the seed catalogues over winter and pick the varieties that best match your requirements. Finally have some fun, why not try some traditional and unusual varieties alongside your main crop - you will soon find varieties that are best for you and the plot!
Potatoes Pests and Problems
Common Potato Scab - Raised scabs on the potatoes. This is not usually a major problem. the potatoes are still good to use and just remove the scabs by peeling. This is usually caused in dry summers, on a very light soil. You can help prevent this by watering well in dry periods. Don't put any of the peelings back on the compost though as this will compound the problem next year.
Potato Blight - This is by far the biggest problem potato growers encounter - and if you get it you must act fast, else it will spread to all your neighbours plots and can spread by up to 30 miles in the wind. It manifests itself as mould on the tubers and the leaves. If caught quickly then remove any infected leaves and either burn them, bury them deeply, or take them down to the council recycling facilities. NEVER add any of these to your allotment, or leave them lying around! To prevent blight in the first place consider growing blight resistant varieties, and you can also spray the crop regularly with copper sulphate sprays such as 'Bordeaux mixture'
Slugs - Slugs are always a problem. Use slug pellets, beer traps, or the new biological controls available (Or like me go down with a torch at 11pm and pick them off by hand and kill them)