Things you might need to know about growing potatoes
This page isn't a 'guide to growing potatoes' - every gardening book or website has them. It's the background information which makes sense of all those instructions!
You may already have heard that potatoes have been cultivated in South America for thousands of years, by the Incas and their neighbours. The varieties we grow are only a tiny fraction of those grown in the Andes; it's rather as if there was a country where the only rose grown was 'Peace'. Our traditional potatoes have limited genetic diversity which makes them more vulnerable to disease. Breeders are constantly trying to build in disease-resistance, by going back to the genetic kaleidoscope of native varieties. A new variety, Sarpo, has bred-in resistance to blight.
For a fascinating article about inca potatoes, with photos of some of the wacky-looking varieties, click here!
For a fascinating article about inca potatoes, with photos of some of the wacky-looking varieties, click here!
Once we know where potatoes grow in the wild, it is easier to understand more about them. They are naturally plants of the forest floor, where they grow in leaf litter and the moist, humus-rich woodland soil. We can understand how their habit of spreading by tubers, and growing upwards through the soil above them, would help them in these surroundings. The tubers keep the plant alive, under the warmth of the soil, through the colder months. No wonder potatoes don't like lime; their woodland soil would naturally be acidic.
So why do we grow potatoes in ridges?
As potatoes naturally grow upwards through the leaves accumulating on top of them, we will get the best crop by putting them in low and piling soil above. The traditional method of puttig them in the ground and 'earthing them up' does this, but it is only one way. You can grow a very heavy crop in a small space using bags. These don't have to be purpose-made, any stout bags with holes for drainage will do. Other people use plastic dustbins or piles of old tyres. The main thing is that you put your seed potatoes in near the bottom, and as the leaves grow, gradually add more compost to get the plant to grow upwards. All your crop is produced above the original 'seed' potato.
You can use bought compost, but because of their natural preferences, potatoes will grow very happily in the rougher stuff from your compost heap! At the end of the season everything gets tipped out and the compost can be used for soil improvement.
You can use bought compost, but because of their natural preferences, potatoes will grow very happily in the rougher stuff from your compost heap! At the end of the season everything gets tipped out and the compost can be used for soil improvement.
What is the reason for 'chitting' potatoes
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Gardeners will tell you that you have to 'chit' seed potatoes prior to planting. This involves putting them end-up (ideally with the eyes uppermost) in trays in a cool, light but frost-free place, from when you buy them till when you plant them. They will probably tell you that this will speed up the crop. In fact trials by the RHS have found it makes very little difference.
Left: seed potatoes chitting, as per tradition, in the spare room |
The main reason for standing potatoes out in the light like this seems to be to stop them from doing what they do in your vegetable rack - producing long wangly white shoots that would break off when you tried to plant them.
Some keen gardeners do start their potatoes off growing early, however. In a waterproof tray, lay layers of crumpled up newspaper. Soak this in dilute plant food. lay the seed potatoes on this, with them on their sides, and they'll start to root into the soft paper. By the time you're ready to plant them their root system is already developing. I confess I've tried this, and it worked, but I didn't notice the spuds were ready much earlier.
Some keen gardeners do start their potatoes off growing early, however. In a waterproof tray, lay layers of crumpled up newspaper. Soak this in dilute plant food. lay the seed potatoes on this, with them on their sides, and they'll start to root into the soft paper. By the time you're ready to plant them their root system is already developing. I confess I've tried this, and it worked, but I didn't notice the spuds were ready much earlier.
Why can't I just plant potatoes from the supermarket?
Why must I buy 'seed' potatoes at vast expense?
Simple answer: Seed potatoes are grown in conditions where they won't get infested by aphids (usually in cool conditions, which is why our seed potatoes are grown in Scotland). Aphids carry Potato Virus. You really, really don't want potato virus. Once you get it in your soil you can't grow potatoes there for at least 7 years. Which will really mess up your crop rotation plans!
If you're growing potatoes in a bag or bin, you CAN use supermarket potatoes - as long as you spread the used compost out somewhere like fruit bushes, well away from future potato crops!
This year I've just been told that unused seed potatoes can be stored, without deteriorating, for 12 months in the fridge. The allotmenteers who've tried this are going to report back at the end of the season on how they performed.
If you're growing potatoes in a bag or bin, you CAN use supermarket potatoes - as long as you spread the used compost out somewhere like fruit bushes, well away from future potato crops!
This year I've just been told that unused seed potatoes can be stored, without deteriorating, for 12 months in the fridge. The allotmenteers who've tried this are going to report back at the end of the season on how they performed.
What do I need to know about blight? It all seems very complicated.
Blight is a fungus disease which afflicts potatoes - and indeed tomatoes - in cool damp conditions. Is is spread in the wind and rain, and the spores can also lurk in home-made compost or even the soil. It attacks the leaves first, but if left unchecked it then spreads to the potato tubers. They don't seem too bad when you lift them, but when stored they rot to a foul-smelling slimy mess.
Here in the South-East our generally hotter dryer summers mean blight is less often a problem. Watch out for trouble when we get a wet mild summer. Examine your plants as often as possible, looking for small light-tan blotches on the leaves, or blackish, wet patches which appear as if scalded (which go light tan when they dry off). This is the usual first sign of blight and you should act fast. A delay will give the fungus time to reach the tubers. Cut the foliage off all affected plants. If the crop is nearly mature, cut off all the foliage anyway. Give the potatoes a couple of days or so to mature their skins then lift them. You will get a reduced crop but if you leave the leaves on you'll get NO crop.
Store your tubers in hessian sacks (if you need to exclude more light, use two doubled up) to allow the air to circulate and reduce the risk of rotting in storage. This is, from experience, definitely better than using paper sacks.
A specialist service, 'blightwatch', helps professional and amateur growers by warning when blight is around in their area.
Click here to go to the 'blightwatch' page.
To reduce the risk of getting clobbered by blight, grow a good 'second early' variety like Wilja, instead of a maincrop like Cara. Because the potatoes mature earlier, they are out of the ground earlier and thus less at risk.
Here in the South-East our generally hotter dryer summers mean blight is less often a problem. Watch out for trouble when we get a wet mild summer. Examine your plants as often as possible, looking for small light-tan blotches on the leaves, or blackish, wet patches which appear as if scalded (which go light tan when they dry off). This is the usual first sign of blight and you should act fast. A delay will give the fungus time to reach the tubers. Cut the foliage off all affected plants. If the crop is nearly mature, cut off all the foliage anyway. Give the potatoes a couple of days or so to mature their skins then lift them. You will get a reduced crop but if you leave the leaves on you'll get NO crop.
Store your tubers in hessian sacks (if you need to exclude more light, use two doubled up) to allow the air to circulate and reduce the risk of rotting in storage. This is, from experience, definitely better than using paper sacks.
A specialist service, 'blightwatch', helps professional and amateur growers by warning when blight is around in their area.
Click here to go to the 'blightwatch' page.
To reduce the risk of getting clobbered by blight, grow a good 'second early' variety like Wilja, instead of a maincrop like Cara. Because the potatoes mature earlier, they are out of the ground earlier and thus less at risk.
What about slug damage?
Ah! slugs. Yes . . . You may see some varieties listed as 'slug resistant', notably 'Kestrel'. Our experience has found that the reason they do not attrract slugs is that they have little flavour. Other gardeners don't agree - your choice. We would recommend trial and error, as every site is different. If you find a variety is particularly vulnerable then next year, choose a different one. If you find another variety is pretty good, let us know! We'll add it to this advice page.
To reduce slug damage, do use pellets - we strongly recommend 'Growing Success rain-proof slug pellets', which contain a different chemical to the other brands and are much more effective, especially in damp weather (and no disgusting mess to clean up either!). The other thing you must do is avoid leaving them in the ground any longer than strictly necessary. Lift the crop as soon as it's ready, and inspect the tubers carefully before stroing them. Any damaged ones should be used straight away. As with blight, you will get less problems if you grow a good 'second early', which is out of the ground quicker, than if you grow maincrop varieties.
To reduce slug damage, do use pellets - we strongly recommend 'Growing Success rain-proof slug pellets', which contain a different chemical to the other brands and are much more effective, especially in damp weather (and no disgusting mess to clean up either!). The other thing you must do is avoid leaving them in the ground any longer than strictly necessary. Lift the crop as soon as it's ready, and inspect the tubers carefully before stroing them. Any damaged ones should be used straight away. As with blight, you will get less problems if you grow a good 'second early', which is out of the ground quicker, than if you grow maincrop varieties.
