How to grow Irish potato

Pick a field that has not grown potato, tomato, pepper, eggplant or tobacco for 3–4 years — these are all one family and share the same soil diseases.

Avoid any land where potatoes wilted and died green before — bacterial wilt stays in that soil for years. If you must use it, never save seed from it.

Choose a well-drained spot that does not flood — waterlogged soil rots seed and tubers and helps wilt spread.

Good crops to grow before potato are cereals (maize, wheat) or a grass fallow — they starve the potato diseases out of the soil.

Put it in your plan now to buy certified seed and start sprouting (chitting) it 2–4 weeks before you plant.

Buy certified seed tubers from a registered dealer or seed scheme — with a label, the variety name and this season's grade. Certified means grown to be free of blight, wilt and virus.

Choose egg-sized tubers, about 35–55 mm — between a large marble and a small hen's egg. That size is plenty; you do not need big ones.

Buy enough — potato is planted thickly, about 2–2.5 tonnes for a hectare (far more by weight than a grain crop). Your recommendation gives the amount for your field.

Buy a high-potassium basal (planting) fertiliser (a compound rich in K) — potato eats more potassium than any other nutrient. Get the amount in your recommendation.

Store seed tubers cool, light and airy (light keeps sprouts short and green); store fertiliser dry, off the floor, and away from food, water and children.

Start 2–4 weeks before planting. Spread the seed tubers in a single layer — a shallow box, tray or old egg-crates work well — so light reaches every one.

Keep them somewhere cool, airy and light — out of direct sun, but not dark and not hot. A dark place gives long, weak, white sprouts that snap off.

Set each tuber with the eye-end up — the end with the most little eyes — because that is where the strongest sprouts come from.

Wait until each tuber has short, sturdy, green or purple sprouts about a finger-joint long. Short and stubby is what you want; long and pale is too weak.

As you handle them, throw out any tuber that is soft, rotting, shrivelled or leaking — plant only firm, healthy seed.

Only lime if a soil test — or past crops that stayed yellow and stunted even with fertiliser — shows your soil is very sour. Potato handles mild acidity better than most crops.

Where scab has pitted your skins before, keep the soil on the sour side and go easy on lime — heavy liming makes scab worse.

If you do lime, spread it evenly over the field like sprinkling flour, then work it into the topsoil with a hoe — lime left lying on top does almost nothing.

Lime weeks before planting (it acts slowly), and keep it separate from manure — do not apply lime and manure on the same day.

Work in your basal fertiliser as the ridges go up, so the young plants find food straight away — your recommendation gives the type and amount.

Dig or plough the land deep and loose — about 20–30 cm (a spade's depth or more). Potatoes cannot swell in hard, cloddy soil.

Break up the clods until the soil is crumbly — loose soil grows smooth, well-shaped tubers.

Work in well-rotted manure or compost (dark, crumbly, no strong smell) — about a wheelbarrow every few strides. Never use fresh, raw manure.

Draw the soil up into ridges about a stride apart (≈75 cm), tall and loose — each ridge is one planting row.

Make sure water can drain off between the ridges; potato hates sitting in wet soil.

Plant when the soil is moist but not wet, and only once the frost is past — potato shoots are killed by frost.

Set each sprouted seed tuber on the ridge with the sprouts pointing up, about a hand-width deep (≈10 cm).

Space the seed a hand-span plus a thumb apart (≈28 cm) down the row — that is a full hand-span and then a thumb's width more — with rows a stride apart (≈75 cm). This gives roughly the plant population your yield needs.

If you must cut big seed, leave each piece (sett) with 1–2 eyes and let the cut faces dry and heal for a day or two before planting, or they rot in the soil.

Band the basal fertiliser to the side of the seed, a hand's width away and a little below — never touching the tuber, or it burns the sprouts.

Cover and firm the ridge over seed and fertiliser so the tuber sits snug in moist soil and comes up strongly.

Walk the crop twice a week (more in warm weather) from the day the first shoots break ground, looking down each ridge.

Cutworms: look for young shoots cut clean off at ground level, worst in the morning. Scratch the soil near a cut plant to find the fat, grey, curled caterpillar and squash it.

Bacterial wilt: look for a plant that wilts in the heat of the day but stays green (not yellowing). Cut a stem and stand it in clear water — milky threads streaming out mean wilt.

Rogue any wilt plant at once: dig it out with the soil around it, carry it out of the field, and do not plant that spot again this season.

Count the gaps (stations with no plant) as they come up, so you know how even your stand is.

If you find wilt → rogue it out and wash your hands and tools before touching healthy plants, so you do not carry it down the row.

Keep the ridge moist like a wrung-out cloth, not wet — water about every 6–8 days (more often in heat or on sandy ridges), pushing a finger in and watering when the top few centimetres are dry.

Water little and often rather than flooding — soggy ridges rot the seed tubers before they sprout.

Water in the cool of the morning or evening so less is lost to the sun.

Make sure water drains away between the ridges after rain; do not let it pond around the plants.

Walk the crop twice a week — more in cool, wet, misty weather, which is exactly when blight strikes.

Late blight: look on leaves for dark, water-soaked patches, often at the tips and edges, with a white furry mould underneath in the morning damp. It spreads fast.

Early blight: look on the older, lower leaves for brown spots with rings inside them, like a target.

Aphids: turn leaves over and look for clusters of tiny green or black soft insects, and sticky, sooty leaves.

Virus: mark any plant with crinkled, mottled or rolled leaves and stunted growth, and rogue it out so aphids cannot spread it further.

Act at the very first blight lesion — tighten your spray and cut out badly-hit tops; do not wait for it to spread.

Weed early, while the weeds are small and before the canopy closes — hoe shallowly so you do not cut the potato's shallow roots.

When the plants are about knee-high, draw loose soil up around the stems from both sides into a firm, high ridge.

Build the ridge up enough that the tubers forming below are well covered — at least a hand-width of soil over them.

Re-cover any tuber you see poking out, and close any cracks in the ridge — cracks let in the tuber moth and the greening light.

Time the earthing-up to bury your top-dressing at the same time, so the fertiliser feeds the crop and not the weeds.

Apply as the plants reach about knee-high, when the canopy is building and the tubers are about to set.

Use a high-potassium compound (your recommendation gives the type and amount) — potato needs far more K than N or P. Potato also answers to magnesium (Mg): on sandy soils, or where you kept lime low to dodge scab, choose a compound that carries Mg too, or add a little magnesium sulphate (Epsom salts).

Band it along the row a hand's width to the side of the plants, not on top of them.

Cover it with the earthing-up soil in the same job, so rain does not wash it away and it reaches the roots.

Apply onto moist soil (after a weeding or light rain), and keep the grains off wet leaves — they stick and scorch.

Start a protectant fungicide (such as mancozeb) as the canopy closes — before you see any blight.

Spray on a calendar every 7–10 days, and tighten to every 5–7 days in cool, wet, blight weather.

Wet the whole plant — the tops and the undersides of the leaves — until just before it drips; blight starts on the parts you miss.

Re-spray if rain falls within a few hours — the protection washes off.

At the first lesion, switch to a systemic blight product — one that is taken up inside the leaf and can knock back blight that has already started (such as metalaxyl, usually sold mixed with mancozeb), where a protectant only guards the clean surface it lands on. Tighten the interval, and cut out and carry away badly-hit tops.

Spray safely: cover your skin, nose and eyes, spray in the cool with the wind at your back, keep it off food, and wash well afterwards. Respect the days-to-harvest (the pre-harvest interval) on the label — the least number of days you must wait between your last spray and lifting or eating the tubers.

Keep the soil evenly moist down to where the roots and stolons are — water every 6–8 days, more often in heat.

Check with a finger: water when the top few centimetres are dry, before the plants wilt.

Water in the cool of the day and let the leaves dry before nightfall, to give blight less chance.

Keep the ridges draining — do not let water stand around the stems.

Walk the crop twice a week, more in cool wet weather, right through bulking.

Late blight: keep checking leaves for dark water-soaked patches with white mould underneath; now also look at any tuber you uncover for firm brown dents — blight in the tuber rots it in store.

Tuber moth: look for exposed or cracked tubers and shoot-tips with tunnels — the moth lays on any tuber the soil does not cover. Earth them over at once.

Potassium or magnesium shortage: on the older, lower leaves, scorched, browning margins (with undersized tubers) mean potassium is short, while yellowing between the veins with the veins still green means magnesium — make sure the K feed went on, and add a magnesium source if you see the vein-yellowing.

Feel the soil moisture as you walk — even moisture here prevents the cracked, knobbly tubers that come from wet-then-dry swings.

Keep spraying on the same 7–10-day calendar (tighter, 5–7 days, in cool wet weather) with no gaps through bulking.

Always coat the new growth — the youngest leaves are unprotected until you spray them.

At the first lesion, switch to a systemic product — one taken up inside the leaf that can knock back blight already started (such as metalaxyl; a protectant only shields the surface it lands on) — shorten the interval, and remove and carry away badly-hit tops so spores do not wash down to the tubers.

Re-spray after rain washes the cover off, and rotate products so blight cannot get used to one.

Spray safely: cover skin, nose and eyes; spray in the cool with the wind behind you; keep it off food; wash well after; and count the days-to-harvest on the label so the tubers are safe to eat.

Every week or two, walk the rows and look for green shoulders poking out of the ridge and for cracks in the soil.

Draw fresh soil over any exposed tuber straight away — a good covering, a hand-width or more.

Close the cracks in the ridge with soil — cracks let in both the greening light and the egg-laying moth.

Keep the ridge shoulders full right to the end — a well-covered ridge is your best tuber-moth control without any spray.

Keep the soil evenly moist all through bulking — water every 5–7 days, more often in heat or on sandy soil.

Never let the crop dry right out and then flood it — that sudden swing is what cracks tubers and grows knobbly, second-growth potatoes.

Check with a finger before the plants show any stress — water before they wilt, not after.

Water in the cool and let the leaves dry by night, to keep blight down.

Keep the water even and gentle — do not wash the ridges down or expose the tubers.

Stop watering as the tops begin to yellow and die back — the crop is finishing and no longer needs it.

Let the plants die down (or kill the tops — see the next job) so the skins can harden.

Test the skin after a couple of weeks: press a thumb on a tuber and twist — if the skin stays put and does not rub off, it is set and ready to lift.

If the skin still rubs off → wait longer and leave the tubers in the ground a while more before lifting.

About two weeks before lifting, cut or pull the tops off at the base, or slash them down.

Carry the cut tops right out of the field — especially any with blight — do not leave them lying on the ridges over the tubers.

Leave the tubers in the ground those two weeks so the skins finish setting.

If blight is in the tops, remove them promptly so the last spores die off before you dig.

Lift on a dry day when the soil is dry and crumbly — wet soil clings, bruises the tubers and spreads rot.

Dig well to the side of the row with a fork or plough and lift from underneath — driving the fork through the ridge spears the tubers.

Handle them gently — set them into baskets, do not throw or tip them from a height; bruises you cannot see rot later.

Let the lifted tubers dry on the surface for an hour or two, in the shade or gentle sun — never strong midday sun, which greens and cooks them.

Sort as you collect: put aside every tuber that is cut, bruised, green, rotten or diseased, and keep only clean, sound tubers for storage.

Use the damaged and green ones first (they will not keep), and keep any seed-grade tubers separate.

First cure for 1–2 weeks: spread the sound tubers in a single layer in a cool, dark, airy place so the skins harden and cuts heal.

Then move them to a cool, dry, airy store — a dark room, a pit, or a ventilated shed.

Keep them in the dark — cover windows or use a dark store; even a little light over weeks turns eating potatoes green.

Keep the store airy so the tubers do not sweat and rot — do not seal them in a solid heap or a closed sack.

Keep eating (ware) and seed potatoes separate and clearly apart, so you do not eat your seed or plant your food.

Eat the damaged and green ones first — they will not keep — and check the store often for rot, sprouts or tuber-moth holes; pull out any bad tuber before it spreads.