Certification

Seed potatoes can only be grown in field which have been tested and shown to be free of PCN eelworm (see Pests & Diseases), and which have not grown potatoes for many years. Details of certification schemes are complex and vary from one country to another.
Basically, seed potatoes start off as a completely disease-free stock (e.g. as laboratory grown microplants) and go through a sequential scheme, where every year of field growth leads to a slightly lower grade. Government inspectors look at growing crops systematically and judge any visual symptoms of disorders against set criteria, with back-up laboratory assistance, as required. Depending on the results of their findings, they will award the grade applied for, downgrade of fail each crop.

There are 3 EU grades of seed potatoes, which we in the UK call

• EEC1  UK equivalents are VTSC1 and VTSC2
• EEC2 UK equivalents are Super Elites 1, 2 & 3 and Elites 1, 2 & 3
• EEC3  UK equivalents are AA
• English CC is a lower graded than those detailed above and does not qualify for EU grading. It should only be used in very limited circumstances.

Certification does not end with the field inspections! Once the crops have been harvested, they must be graded to set standards, depending on the grade attained after field inspection. Before each consignment of seed potatoes can leave the farm of growth, they must have a plant passport label, issued by the certifying authority and they must be inspected by a governmental inspector. Only when they meet all the criteria are they certified as seed potatoes.

Check the label on your seed potatoes – it should be an EU Plant Passport, showing the certification number, grade, size, certifying authority and many other details. Be very suspicious if labels are not present or if the label claims to be a world-wide passport (there is no such thing).

Certified Seed Potatoes

Saving money by not buying certified seed potatoes is, in most cases, short sighted. Low grades, table potatoes and garden grown seed potatoes carry more spores of bacteria and fungal pests than high grade certified seed potatoes. In addition, non-certified seed can carry PCN eelworm (see Pests & Diseases), or can be treated with sprout suppressant.

Chitting

This process allows strong, green chits (sprouts) to develop on the tuber before planting. Dormant or just sprouted seed potatoes can be set up in trays with the sprout end (rose end) facing upwards. Place in a frost-free, light area e.g. the windowsill of an unheated room, as the warmer the room the faster the process. It is generally agreed that chitting is recommended for First Early varieties as it gives the tubers a faster start and the crops will reach a useable size slightly earlier.
If apical dominance is encouraged during chitting, by removing all side shoots and just leaving the rose end sprouts, the growing plant will produce fewer, but larger tubers (ideal for producing a crop of baking potatoes). If all sprouting shoots are left on the tuber, the growing plant will produce more numerous, but smaller tubers (ideal for First Earlies and Salads).
The full situation is however more complex and the technical description – “premature ageing” – gives an indication of this. Chitting does speed thing up in the beginning, but it also speeds up the onset of senescence (the natural dying-off of foliage), therefore potential yields can be reduced. This is not a problem with First Earlies, as these crops are lifted as soon as they are ready. This also applies to some Second Early and Salad varieties. Chitting Maincrop varieties is not really essential, although if sprouting has started anyway this process will keep them in best condition as it is possible to manipulate tuber numbers against size.

Microplants

Under current legislation it is not possible to certify seed potato varieties for sale unless they are on the current National List or the EU Common Catalogue. Many heritage varieties are not, therefore the legal only way to access these varieties is to purchase disease-free microplants that have been produced in licensed laboratories.
Microplants are produced using the same process that is used to produce the very highest grade seed potatoes. They are grown on in jiffys and are despatched in protective blister packs during early June. Careful production, using for example, disease free compost and an aphid barrier can result in a crop of “seed” potatoes.  The clean tubers can be planted the following season to achieve a larger crop. It is only recommended that you do this once, as repeated garden growth means that the tubers can pick up all sorts of bacterial, fungus and worst of all PCN eelworm (see Pests & Diseases).
The production of Microplants allows Gardeners access to unusual and interesting heritage varieties which otherwise are not available.

Christmas Potatoes

Also called “Second-Cropping”, these are seed potatoes that have been held in specialised cool storage since they were harvested. They are normally despatched during late June / July, when they should be planted immediately. By following our Growing Tips & Harvest Hints, a crop of fresh potatoes can be harvested much later than normal, and in time for Christmas dinner, if you wish.

Back to Tips & Guides