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Organic Gardening:

How to grow organic Potatoes

by Frann Leach

You should get several pounds from each plant

Potatoes

Solanum tuberosum

Family: Solanaceae (Group 9)

Potatoes are divided into first and second earlies ('new potatoes') and maincrop. They also come in various colours, the most commonly available being white, yellow and pink or red.

Potatoes are often recommended as a good crop for 'cleaning' the ground. The reason for this is that in preparing the soil, you will eliminate much of the weeds, and many of the pests resident in the soil will attack the potatoes, so that when you harvest them, you will remove them at the same time. You often see rows of potatoes growing on established allotments, but unless you are growing one of the more expensive varieties, there seems little point in investing the amount of work involved, as they are so cheap in the shops.

Recommended cultivars

First earlies
Arran Pilot	White	Heavy cropper best in light soil
Maris Bard	White	Very early. Scan and virus resistant
Pentland Javelin	White	Heavy cropper. Scab and eelworm resistant
Duke of York	Yellow	Any soil type or area. Excellent flavour
Second earlies
Maris Piper	White	Good flavour. Scab and blight resistant. Does not like dry soil
Wilja	Yellow	Heavy cropper. Reliable
Nadine	White	Very resistant to eelworm. Good flavour
Maincrop
Majestic	White	An old variety, good for chips (fries)
King Edward	Cream	Well known for its quality
Desirée	Pink	Very heavy cropper. Drought resistant
Stemstar	Cream	Heavy cropper, slug resistant. Good for exhibition
Pink Fir Apple	Pink	A waxy, gourmet variety, but yields are low

First earlies mature in about 100-110 days, second earlies in 110-120 days, and maincrop in 125-140 days. To avoid virus disease, use only certified seed potatoes purchased annually or once-grown seed. To avoid the build-up of soil-borne pests and diseases use a minimum rotation of 3 years for earlies, 5 years for maincrop.

Site/soil

Potatoes need an open site, avoiding frost pockets, and will tolerate light shade. They grow best in deep, fertile, well drained but moisture retaining soil; pH 5-6 preferred. The heaviest yields are obtained from well cultivated soil; add plenty of manure and a general fertiliser such as Growmore 100% organic at 60gm/sq m (2oz/sq yard) the autumn before planting.

Chitting

Sprout or chit potatoes before planting by standing egg-sized tubers on end in boxes of peat or recycled egg boxes in a light, frost-free place. Start earlies in mid-January, mancrop from early February. As shoots start to develop keep a close watch for aphids.

Planting and general care

Plant in a drill 8-15cm (3-6") deep, covering each tuber with about 2.5cm (1") soil. Earlies go in around mid March 30cm by 45cm (12"x18") apart, maincrop from April to May at a spacing of 37cm by 67cm (15"x27"). Close planting of small tubers in June and July will give a late crop of new potatoes.

For traditionally planted crops, protect with soil or straw if frost is expected. Earth up by drawing up soil to near the tops of shoots when large enough, top dressing first. If soil is very dry, moisten first.

To avoid earthing up, cover with black plastic, after watering in if necessary. When haulms push up against the plastic, cut slits in the plastic and pull them through.

Container grown potatoes

The minimum recommended size of container is a 30cm (12") pot, though some people use dustbins (trash cans) or even black plastic bags - in either case, it's important to make adequate drainage holes. For a 30cm (12") pot, put 2 tubers on 10cm (4") soil and cover with a further 10cm (4") soil. When the haulm is 15cm (6") tall, add another 10cm (4") soil and continue like this until plants are within 5cm (2") of the rim. Plants will need watering in dry weather. Feed once or twice with seaweed extract.

Watering

Earlies should be watered every 10-14 days in dry weather at 3-4 gallons/sq yard. Maincrops need a single watering of 4-5 gallons/sq yard when tubers reach marble size.

Harvest

Dig earlies as required, first earlies June to July, second earlies July to August when the flowers open, or for the highest yield, when the foliage dies down.

Dig maincrop from August for immediate use. Those to be stored should be left until September or October when the haulm dies down. Cut haulms and remove to the compost heap (so long as there is no blight visible), wait 10-14 days and lift on a good drying day. Leave tubers to dry off for several hours before placing in store.

Make sure the entire crop is harvested, down to the smallest tuber, to avoid problems with 'volunteers' harbouring soil-borne pests in future years.

Pests and Diseases

Viruses affecting potatoes are many and varied. The regular use of certified seed grown in northern areas will ensure that tubers are virtually free of aphid-transmitted viruses at planting time. Several varieties of potato are resistant to one or more viruses.

Colorado beetle and larva

Colorado beetles are yellow, with black stripes, the larvae are pinkie red. If found in the British Isles, you are legally bound to notify the Ministry of Agriculture immediately, who will take care of the infestation for you.

Potato cyst eelworm: Haulm dies back early, small white, yellow or brown cysts on roots, poor crops, small tubers. Do not use site for Solanaceae for at least 6 years.

Aphids must be controlled to prevent virus infections. Use Derris spray or fatty acid spray.

Potato blight is extremely common in wet years. A fortnightly spray with Bordeaux mixture may prevent or reduce the problem. If plants are still badly affected in late August, cut the haulms and burn them immediately. Harvest after 10-14 days in the usual way.

Common scab is most severe on light, sandy alkaline soil, especially after hot dry summers. Serious attacks often occur on newly cultivated grassland. Do not apply lime to scab-infested land. Apply 3 bucketsful of grass mowings per square yard and dig in to light soils where you suspect a humus deficiency. If you find you have a problem with this disease, there are several resistant varieties available.

Potato wart disease is a notifiable disease in the UK, which must by law be reported to Ministry of Agriculture officials. It may remain undetected until tubers are dug, but occasionally greeny-yellow cauliflower-like growths may occur on stem bases or other parts close to soil level. The tubers become entirely warty and knobbly or develop whitish warty outgrowths which later blacken and decay. Symptoms are more severe in wet conditions and may be so slight as to be overlooked in dry seasons, although outgrowths can arise on tubers after some time in store.

If you're interested in healthy food, you may also be interested in our sister site, The Health Site, Your Online Health Channel.

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