The variety determines time of harvest, tuber size, flavour and skin colour. Plants that grow white flowers generally grow pale tubers, while plants with coloured flowers grow pink-skinned tubers. There are now over 5,000 varieties, of which I mention only a few to highlight some of the differences.

The three listings of First, Second and Main refer to the speed of growth and maturity date. The boundary between the three is not precise, for example I would class Casablanca as a First/Second Early type.

Within the three types is a loose sub-division of salad potatoes, which are smaller and with firm, waxy flesh. Examples are Anya, Pink Fir Apple and Ratte. Sometimes Charlotte is called a salad potato, because of its waxy flesh.

1. First Earlies grow rapidly in spring and finish by early summer. They can be grown as a ‘catch crop’ before other vegetables, such as kale, carrots, beetroot and celery.

Harvest them slightly immature, as soon as leaves start to yellow – the flavour is ‘newest’ and sweetest at this moment. Do not try to store them through winter because they often start to sprout by autumn.

For sheer quantity in June, Casablanca is superb, although flavour is average. It continues growing for longer than some First Earlies, with a high yield by solstice time.

Swift is rapid as a First Early but a little watery in texture. Worth it for earliness!

Rocket is less rapid, smaller and waxier.

Blue Danube is an early Sarpo, a pretty colour but of average flavour I thought.

Yukon Gold, bred in 1960s Canada, has great flavour and a strong yellow colour after cooking – large tubers have a starchy texture.

Mayan Gold, by contrast, is a heritage variety for small and dark yellow potatoes, with nutty flavours and a floury texture. However, they turn mushy if you boil them for more than about five minutes!

2. Second Earlies mature in midsummer and can yield highly, they also store reasonably well. There is still time to grow many other vegetables, immediately after their harvest.

• For areas with damp summers, Second Earlies are worth growing as a ‘Maincrop’, because they do most growing before late blight arrives and store well.

Charlotte offers a large harvest with fine flavour and firm texture, not floury. It tastes almost as good in March from a sack, as in July from the ground.

Wilja and Estima, both from Holland, give high harvests of decent flavour – Estima is waxy.

Apache is a small, beautifully coloured and waxy Second Early.

Nicola excels in taste tests – it is a salad type, with pale skin.

Harlequin is a rose-skinned Second Early, with small long tubers, a creamy flesh and fine flavour.

3. Maincrops mature late summer to early autumn, with high yields thanks to their long growing period. However, there is more risk of late blight after midsummer, which can prevent them from growing right to maturity, reducing the harvest and possibly damaging potatoes with blight spores, such that they won’t store.

Lady Balfour has had publicity for its blight resistance, but I found the flavour unimpressive, and it suffers blight in any bad year.

King Edward is esteemed for its great flavour and is pretty, with rose-coloured eyes, but the yield may be average.

Desiree is another classic English Maincrop with an excellent flavour and dense texture, red-skinned, but this variety is susceptible to scab.

Pink Fir Apple is a red Maincrop of small tubers with excellent flavour, fiddly to clean because of their knobbly shape.

Ratte is a tasty and small Maincrop salad type.

Sarpo varieties resist late blight but occupy a lot of space with their long stems. At the end of August, those need cutting off when still green, to stop plants from growing any more. Otherwise the tubers become starchy and with less flavour; harvest in late summer before this happens.

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You often hear it said that potatoes are good at suppressing weeds. It’s true that their vigorous growth and dense leaf cover results in fewer weeds germinating and growing. However, they don’t magically clear any thick growth of weeds.

Ground preparation is about feeding soil organisms, providing a soft surface for developing potatoes and mulching weeds if currently present, or maintaining a weed-free surface. This can be easily achieved by adding a layer of compost on top, and/or a cover of plastic or cardboard under the compost, if perennial weeds are established.

• Potato roots do not need loose soil to grow in and develop well in undisturbed soil, which may even be clay.
• Potato tubers need loose soil or compost to swell in because they are soft and watery and cannot push against firm materials.

Potatoes are the only vegetable in my two-bed comparison to give higher harvests in dug soil.

• The increase is small in relation to the time and effort needed.
• Second harvests after the potatoes were lower on the dig bed.

The total harvests from these two beds, from 2013 to 2020, were 754.81 kg/1664 lb from the dig bed, and 854.53 kg/1884 lb from the no dig bed.

For potatoes, the compost used can be less perfect than, say, for carrots, because potato seeds are large and can push roots into places where carrots would struggle to grow. This validates the statement that potatoes are good at clearing ground. Not that they do, but growing them gives us the chance to do two things at once:

1. Smother and clean ground of weeds, with mulches.
2. Have an excellent harvest of food.

Thanks to no dig, you can grow potatoes on any soil from clay to sand. Then there is the question of rotation, and the common advice to wait three years between growing potatoes in the same ground.

I run a trial where we have reached the sixth consecutive year of growing potatoes in the same bed. The results have surprised me so far, with harvests similar now to when we began. There is no increase in disease.

The trial has three strips as described in the table. Each strip has six beds, so there are six beds that run across the three strips.

• Each bed grows different vegetables.
• In some beds I grow the same vegetables every year, to learn about the necessity or otherwise of rotation.
• In the potato beds, we transplant leeks every year as soon as the potato harvest is finished – see Lesson 19.

The only downside of continuous potato cropping, that I have noticed, is the regrowth of volunteer potatoes in early spring. They are tubers left in the ground from a previous harvest. In a way they are free seed; however, if several grow close together your harvest will be lots of tiny potatoes. Hence we remove them.

To find volunteer potatoes, watch for new shoots in early spring, then use a trowel to lever them out. They are often the deepest potatoes that were undiscovered at harvest.

Old-fashioned methods include digging a trench to place seed potatoes in. It’s easier and quicker to use a trowel – see below.

• First shoots appear in 15–25 days, depending on the type of potato and soil warmth.

Chit, or not

Chits are new shoots or sprouts, whose growth is powered by only the potato. It’s often said that seed potatoes with chits will grow more quickly than potatoes planted without any.  I find that any difference in growth is small, but potatoes grow best when sprouts/chits are short and strong.

Keep seed potatoes in light after the new year begins, so that their sprouts stay compact and sturdy. In contrast, seed potatoes in the darkness of a bag grow long and thin sprouts, often damaged when planting.

Potato size

Seed potatoes can be any size, but ideally should be about the size of a large egg, not smaller, as harvest would then be less, from growth starting more slowly. If you are short of seed at planting time, you can cut larger ones in half lengthwise as long as there are at least two sprouts on each half.

First Earlies with fewer chits grow medium-sized rather than small potatoes, in their short time of growth.

For Second Earlies and Maincrop, don’t remove any sprouts and use medium-sized potatoes.

Planting time

You can plant potatoes from early spring, as the soil starts to warm. However, the key factor in deciding when to plant is your last frost date. You need to know this average date for your area.

For example, at Homeacres in 2020, potatoes planted even as late as mid-April grew large quickly in unusually warm weather. Then suddenly, on 11th May, a cold NE wind dropped the day temperature by 7 °C/13 °F, compared to the day before. On the following night, my potato plants lost many leaves to frost. The amount of damage depended on how much fleece I had managed to cover them with. We had three nights with temperatures as low as -2 °C/28 °F.

• Homeacres’ last frost date is 16th May, so I was not surprised. We were still in gain, because we managed to protect most growth with fleece covers.
• Plant First Earlies up to seven weeks before the last frost date, as long as you are prepared for spring frosts with covers (which can be any material, including large pieces of cardboard).
• Plant Second Earlies and Maincrops two to four weeks before the last frost date.

Late planting

You can plant potatoes in late summer for harvests of new potatoes in late autumn, though this would not work with any potato harvested during that summer – you need to set a few seeds by from the spring planting, preferably Second Earlies. Keep them on a windowsill through spring and summer, where they will grow sprouts slowly.

However, leaves are at a high risk of blight, then perhaps of frost, and harvests are small.

How to plant

Plant them the right way up! You can usually see a top, with the most chits, and the bottom with few. Also, the bottom has an indent where last year’s stolon was feeding into it.

Insert a trowel vertically into the ground, to its full length, then pull the surface compost and soil towards you. This makes a slit into which your seed potato can drop. The top is about 5 cm/2 in below surface level.

• For First Earlies, this planting depth means no subsequent earthing up is needed. For Second Earlies and Maincrops, you will need to do some, because the larger number of developing potatoes push upwards.
• If planting through a polythene mulch, first cut two 10 cm/4 in slits at right angles, to make a cross at each plant hole. Use a trowel as above, and slide the seed potato down. After a few weeks, check that the new shoots have found light as they grow upwards, through the slitted hole.

Spacing

Plants can be more or less equidistant, rather than in a line or ridge. Space First Earlies at 30 cm/12 in, Second Earlies at 40–45cm/16–18 in, and Maincrops at up to 60 cm/24 in.

How often

In temperate climates, it’s unlikely that you need to water for the first six to eight weeks of growth. Watering is needed when you see flowers, but only if conditions are dry at that time.

Water, say, twice a week, and give a decent amount.  

Stop watering when more than about 10% of leaves are yellowing, meaning that plants are maturing and making little new growth.

How much

Potatoes are fast-growing plants, with a large surface area of leaves. Therefore they can transpire a lot of water, especially in the last third of their life. They are big plants, and the days are warm as they mature.

Check the soil after you finish watering, to see how moist it is. You may be surprised by a relative dryness. For the last two to three weeks of growth, give plenty of water in dry weather to bulk up the harvest.

This is partly about clearing weeds, and links back to ground preparation you will already need to have done, according to whether there were weeds to smother. It also relates to earthing up, and whether there are developing potatoes to keep in the dark.

Suitable materials include black polythene, grass clippings, straw and sheep wool.

• Remember that undecomposed mulches offer habitat for slugs, which may damage potatoes and also make it more difficult to succeed with transplants for the following harvest.
• Nonetheless, potatoes often grow a worthwhile harvest under mulches like straw and polythene, which would cause slug and growth problems for other vegetables.

Earthing up, mostly Second Early and Maincrop

You need to keep light off developing tubers because they jostle upwards when short of space, through swelling close together. If new white tubers are exposed to light for more than about three days, they turn green with solanine, which is mildly poisonous and tastes bad.

For best results, drop a shovel of compost on top of each plant. It ‘rains down’ through leaves and stems, to land on the rising potatoes and keep them in darkness.

• Usually First Earlies do not need earthing up, because they finish growing before there are enough tubers to push each other up to light.
• Compared to the other mulches listed above, compost is easier to resow and replant into, once you finish harvesting potatoes.

How to judge readiness

Your choice of a harvest date reflects your food preference. Do you want an early harvest with the flavour of new potatoes? Or is your priority a maximum yield? A third consideration is when you want ground ready for succession planting

1. Earliness and flavour

• In early summer, while leaves are green on First Earlies, you can rummage near the surface and pull one or two tubers from each plant, leaving the rest to grow more. They are an early treat.
• If well grown but still with leaves all green, pull First Early plants from late May, for a few small and sweet tubers – quality not quantity.
• First Earlies in particular do not always flower, so don’t wait for that as a cue!

2. Biggest harvest

With Second Earlies and Maincrops, the largest harvests are once you see the leaves turning paler. Often this is two weeks after any flowers fade, with up to a quarter of the leaves actually yellowing.

Once growth is slowing, there is no advantage to leaving potatoes in the ground – pests may eat them and some surface ones turn green. Potatoes rot when frozen, so they must be harvested before first frost.

How to harvest

One option is firstly to remove top growth, by cutting through all stems just above ground level. You can put all of this material, and any other wastes from potato growing and cooking, onto your compost heap.

• There are false statements about composting potato waste material – it’s all good to compost, including blighted material.
• It does not spread disease, nor does it cause a problem of regrowth next spring, from pieces of potato that are supposedly living.

Find your potatoes by pulling the stems gently upwards, all at the same time, to reveal many tubers in the soft surface. Some varieties grow tubers on stolons further away from the main stems; in sandy soils, they may develop downwards and need a trowel.

Rub lumps of soil and compost from the potatoes. Then, if you will be eating them within a few days, clean them – place them all in a bucket of water and rub gently with a soft brush, or swill them around with your hand. They clean easily and very quickly at this point, when fresh.

Storing

Dirty potatoes keep better than washed ones. For long-term storage, after rubbing off excess soil, place potatoes where the skins can dry. This may even be in full sun for a day or two, which is not long enough for skins to go green.

The drying process is called curing, and allows a slight hardening of skins which results in better storage. Place the dry potatoes in paper sacks, of two or preferably three-ply thickness to exclude all light.

Sacks of dried potatoes do not need to be stored somewhere cool for the first weeks or months after harvest. How long you can easily store potatoes, before they sprout a lot, depends on the variety, because each has genetic information that determines its dormancy period, whether short or long, after which sprouting begins.

Here are examples from Homeacres:

• With potatoes we harvest in midsummer, then store in the brick shed where temperatures are 15–20 °C/60’s °F, I see no sprouting or deterioration at this level of relative warmth in late summer to mid-autumn.
• During winter in the same shed, the temperatures are below 10 °C/50 °F, cool enough to slow any growth of new sprouts.
• Each variety stores for a different length of time, and Maincrops mostly store for longest.

Saving seed

It is said that you should buy seed every year and not plant potatoes from your own harvest. As far as I can tell, the main concern is potato virus. If your plants had suffered this virus, you would know – see ‘Diseases’ below.

Despite this, I recommend you save potatoes to replant. These can even be green ones which you cannot eat.

• If, in late winter, you have some potatoes in sacks, for seed but with long sprouts on, it’s fine to knock off those fragile sprouts and then put your potatoes in full light. Then they make a second generation of short chits by the time of transplanting.

Frost

Potato leaves are damaged by the slightest frost. This matters in springtime, when fortunately it is rare to suffer any hard frost which might kill plants outright.

Frost is a potential problem, mainly for early potatoes – any damage to leaves and stems results in a smaller and later harvest, depending on the level of damage. Protect plants with any of fleece, cardboard and paper, draped on leaves in the afternoon or evening before frost is forecast.

• Common dates for late frosts in Northern Europe are 12th–14th May, days known as the Ice Saints days.

Slugs

If slugs are numerous, they make holes in tubers at all stages of growth. Should slugs be a common issue in your garden, I would not grow potatoes through mulches of straw, cardboard or polythene. Use compost only, plus:

• Harvest as soon as the leaves start to fade, rather than leaving them in the soil to harvest later.
• Reduce habitat close to your vegetables, including any decomposing wooden bed sides.

Potato cyst nematodes (Globodera rostochiensis and pallida)

These cause damage in overworked soils – too much cultivation and potatoes often grown in the same piece of ground, as one might find in many allotments. They feed on potato roots, not the tubers; the result is weak growth and yellowing leaves.

• The best remedy is to rotate! Allow three to four years before growing potatoes again in the affected soil.
• No dig, with a 4 in/10 cm mulch of organic matter, will start a healing process in damaged soils that are often full of pests.

Wireworms (Agriotes spp.)

The slender white and wiry grubs, up to 3 cm/1.2 in long, can be a serious pest. However, they are not common and mostly occur where there was recently grass, or close to grass edges.

They are the larvae of click beetles, and have an unfortunately long life in soil – up to five years. They mostly eat root vegetables, including potatoes, carrots, onions and beetroot, but also tomatoes. They eventually pupate one summer, before hatching into beetles.

Cultivation is supposed to reduce their numbers, by disrupting habitat such as weed roots, and exposing the wireworm to bird predation. However, I know a grower who cultivated fields for six years and was still experiencing significant damage at the end of that time. He will have caused a lot of soil damage too, at no little expense.

• Trapping in spring is the best remedy. For example, place potato halves face down on the soil, check the following morning to see if wireworms have gathered there, and then collect them up.

Weedkiller

Pyralid weedkillers are growth hormone disruptors, which interfere with plant processes to confuse growth, resulting in deformity and sometimes plant death. They are a problem resulting from corporate power and ineffective legislation.

Most damage is to the growing tips of plants. If you suspect this, check for deformity there.

Avoidance is difficult because of the weedkiller’s unseen presence in many composts and compost products, and also in hay. There is more to say about this – do check my video. I am just mentioning enough to warn you, as sadly it is very damaging to potato plants. You would notice curling inwards of the newest leaves – see the photos below.

Clopyralids are common in lawn herbicides, from where they accumulate in commercial composting facilities where lawn clippings have been added to the mix. They are also in some potting composts.

Late blight (Phytopthora infestans)

This is the main disease threat for tomatoes and potatoes. It arrives during summer, when night temperatures stay above 10 °C/50 °F for 48 hours, and air humidity is above 90% for all of that time.

This level of warmth and moisture enables growth of newly arriving blight spores. They are widespread in such conditions. Potato leaves quickly turn translucent brown, followed by dark spots appearing on stems and potato tubers.

In cooler and especially in dry summers, blight is unlikely to be a problem. Blight warnings are sometimes issued by manufacturers of fungicide when there is no need to worry. Often there is more worry than blight.

However, in warm and damp conditions, watch the health of your potato leaves and get busy when you see any sudden browning or limp leaves.

1. Cut off all infected foliage and stems. If weather is wet all the time, best cut the plant to ground level. You can put this material on the compost heap because blight spores do not survive in soil or compost, only on living material.
2. Check that the cut stems are fresh green and not brown; if the latter, potatoes may be rotting already. If cut stems are green, leave for two to three days so that any blight spores on the soil die. Then pull your potatoes and put them somewhere to dry – perhaps in a box in the sun for a day or two – before placing them in paper sacks.

• Check the potatoes a week later, to remove any rotten ones. Eat them quickly if some are rotting because that suggests the blight managed to enter many tubers, and they will not keep for long.

Potato virus  

This is seed-borne and rare, because most seed grows healthy potato plants. The main symptoms are bright yellow or curling leaves, with yellow veins.

I keep my own seed and this works fine. Just be vigilant, because potato virus is a main reason quoted for not replanting your own potatoes. If you suffer it, best dispose of plants and buy new potato seed next winter.

Scab (Spongospora subterranea – cercozoa, or Streptomyces scabies – bacteria)

These organisms live in many soils. You see corky lesions which may become dry, brown pustules on potato skin. Fortunately, the damage is skin deep and can be peeled off before cooking.

Scab is more common in alkaline soils and in dry summers. It is relatively rare on tubers developing in compost, while parent plants are rooting into soil. Therefore ‘earthing up’ with compost, and no dig in general, are good precautions against it.

Blackleg (Dickeya solani)

This arrives as blackleg bacteria in seed potatoes and fortunately is rare – stems turn black and slimy near ground level. As soon as you see this, it’s best to remove all of the plant and some of the infected soil, and bin it.

If blackleg bacteria are left in the soil after removing infected plants, they may cause trouble next summer. However the bacteria mostly develop in very warm weather, so are rare in areas of cooler summers.

Clear

After the harvest your soil should be clear of weeds, just remove any that are still there. Be sure to remove every last little potato, which would otherwise regrow in autumn or the following spring.

Use a foot to re-firm the surface, then rake level. You are now ready to replant.