Thanks to John Harrison of Allotment & Gardens
Potatoes are unusual in the vegetable world in that they actually do better with a pH between 5.5 and 6.0 against the preferred 6.5 to 7.0 of most else.
Apart from anything else the somewhat acid soil deters a disease called common scab that likes dry, alkaline conditions.
Because of this potatoes should be grown as the last crop before liming in any crop rotation.
Being a very productive crop, when all goes well, potatoes require a good supply of nutrients, in particular nitrogen and potash along with plenty of water. To retain water in the soil so as to be available on demand, a soil rich in organic matter will perform better than one lacking. The addition of rotted manure prior to planting will add that organic matter as well as provide a good proportion of the nutrient requirement. This is covered in detail in Potato Fertiliser Requirements,
It’s often said that potatoes are a good crop for clearing ground, especially new ground, before planting other vegetables. The truth is that it is the amount of work required to prepare and cultivate the ground for potatoes that clears the ground.
The year starts early for potatoes, in January when you should order your stock of seed potatoes. Although there is such a thing as potato seed, usually only breeders make use of them. Potatoes are grown from seed potatoes which are just small potatoes, about the size of a hen’s egg, saved from the previous year’s crop.
Saving Your Own Seed Potatoes
Most UK seed potatoes are grown in Scotland where disease spreading aphids aren’t around and under strict conditions to avoid spreading disease. You can save tubers from one year to the next but this increases the risk of passing on and strengthening disease. I would suggest you can get away with it for 1 year but then get fresh clean seed for the next.
Planting Supermarket Potatoes
Do not just try and plant potatoes from the supermarket. More often than not you will be wasting your time as they have been inhibited to prevent sprouting although I have had success with some Anya that had started to sprout.
What Variety of Potato to Buy
To help you decide what seed potatoes to order we’ve listed the best potatoes for flavour and chipping, mashing etc. You might want to look up the information on potato blight as well and pick resistant strains as the disease has been so wide spread and virulent in recent years.
First Early, Second Early and Maincrop Potatoes
Potatoes come in three main groups:
- First Early – these are the fast developers who produce new potatoes. Depending on variety they will be ready to harvest between 10 and 12 weeks after planting.
- Second Early – slightly slower these are ready to harvest between 13 and 15 weeks after planting.
- Maincrops – these take anything from 20 weeks for the early maincrop varieties to 26 weeks for late maincrops.
The early varieties produce less per plant and per square metre of ground used but most often miss the blight which is the biggest threat. Many home growers just don’t bother with the maincrops but they are the most productive per plant and for land used. Maincrop potatoes tend to store well so you can be eating your own spuds all year round.
Chitting Potatoes
Chitting is the process of pre-sprouting before planting. Some authorities say it benefits maincrops but not earlies, some say it’s of no benefit and some it is of benefit to all types. My attitude is that nobody says it does any harm to chit potatoes. As the seed tubers are usually with me in January I may as well chit them.
When you get your seed potatoes you put them in a cool but frost free place where they get some light but not direct sunlight. The potatoes will then grow short stubby shoots to get them off to a fast start when planted out. Some people suggest rubbing off all but three shoots to help get larger potatoes with the maincrops.
Planting Out & Cultivating
Check out Potato Fertiliser Program for soil preparation prior to planting.
In the sunny south of the UK you can start planting in early March, mid-March for the Midlands and late March to early April further north. The idea is that the soil has started to warm and by the time the foliage comes through the main frost danger has passed.
To plant you can just make a hole with a trowel and pop the seed potato in or you can draw a trench about 100mm deep and place the potatoes in it. You then pull the soil from the sides to cover the potatoes, producing a ridge.
Standard Spacing For Potato Planting
Your first and second early potatoes should be planted about 30cm apart in rows about 60cm apart. The maincrop, being the heaviest cropper, need a bit more space so plant them about 40cm apart in rows 75cm apart.
In raised beds with early varieties you can plant 30cm apart reducing the row width to 45cm. Below that reduces yield and overcrowding increases the risk of disease problems. Some varieties, e.g. Sarpo Mira, yield well and produce a lot of foliage so increasing their spacing to 60cm in the row and the row spacing to 100cm increases productivity.
Check the individual variety description with the seed merchant.
Earthing Up Potatoes
As the plants grow you need to draw the earth from the sides of your rows over the plants. This process is known as ‘earthing up’ and increases eventual yield and protects from late frosts. It won’t hurt the plants when you cover some of the leaves by earthing up or slow down growth.
Potato Disease, Pests and Problems
- There’s a long list of diseases and pests that can affect potatoes, most of them relatively rare, thankfully. The most devastating problem is potato blight which is covered separately.
- Slugs are a major problem and the use of nematodes is worthwhile as they kill the underground slugs not just the ones on the surface like pellets.
- A dry period followed by wet can result in tubers splitting or even a potato problem called hollow heart so do water well if the weather is fine.
- Wireworm is a problem when planting into land previously used for grass but otherwise not a major problem
- Other problems that are covered include common scab, powdery scab, dry rot and white spots on potatoes
Harvesting & Storing Potatoes
First Early Potatoes
Your first early potatoes should be ready to start harvesting from 10 to 12 weeks after planting. A good sign that there are tubers ready is that plants flower. Potato flowers can range from small and hardly noticeable to bright coloured and striking. Initially don’t expect too heavy a yield, you might not get more than a good meal from the first plant harvested. Just leave the rest of the plants to develop, it’s worth sacrificing a few plants early to get the delicious new potatoes.
Once past 12 weeks you should be looking at just over half a kilogram per plant. Some potatoes grown as earlies will just carry on bulking if left, Orla and International Kidney (Jersey Royals) being examples of potatoes grown as early varieties that are actually maincrops
Second Early & Maincrop Potatoes
The second early varieties like the salad potato Charlotte will take a week or two longer and the main croppers like Desiree and King Edward will be at least another month. Maincrops take between 20 and 26 weeks to reach their potential yield.
If you’re not certain when you planted or if the crop is ready, dig up one or two plants and see. If there are still lots of tiny potatoes on the roots then leave a fortnight or so before seeing what things are like.
With the early crops you want to get them out of the ground as soon as you can to free up the space which there is just time to get some benefit from. I like to follow potatoes on with leeks or a green manure mustard. Leaving them in the ground once developed has no benefits and increases the risk of slug or other damage.
Harvesting Main Crops
With the main crops which are bred to be stored, the haulm should be cut off a week or preferably two weeks prior to harvesting which encourages the protective skin to ‘set’.
Leaving in the soil beyond two weeks has no benefit and just increases the risk of blight, slug or frost damage.
Wait for a nice bright but at least dry day to harvest on. This allows you to dry out the potatoes before storing them.
Approach from the side and carefully insert the fork, levering up to expose the tubers. Spread the crop on some dry ground for a few hours to set the skin and dry them. This will help them store better.
If they are coming up dirty rinse them in a bucket of water before hardening. You don’t want them fully washed, just get the thick off.
Harvesting Blight-Affected Potatoes
If your crop has been hit by late potato blight, your method should be slightly different. Cut of the haulm (foliage) and dispose of appropriately – see potato blight – then leave the crop for 2 to 3 weeks. A scattering of slug pellets on the surface at this point is helpful to reduce slug damage.
The 3 week gap is to reduce the chance of any blight spores landing on the tubers and causing blight in storage.
In really bad blight years, wash each tuber in a bucket but add a couple of drops of washing up liquid. The idea is to wash off any disease spores before storing. It’s not foolproof but it does reduce in-store blight.
Ensure you get even tiny potatoes out of the ground when harvesting or next year they’ll be growing and they will act as a reservoir for pests and disease.