How to Grow Potatoes
Potatoes are one of the easiest vegetables to grow and need limited attention during the growing season. You can choose from many types of potatoes earlies,( a good choice if you suffer from blight,) main crop, salad potatoes, heritage, even blue potatoes. Potatoes are ideal for growing in the veg plot or containers. There is detailed planting advice below, but remember the top growth, called Haulm, is frost sensitive. This means if you have planted early, or the plants have put on spurge and the foliage is above the soil and bad weather is threatened, you will need to protect the top growth from frost.
Once Potatoes are growing and the foliage (haulm) is above the earth, earth up regularly, (see below) water potatoes in dry periods, and feed them, if you have time. If it is a reasonable summer with no blight, potatoes will grow with little attention.
The main problem when growing potatoes is blight, which is described below. Essentially, it is an air-borne fungus which will strike if the conditions are right. Generally, this is a spell when it is warm and damp, and unfortunately there is no real cure for blight.
Best tips when growing potatoes:
- Start with good quality seed potatoes
- Always earth up potatoes even when growing in pots.
- Take great care not to damage the top growth, especially when earthing up
- Water well, potatoes need a good amount of rain to grow well and feed regularly.
- If you live in a blight prone area, see below, grow the blight resistant varieties of Potato.
Chitting Potatoes
In Jan/Feb, some weeks before you are ready to plant out the potatoes, lay them on paper in a light cool room away from direct sunlight to allow the tubers to form shoots, as in image left. Chitting is often the first step to growing potatoes but not essential to a good crop.
Keep the potatoes out of direct sunlight in a cooler area, too much warmth and the shoots will be leggy. Chitting takes around 6 weeks by which time the shoots should be around 2.5cms long.
When to plant potatoes
Plant out "early potatoes", which include the new potato varieties in March/April; "Second earlies" in April; and Maincrop later in April. Potatoes are frost sensitive and need protection.
Potatoes take up a lot of growing space and unless you have a large veg plot, it may be more convenient to save space and grow potatoes in containers.
Potatoes grow well in large containers, place 3 or 4 tubers in each pot with 15-20cms of good compost in the bottom and cover with 10 cms of compost. If you are planting in the vegetable plot, plant the potatoes about 13cms deep and 30cms apart. If you have chitted the potatoes handle carefully so as not to damage the shoot and plant with the shoots upwards, if possible.
It is advisable not to grow potatoes in the same ground each year or where you have grown tomatoes previously (which are the same family, Solanum) because of the risk of blight, which seems to be an increasing problem with wetter summers. Blight causes the foliage to turn yellow and collapse. Potatoes grown earlier in the year are less likely to be effected, which are earlies and salad potatoes.
Ideally, to reduce the risk of disease, if space allows it is better not to grow any of the same veg in the same bed each year. For more information about which vegetables belong to the same family growing group and how to rotate your veg crop, see Crop Rotation.
Earthing up and Haulms
If you plant out early or we have late frosts, you need to protect the top growth, called haulms, from frost. Potatoes are not frost hardy (What does "frost hardy" mean?) As soon as the shoots appear earth up or cover the growth by adding more soil in the pot.
However, frost protection is only one reason for earthing up, it's not the only reason. It is more fundamental. "Earthing up" which means as the top growth appears, extra soil is added to the pot, or scraped up around the potatoes if in the ground, to form a mound and continue with earthing up as the potato grows, (see image left.)
Earthing up increases the depth of soil. The potatoes form under the soil beneath the plant, so a good depth of soil or compost is needed for the potatoes to grow.
If the potatoes are in the veg plot, earth up to create raised ridges up to 30 cms. Earthing up will help to increase crop yields and offer some protection against blight.
It also helps to keep the potatoes in the dark so that the tubers do not become green.
Slug attack
Potatoes can be prone to attack from slugs. These are a type of slug which live in the soil, underground all the year round. This means that slug pellets and other surface barrier methods of slug control are ineffective. To dispose of these types of slugs, it is best to use Nematodes, which are a biological method of slug control watered into the soil. How to use Nematodes.
Potato Blight
Potato Blight is a problem when growing potatoes. Blight is an air bourne fungus type disease which attacks the foliage (and later the tubers) causing it to collapse. It commonly occurs in wet, mild and humid conditions and is difficult to manage. Blight can affect tomatoes as well, although if grown in a greenhouse this will afford protection as it is mainly, but not exclusively, a disease which affects out door crops. Blight starts with brown marks on the leaves, image left and quickly spreads so that all the foliage turns brown or black collapses and the plant looks patently sick; it cannot be missed. Once it takes a hold, there is not much that can be done as it spreads rapidly.
Good air circulation can help. Whenever space allows, do not plant the tubers too close together. In addition, follow crop rotation because the fungus can overwinter in any tubers left in the soil and the virus can spread from there. This is why when clearing the veg plot at the end of the season, it is important to remove all potatoes, including any tiny ones.
You can grow Blight resistant potato varieties, which does not guarantee that Blight will not visit, but much reduces the chances. The most commonly sold Blight resistant varieties is the Sarpo range. Late varieties of potato are more prone to blight. Earlies and salad potatoes may escape as the warmer humid temperatures which are more likely later in the year. In the eastern parts of the UK and drier areas, it is less of a problem, which may be why a lot of potatoes are grown in Lincolnshire. It is the humid, warm air which allows the pathogen to spread, and it can destroy a crop in a couple of weeks.
If the plant becomes badly infected, the only possibility is to cut off all the infected leaves close to soil level and be careful to pick up all bits of infected leaves. If the blight has not reached the tubers, they can still be harvested.
Potatoes also suffer from keeled slugs which live underground and bore into the tubers, which damages them and makes them prone to rotting. Because this form of slugs lives so far underground slug pellets are not effective, nematodes are a better suggestion.
Potatoes can get scab which makes them look unattractive, but they are edible and not noticeable when peeled. This tends to be more of a problem on thin chalky soils, which are prone to drying out the addition of organic matter will reduce the risk of scab.
Suggested potatoes to Grow
Which potatoes to grow is always a question of choice and space. Potatoes take up a lot of room even in containers. There are several different types of Potatoes, first and second earlies, Salad potatoes (harvest June onwards) and Maincrop (harvest later in the season).
Earlies, which as the name suggests mature more quickly, so you can harvest sooner.
Earlies take about 16-17 weeks to mature, maincrop 18-20 but can be left in the ground until October and generally store well.
Earlies are slightly less prone to blight, Maincrop take up more space and for longer so there are advantages each way.
For main crop, when blight is often a problem a good choice would be organic Potato 'Sarpo Mira' in an attempt to beat the blight later in the year. They are said to be one of the most blight resistant potatoes. You may have a personal preference, if not a good starting point is to look at varieties which have the RHS garden merit award
In 2013 the RHS did a trial of first earlies and best early salad potatoes grown in containers. Those varieties which gained or retained the award were: 'Casablanca' a waxy white fleshed potato, 'Golden Nugget' waxy, 'Sharpe's Express', 'Maris Beard' 'Lady Christi' 'Jazzy' 'Vales Emerald' and 'Charlotte' worth checking them out.
Blight resistant varieties : 'Sarpo Mira' (Maincrop) 'Orla' (First early) 'Carolus' (Early Maincrop) 'Athlete ( Second Early)
Planting for Christmas
It is possible to plant potatoes in August for harvesting later in the year for Christmas dinner. Buy seed potatoes sold as Christmas or winter potatoes and they are best grown in containers so you can bring them into a greenhouse, undercover or shelter to protect from frost. These potatoes do not need to be chitted before planting.
Plant into the container in the usual way and the best time is late August /Early September. Use the same type of container and compost as you would normally. Water in dry spells and avoid wetting the leaves, which antagonises the blight around late September/October if it is warm and wet.
The top growth is frost sensitive, protect with a fleece or bring under glass into the greenhouse. These potatoes will be ready to harvest about 12 weeks after planting.
Potatoes are an ideal container crop. As with all container-grown plants or vegetables, because they are in a container, they need a little more attention in terms of watering as they are more vulnerable to drought and drying out.
When to Harvest Potatoes
Check once the plants are flowering. This is a sign the crop is ready. If you have planted in the ground, take care when you harvest not to spear the potatoes with the fork and to clear them all out of the ground, including the tiny ones, to prevent weak seedlings from growing the following year.
Earlies can be lifted as soon as the flowers appear as can salad potatoes.
Maincrop can be left in the ground much longer even after flowering. Towards the end of the season, cut off the top growth from Main crop, leave for about 2 weeks and lift and store somewhere cool and dark. Hessian sacks are good for storage as they allow air circulation. Potatoes need to be stored in a frost free place and it is important to exclude light. It is important the Potatoes are completely dry before storing. Maincrop potatoes will keep and store for longer than earlies.
last updated 01.03.2022