To grow potatoes you need to buy seed potatoes which are guaranteed virus free, rather than use old potatoes from your fridge or left over from last year’s crop. The reason for this is that potatoes are prone to diseases, and although you may get away with it for a year or two you are sure to store up trouble for yourself in the long run. The potato plant propagates asexually by producing more potatoes which are storage organs (tubers). If left in the ground over winter any that survive go on to produce new potato plants. As they are simple vegetative clones once they develop diseases they can pass these on from year to year too. We prevent this disease cycle by growing them from certified disease free stock (seed potatoes). Many of these are grown in Scotland where the acidic peat soil and cold winters discourage the development of viral and other diseases. Anyway, seed potatoes are relatively cheap so there is no excuse!
You want to start planting out your potatoes from late March, but any time up to the end of April is usually fine. You will need you seed potatoes from about 4 weeks before this to start them off (chitting).
Chitting is the process of encouraging potatoes to form strong shoots prior to planting. It is said that this will lead to more potatoes in the long run, but I have not actually tried planting potatoes without chitting, so I can’t vouch for this! Simply place your seed potatoes in an egg box or other suitable tray, with the eye end uppermost (if you look carefully at a potato you will see that it has more eyes at one end than the other). Leave them in a bright place for a few weeks until they have formed good strong sprouts about 1in (3cm) long. They should look dense strong and dark coloured – quite different to the weak anaemic straggly shoots that form on potatoes left in the dark too long.
2. Prepare the bed
In the weeks waiting for you seeds to chit, get the bed ready. Deeply dug soil is best, so the shoots that grow from the potato stems. If yours is heavy or hard give it a really good digging over to about 12in (30cm) or more deep. Potatoes do not like manure or lime, but incorporate compost if the soil is lacking in organic matter, or sand or charcoal fines is the soil is hard to make it more friable.
Next create trenches, digging the soil up into mounds either side. Trenches should be about 2ft apart. In the photo you can see I have made two short 4ft trenches across one end of a bed. (I used to plant four 8ft rows but our family are eating less carbs these days!).
3. Warming the soil
Potatoes need a warm soil to get growing quickly. Too cold and damp and they can sulk or rot away. So place fleece, black plastic or corrugated plastic (as in the photo), over the trenches so that the sun can warm the deep soil. You need to do this even if recent weather has been fine and warm because it takes months for the deeper soil to warm up.
4. Laying out
Once your potato tubers have chitted, remove the plastic you have laid over the trenches. Lay out your chitted seed potatoes in the bottom of your trench, spacing them about 6-8in (15-20cm) apart for first earlies (new potatoes), 9-12in (27-30cm) apart for second earlies or main crop. The purpose of laying them out is that it is easier to adjust them to get them spaced evenly at this stage rather than when some have been planted.
Using a trowel to dig a hole 6 to 8in (15-20cm) deep and plant each of the potatoes in the position you have determined. Ensure the tuber is the right way up. Cover them with a couple of inches of soil (5cm), but do not fill up the hole in one go. We want to encourage leaves to break the surface soon to start photosynthesis.
6. Cover them up again
Water them in if the soil is dry, then put back the protection to warm the soil further and protect them from the worst of the spring cold. This will help them get off to a good start.
Check for signs of shoots emerging every week. It will take a while, be patient…
Eventually you will see shoots pushing their way up above soil. Let them get about 6 to 8 in high (15-20cm) then they need earthing-up.
This simply means heaping soil around them until the stem is buried and only the top leaves are above the soil. The purpose of earthing-up is to ensure that there is a maximum amount of stem below ground. It is from the stem that new tubers are produced. Earthing up helps to produce the greatest amount of tubers per plant.
This photo shows the same potato shoot once it had been earthed-up.
This process needs repeating every few weeks as the potato plants grow. Eventually, the trenches you originally dug become ridges and the ridges become trenches as earthing up proceeds. At that point earthing up stops and the plants continue to grow.
8. Looking after the crop
Potatoes need adequate water, so keep them irrigated if the weather is dry. Check the leaves regularly for signs of disease.
By June your potato plants will be growing quickly. Potato plants grow quite tall, 3ft (90cm) or so, as you can see in this 2008 photo. I use stakes and string to keep them in place otherwise they tend to sprawl.
10. Harvest – the good news!
This is great fun, like unearthing buried treasure! If you have got this far you deserve it.
When it is time to harvest your crop (1st earlies ~June, 2nd Earlies ~July/August, main crop ~Sep/Oct), carefully dig from one end of the row, lifting soil with a garden fork. Work with care, and any you prang with the fork put aside for immediate use – they won’t keep. Try not to leave any behind – they can be a nuisance or sourse of disease next year.
With first earlies it is better to just dig up a few at a time, so you can eat them immediately – they don’t keep well and are just magic taken from earth to plate in under an hour. The rest will keep growing happily and getting a little bigger each day.
For second earlies and especially main crop that you intend to store, place them on a bench in the sun (or on the ground if dry) to dry for a few days – this helps the skin harden and improves their keeping qualities. Remove any that are damaged or diseased and either bin them or eat them soon. Brush off any dry loose soil, and store the good ones in sacks or trays. I separate them in layers with newspaper, so that if one starts to rot it does not infect the others so readily. Store them in a cool frost-free place – a shed or garage, in the dark. Check them over every now and then, and remove any that are deteriorating promptly. They should keep until late April, unless you eat them all before!
11. Diseases – the bad news!
This section really comes between growing and harvest, but I didn’t want to spoil the joy of harvest, so I’ve placed it at the end.
Although potatoes are considered an easy crops to grow, the increasing prevalence of Blight can make many varieties all but impossible in bad years. So, keep an eye out for diseases and take action quickly if you think you have problems. Yellowing leaves, low down on the plant are not a sign of disease on their own – some yellowing is inevitable – they are simply lacking light and getting old. The commonest potato problem you need to know about is Blight, both early and late varieties.