Knowing when to harvest potatoes is based on whether they’re an early potato or maincrop, time in the ground, and what happens to their foliage and flowers
One of the easiest edibles to start off with is the humble potato. They’re relatively low-maintenance, can help cultivate the soil, and will also suppress any weeds that try to compete with them. They’re also very fun to dig up and eat! But when are potatoes ready to harvest? This is probably the most taken for granted kitchen gardening knowledge you’ll find. Seasoned gardeners will ‘just know’ when the plant is ready. When you’re just starting out it’s a bit of a head-scratcher.
The answer lies in which type you’ve planted. The vast majority available will fit into the categories of ‘First Early’, ‘Second Early’, and ‘Maincrop’. Read on to know what to look for when it’s time to harvest potatoes.
In my opinion, the best type of potato to grow is one that fits into the ‘First Early’ category. These include the Red Duke of York, Lady Christl, Arran Pilot, and scores more. This year I’ve grown Pentland Javelin which is a type that matures slightly later than other First Earlies.
‘First Earlies’ are one of the earliest garden crops to mature. You plant them from St Patricks Day to mid-March and then dig them up around 10-12 weeks later. Typically from June to July but sometimes earlier. They’re easy to grow, don’t tend to suffer blight, taste tender and delicious, and fun to dig up in early summer.
Look for potato flowers
The way you tend to know that first earlies are ready is by their flowers. Early potatoes generally produce flower buds that sometimes bloom and sometimes don’t. It’s time to dig up your tender, homegrown potatoes when the buds drop or the flowers that do bloom begin to fade. Another good indication is seeing unopened flower buds dropping from the plant. At this point, the leaves will still be green but some will begin fading to yellow. The potatoes from earlies will be about the size of an egg with skins so tender that they’ll melt in your mouth.
If you’re not sure about if they’re ready, gently dig around a plant and look for potatoes. If they’re the size of an egg or larger, you can start harvesting. First earlies left in the ground will continue to grow. That means that if you’re not quite sure if they’re ready to harvest, just leave them in a little while longer. Not all early potatoes are great for storing but some are, so do your research before you buy potato varieties.
Potatoes that fall into the ‘Second Early’ category include Nicola, Maris Peer, Jazzy, and Kestrel. They differ only in one way from first earlies — they mature about three weeks later.
As for planting times, you can get them in the ground at the same time as first earlies but it’s better to wait. The traditional day to plant them in most of the UK (zone 7-8) is the first day of spring, in late March. Just think about it, if you plant them at least two weeks after your first earlies then the harvests are staggered by five weeks. That gives you time to eat your first crop before another massive harvest is ready.
Use the same indications for harvest as first earlies and look for blossom drop. By the way, how gorgeous are potato flowers? They come in all different colors and potatoes were actually grown in Europe as ornamentals before they were grown as food crops.
Think of a massive baking potato and it’s most likely a maincrop, sometimes called storing potatoes. Varieties in the UK include Cara, King Edward, Pink Fir Apple, and Purple Majesty. In the USA, they’ll be Russet varieties.
Maincrop potatoes are planted at the same time or up to a month later as second early potatoes. They need a lot more time to grow — about 20 weeks. Over the summer they swell and grow resulting in harvests large in both size and quantity.
Though you can harvest many main-crop potatoes as earlies, or carefully dig a few out after the plant has flowered, I think it’s best to grow types specifically bred to be earlies. They’ll crop earlier and be bred for flavor and texture as an early. Leave maincrops to grow into the biggies they’re supposed to and store them for use over the winter.
Harvesting Maincrop Potatoes
You harvest main crops in late summer, typically in August to September and you know the time is right when much of the foliage on all your plants begin to turn yellow. It will then shrivel up and turn brown and dry, and eventually only shriveled leaves and stems will be left. At any time during this process, cut the plant off about an inch from the ground and leave the tubers in the ground for a couple of weeks before digging them up. This helps harden up the skin and makes them better for storing.
This is natural die-back and will be different from a disease. If you see black spots on the foliage or if the die-off is only affecting some of your plants then you should investigate potato diseases. If the issues are happening before the 20-week mark then it’s also an indication that something is wrong.
Unlike early potatoes, you can store maincrops for months at a time. First, you should dry them completely before putting them in bags or boxes for storage. Any wet areas could introduce rot, or actually be rot. Spread them out in a garage or greenhouse, or outside in the sun, turning them over after one side is dry. Leaving potatoes in the sun for any longer than a day or two can cause them to turn green. Small amounts of green are harmless but if a potato turns dark green, you want to avoid eating it.
Store maincrop potatoes in a cool garage or shed and make sure to eat the best ones first. A friend once tried to save the best ones for last but by the time he got to them, the mice had already had their turn. If you’re looking for recipe ideas for larger second earlies, try Hasselback potatoes. With their tender skin, you don’t even have to peel them.