Potatoes are a half hardy crop that originate from South America and first reached these shores around 1586. Being half hardy means that frost can cause problems. It can kill off newly emerged shoots from an early planted crop or damage tubers (potatoes) if the harvest is left too late.
The crop is grown from tubers; you can use your own but it’s probably best to buy fresh seed annually that is certified free of disease. Seed about the size of a hen’s egg is ideal. These should be planted whole, but in the event of larger seed being used, they may be cut into two sets. The tubers can be directly planted into the soil but it’s advantageous to sprout them first as they will emerge more quickly and mature earlier. Buy your certified seed in February or March and place them upright in a tray placed in a light, cool, frost free place. After a month or so the tubers will have developed short (about 12 mm long), sturdy, dark green sprouts.
Potatoes can be divided into 3 types in order of harvest: Early (June), Second Early (July-August) and Maincrop (September-October). The usual time for planting potatoes is March and April. Don’t be tempted to go too early – ideally soil temperatures should around 7°C for three days before planting. Check the Met Eireann website first for the weekly agricultural report for your area – Forecasts > Agricultural Data Report. If you are inland where frost might be an issue don’t plant before mid-March. Early potatoes are planted in March. If well sprouted potatoes planted at this time they should be ready for use during June and July. Main crops are planted in April to early May.
Potatoes are traditionally grown in ridges or drills. Why? The edible portion of a potato is not a root but a stem tuber. Branch stems that grow underground develop from axillary buds of the basal leaves, and towards their tips they swell to form tubers. This explains why we earth up the growing potato plant to cover those axillary buds, which will in due course grow out as underground stems and end up as a crop of potatoes.
Space the drills 70 cm apart for early and second early varieties and 75 cm for maincrop. Using a garden line to guide you, dig out a shallow trench with a shovel, and spread compost/manure (if you have it) and fertiliser along the base. Space the tubers out 25 cm apart in the row for earlies and 30 cm for maincrop. Open up a second drill parallel to the first and cover in the first trench with the soil from the second as you go along. Continue across the plot until you are finished to leave the ground roughly level.
The crop will require to be earthed up as it grows during the early part of the season. As mentioned, potatoes are prone to frost damage and if the shoots are showing and frost is forecast cover the exposed shoots with soil from between the rows. Ridge them up again when the emerged shoots are about 20 cm high. You need a soil covering over the top of the tuber of 10-12 cm for earlies and 15-17 cm for main crop. If necessary first loosen the soil between the rows with a hoe and then use a shovel to earth up.
If you are growing on beds potatoes can be planted on the flat. Dig over the bed, rake it level and plant the tubers using a trowel. Space them 30x30 cm at a depth to give a soil covering suggested above. If spacing them at this distance use smaller seed with 2-3 shoots per tuber. When planted on the flat there is no need to earth up unless planted shallower than recommended. What makes for a good potato crop? A fertile soil with a full leaf canopy by the end of May to mid-June; and the development of a deep extensive root system which is important for water uptake. And keep potato blight at bay.
Slugs: if you find you crop riddled with holes along with hollowed out cavities the chances are that slugs are the culprit. The problem tends to be field or plot specific – it’s a problem in certain fields but not in others. Slug attack tends to worse in wet years on heavy soils and varieties vary in their susceptibility. Varieties like Kerr’s Pink, Maris Piper and Rooster are vulnerable; Golden Wonder, Nicola and Pentland Dell are among the least susceptible varieties. Two slug species are implicated: the keeled slug and the garden slug. The problem with trying to counter the keeled slug is that it lives mostly underground and only comes to the surface to mate. Because of this applying slug pellets may be of limited use. Slugs will feed on tubers from late summer into the autumn; and essentially the longer you leave the tubers in the ground the greater the damage. For example in a trial they discovered that Maris Piper lifted on August 8th suffered 10% damage, lifted on October 3rd 30% damage and lifted in early November 45% were damaged.
The following suggestions may help:
- Grow early or second early varieties as they are harvested early and hence less susceptible to slugs.
- For main crops apply two applications of slug pellets in mid-July and August. Alternatively use four half-rate applications.
- Consider the use of Nemaslug in early August; this is a species of eelworm that actively seeks out slugs and kills them. But it’s not cheap and not 100% effective.
- Avoid growing susceptible varieties.
- If you do notice slug damage towards the end of the season lift the crop promptly as the damage will only get worse the longer the crop is in the ground.
- Do not get alarmed if you notice slug damage to the potato leaves as there is little if any connection between foliar and tuber damage; different species involved in both.
Harvest the earlies and second earlies direct from the drill when they are big enough and as you require them. The main crop haulm will naturally die back in the autumn allowing the crop to be lifted in October. If you wish you can cut the haulm off 3 weeks prior to lifting. Yields can be very variable but you get about 1-2 kg of tubers per plant. Store the crop in a dark, frost free shed.
Early: Home Guard, Duke of York, Coleen, Sharpe’s Express
Second Early: British Queen, Maris Peer, Charlotte
Maincrop: Orla, Kerr’s Pink, Rooster, Record, Pink Fir Apple, Cara, Setanta, Sante, Carolus, Sarpo Mira, Sarpo Axona (Axona is better flavoured than Mira).
For online information on varieties consult the AHDB Potato Variety Database.
Slugs, aphids, wireworm, eelworm
Potato blight, black leg, pink rot, soft rot, dry rot