The climate in Northern Ireland is frequently mild, damp and totally conducive to potato blight !
Despite this, or perhaps because of it, potatoes are relatively easy to grow organically and whilst the effort required can be considerable, the freshness and flavour make it all seem worthwhile. If space is not limited then it is quite possible to grow potatoes for use the whole year round, otherwise grow a few earlies for summer use; a few plants could even be grown in tubs !
Site & soil
Fortunately, potatoes are really not too fussy, provided the soil is free-draining but moisture retentive. Plenty of organic matter, well incorporated will both feed the crop and hold moisture, helping also to prevent common scab.
Higher soil pH's (above 5.8) should be avoided if common scab is likely to be a serious problem (as on light soils) and liming should take place in the rotation after potatoes and not before.
To avoid the ravages of Potato Cyst Nematode (eelworm/PCN) never grow potatoes on the same piece of ground more than once in 5 years. If you do get eelworm then try a resistant variety or stop growing potatoes altogether as yield will go down and down very rapidly.
Cultivation, planting & ridging
The ground should be well dug over prior to planting and plenty of organic matter incorporated. Potatoes are a good crop for breaking new ground as the deep digging or double digging required breaks up ground well and allows you to remove perennial weeds such as scutch (couch grass). There is then further digging when the crop is lifted !
Digging the ground during winter allows the frost to assist in forming a good soil crumb structure (particularly on clay soils), but can lead to loss of nitrogen by leaching (washing out) in wet areas.
A mulch of manure or compost after digging, plus a covering of polythene or old carpet etc, can help prevent leaching. If this is not possible then dig and manure in the early spring.
If your supply of organic matter (manure or compost) is limited then dig it into the bottom of shallow furrows, place the seed potatoes on top and build soil ridges over them. Once the tops are about 2 inches tall make the final ridges with a draw hoe so that the tubers new have plenty of soil covering them.
In the Northern Ireland climate, unless you are on a frost-free site, plant earlies in March/April and maincrops from the 3rd week in April onwards; slightly later if late frosts are likely (I had a severe frost in the 3rd week in June in 1997 ! )
A 24-28" wide row is suitable (two 24" rows will fit a 4 bed). Plant earlies at a 12" spacing and maincrop at about 10".
If larger potatoes are required for baking then space the setts 2" wider apart.
For smaller potatoes reduce spacing by 2". Avoid close spacing in varieties which produce large numbers of tubers eg Kerr's Pink and Maris Piper.
Seed selection and chitting
Choose seed potatoes carefully. Always buy certified seed as it is much healthier, and to be truly organic avoid seed which has had fungicide dressings. If seed potatoes look as if they have had sprouts removed then reject them. Small seed tubers about the size of a hens egg are the best value but if only larger seed tubers are available then it is best not to cut them in half before planting as the risk of rotting is high.
In Northern Ireland's short growing season, crops grown from chitted (sprouted) seed potatoes emerge, grow and mature much more quickly; by as much as 3 weeks.
Earlies should be set to chit in the light early in the year, preferably before they start to sprout. The aim is to get 2 or three shoots only at planting time.
With maincrops seed should be stored as cool as possible (without frosting) until mid-March. Seed should then be boxed up and placed in a light position so as to get several short, strong, green sprouts at planting time.
Additional feeding will help to give a heavier crop and good cooking quality. This is best provided by a mulch of manure, compost or comfrey leaves. Liquid feeding and watering are really too much trouble for potatoes unless the summer is very dry.
After thorough seedbed preparation, earthing up (ridging) should remove most of the weeds, but some hand weeding may be necessary up until the tops meet across the rows, after which the tops will normally suppress most weeds.
The biggest problem will probably be slugs. To avoid problems potatoes should be lifted once the skins are set and not left in the ground. If slugs are a perpetual problem then try a variety which is known to be less susceptible to them.
Wireworms and possibly leatherjackets may be a problem in ground freshly broken from grass. This will normally have disappeared by the time potatoes are next grown in the same place.
With the local climate blight can be a serious problem. It appears as dark, spreading spots on the top of the leaves with a faint whitish growth underneath. It is incurable and prevention is the best bet. Bordeaux mixture, the only organically allowed chemical spray, applied carefully (do not over-spray) protects the foliage. However, this may be disallowed for commercial organic farmers at the end of March 2001, and may then become difficult to obtain.
If a bad blight attack occurs, cut the tops off and remove them as immediately. Leave the potatoes in the ground for at least 3-4 weeks and then lift them. The tubers must also be sorted very carefully before storing them.
If crop loss is often severe then growing only earlies will help to reduce losses.
Harvesting and storage
Always lift potatoes on a dry day. Do not store damaged or diseased potatoes. Store as cool as possible without getting them frosted. Store in paper or natural hessian bags in the dark. Avoid car exhaust fumes.
Growing in deep beds
Either 2 rows along the bed or three staggered rows are possible, but two rows are easier to manage. Varieties which produce tubers right at the top of the plant (eg Maris Piper, Navan, Sharpe's Express) will require good mulching to prevent greening of the tubers as earthing up is less easy in beds than it is in rows. Dense tops may need supporting to keep paths clear.
Some of the popular garden potato varieties grown in Northern Ireland are very old, going back to the last century ! and others are fairly new. Everyone has their own favourite varieties, but the following are suggested for growing in Northern Ireland (dates show when the variety was introduced) :
Traditional First Early varieties :
Home Guard (1942) - Very early, floury texture for an early
Sharpes Express (1901) - Later, very floury texture if left to mature, when it is best baked. Yield suffers in dry weather so keep well watered
Dunluce (1976) - Slightly earlier than Home Guard, locally bred
Traditional Second Early varieties :
British Queen (1894) - Very floury, good tuber shape, prone to blackleg
Ballydoon (1931) - An old favourite, but poor yield
Traditional Maincrop varieties:
Arran Victory (1918) - Purple skin (known as 'blues') and deep eyes, floury, tubers can be small, healthy seed essential
Kerr's Pink (1917) - Known as 'Pinks', deep eyes, floury, lots of tubers so plant at wider spacing; very blight susceptible
King Edward (1902) - Excellent all rounder, very blight susceptible
Pentland Dell (1960) - Chipper and general purpose; seed must be chitted . Now being replaced by Navan
Dunbar Standard (1936) - Good all rounder, tall foliage
Golden Wonder (1906) - Very floury, russet skin, pear shaped & poor yield, but excellent flavour; late maturing
Record (1944) - Dutch variety, flavoursome, floury yellow flesh; commercially grown for crisps
Other Maincrop varieties:
Pentland Squire (1970) - Good baker, closer spacing essential to avoid hollow tubers
Navan (1987) - Locally bred, good all-rounder and replacement for Pentland Dell. Eelworm resistant, but susceptible to slugs. Keep well ridged to avoid greening of tubers
Maris Piper (1963) - Good all-rounder, a parent of Navan. Keep well ridged to avoid greening of tubers
Cara (1976) - Less floury, good cooking quality, good baker, late maturing, chitting essential
Spey - well shaped with a shallow pink eye, slightly russet skin and a good flavour, but prone to common scab. Yield suffers in dry weather so keep well watered
Salad potatoes :
Pink Fir Apple (1880) - Waxy, Terrible shape !
Varieties with reasonable resistance to potato blight :
Sante - (maincrop) widely grown by organic farmers
Remarka - (maincrop) grown by some organic farmers, very prone to common scab
Stirling - (maincrop) possibly the most blight resistant, prone to harvest damage
Varieties with some resistance to potato blight :
Cultra - (maincrop) widely grown but can get severe blight
Brodick - (maincrop) foliage very resistant to blight, tubers slightly less so
Brodie - (late maincrop) tubers very resistant to blight, foliage less so
Estima (second early) - some blight resistance
Colleen (first early) - possibly the most resistant first early
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