Although it is not absolutely necessary to chit potatoes as you plant them, it gives them a head start on potatoes which have not been chitted and in turn will give you a slightly earlier and bigger harvest.
Commercial growers don't bother chitting potatoes as it would be too time consuming to do. Instead they keep them dormant in cold storage just under 4 degrees (C) and then plant out when the soil warms up to around 6-7 degrees.
If you are completely new to growing potatoes, you might want to try both chitting and non chitting to see how they fare and record your results later in the summer.
Where you live will probably affect when you decide to chit your seed potatoes and subsequently plant them out. This is due to some areas being more prone to the risk of late frosts. The potatoes will need 4 to 6 weeks of chitting before they are ready to plant. This will give them a chance to sprout and start putting on growth.
You can start chitting potatoes from late January onwards ready for planting in mid-March to April or when soil temperatures reach about 6-10 degrees. The warmer the temperature the better, as they will not do well in cold, wet soil.
Seed potatoes are potatoes specifically sold for planting, rather than cooking and eating. You can buy them from your local garden centre or nursery in small bags or sacks. You can also order the type you like online.
Step 1 - Arrange seed potatoes for chitting
Open your bag of seed potatoes and check none of them are damaged or mouldy. You are now ready to start chitting!
The best method is to place the seed potatoes in seed trays or egg boxes, carefully placing one seed potato in each compartment of the tray or box.
Make sure the rose end is facing upwards. This is the blunt end with the most ‘eyes’, which will form sprouts or shoots. The heel of the potato should be sitting in the box. The heel is the narrow end of the potato where it was cut from the vine.
If you don't have an empty egg box, you can use any container with dividers or make some out of cardboard that give each potato a little space. It is important to let some air circulate between the seed potatoes otherwise they may become damp and mouldy.
Step 2 - Label potato seeds and find a location for them
Carefully label your seed potatoes (name of variety and date) before placing them in a light, dry room, or a greenhouse with a cool to warm ambient temperature, between 7-12 degrees.
A porch or windowsill would also be a good location. The ideal temperature for chitting seed potatoes needs to be cool but nowhere near freezing otherwise they will be damaged. Make sure they are not subject to high temperatures i.e. in a centrally heated room as this will cause the seed potatoes to shrivel.
Too little light and the sprouts will be long, spindly, and liable to break off. Ideally you want short, stubby sprouts which are deep green, almost purple in colour. Indirect light for the entire day is the best way to achieve healthy sprouts when chitting seed potatoes.
Step 3 - Remove shoots except large ones (optional)
If you would like to grow large potatoes, take a seed potato when the new shoots are about 1-2cm high, (which can take around two to three weeks), and rub off most of the shoots.
Leave 3 or 4 of the largest, strongest shoots. Each of these will grow to be a large potato. If you would prefer to have a crop of smaller potatoes, you don't need to rub off the excess shoots.
Step 4 - Aftercare
Regularly check your chitting seed potatoes to make sure they are developing healthy shoots and are not being exposed to too much heat, light, or moisture. Adjust the conditions as required and remove any potatoes which may have gone mouldy as this could affect healthy ones.
After about 4-6 weeks your chitted potatoes should be ready to plant out.
Maincrop potatoes tend to be larger, and grow well in the ground, but early or salad potatoes will do well in containers. You can buy special polypropylene potato growing bags which are designed especially for this purpose and are handy if you are short of growing space. However, you can also plant potatoes in old compost bags and get the same results.
Homegrown potatoes do well in all types of soil, but the richer the better, so dig in plenty of well-rotted organic matter, such as garden compost. You might also like to add a layer of ripped up newspaper to the trench, which can help retain moisture in a dry spell. An open, sunny site is best.
Plant early seed potatoes and salad types in March. Plant them in trenches at least 12cm deep and 30cm apart, with 60cm between rows. Plant maincrop potatoes later, in April. These need to stay in the ground longer and require more space to produce a decent crop. Plant them 12cm deep and 38cm apart, with 75cm between rows.
Remember to place the rose side facing upwards. Take care not to damage the delicate new shoots when backfilling with soil. As the soil warms up, growth develops at a brisk rate producing many new young potatoes.