One potato, two potato ...

Now is the right time to plant potatoes, with the weather and the soil finally warming up. Traditionally, gardeners planted their potatoes on Good Friday, which could mean a chilly March start for the tubers, or a warm late April and a race to develop to maturity. This year with the prolonged cold, we’ve had little choice but to wait until the latter half of the month.

The Secret Garden Club planted out its maincrop potatoes this weekend at our annual potato workshop, where we demonstrated not only how to grow in the open ground, but also how to grow them in a restricted space – good for growers with a small garden or only a patio area, maybe.

We concentrate on heritage varieties which are not readily available in the shops. Some of our favourites are:

Pink Fir Apple

Pink Fir Apple was originally imported in 1850 but was unknown in the mainstream for decades, only recently becoming fashionable. The tubers are long and often rather knobbly, which can make them fiddly to peel. (I usually don't bother  and just scrub hard instead.) The skin is part pink, or brownish yellow with distinctly yellow flesh. Although grown as a maincrop for later harvest, the flesh is waxy with a good nutty salad potato flavour.

Red Duke of York

The tubers are large and round with distinctive crimson skin. The floury flesh has a creamy texture and a clear yellow colour, and is very versatile in the kitchen  - it can be boiled, fried, mashed, roasted or chipped. The Duke of York variety has been around since the 19th century but the first red-skinned tuber was discovered in Holland in among a crop of  white skinned potatoes in 1942.

Russet Burbank

A small russet or brown-skinned potato, rather like the russet apple. It has white flesh and holds its shape well in cooking. Originally developed in Lunenburg, Massachusetts, the variety is named after potato grower Luther Burbank). The original Burbank potato was identified in the 1870s; the Russet Burbank, with its rough skin, in 1914.

Yukon Gold

An Central/South American style potato – that very yellow flesh and buttery flavour is characteristic of American potatoes. Today Yukon Gold is mainly available in the US and Canada. Another versatile culinary variety and especially good for baking and mashing.

Salad blue

These unusual potatoes were first grown in Scotland in the 1900s. Both the skin and flesh is a deep indigo, tending towards purple, colour. The name is misleading, as the potato is best used in frying, baking and mashing rather than boiling up for a salad. It has a light, open texture and moist flesh with a mild flavour.  The blue colouring is an anthocyanin, which is an antioxidant, and the colour remains after cooking. Together with Highland Burgundy, below, and a more conventional white-fleshed variety, they make the most fantastic multicoloured chips.

Highland Burgundy

The Highland Burgundy potato is so-called, it's claimed, because it was used to provide an appropriate colour to a meal for the Duke of Burgundy back in 1936. The flesh is crimson or red with a distinct ring of white just below the skin, and the colour stays fast in cooking. The texture of the flesh is drier and denser than that of the Salad Blue, but the Burgundy should be cooked in similar ways: fry, bake, roast or mash, but don't boil.

Having discussed heritage (or heirloom) tomatoes in our previous Secret Garden Club afternoon, it’s interesting to see that there are less rigorous guidelines for a potato to qualify as a heritage variety. A heritage potato is, broadly, one which has been around since before 1950.

After World War II mass production of potatoes was needed to feed the population. Varieties which were high-yielding and reliable croppers were preferred to some of the quirkier, less prolific types, and it's those same potatoes that you find dominating the greengrocer and supermarket shelves today. Many of the potato varieties which had been grown on a small scale before the war became neglected and continued only by a few specialist growers. The growing interest in organic growing and farmers' markets has brought them to public attention again.

There are registered heritage varieties which have been grown for generations: Pink Fir Apple, King Edward, Duke of York and Arran Pilot are examples of these. Then there are non-registered varieties which have also been grown for many decades, often on smaller farms and smallholdings. Varieties such as Salad Blue and Highland Burgundy come into this category.

There is a useful articles on heritage guidelines and varieties on the BBC's gardening blog.

Diner beware

It’s worth pointing out that the tubers are the only part of the potato plant that are not poisonous. Potatoes are a member of the Solanum, or nightshade family, as are tomatoes, aubergines, and, yes, deadly nightshade. When you see your potato plants in flower you’ll see the family resemblance. 

Mayan Gold potato plant in flower.

Potato leaves, flowers and stems are all toxic. If you leave the plant to grow on after flowering, it will grow a small green berry on the central stem, which looks for all the world like a small green tomato. That’s also poisonous. So stick to the tubers, and spare a thought for Lords knows how many ancient Andean foragers who discovered the hard way which parts of the plant could be eaten and which couldn’t.

Growing in the open ground

Growing potatoes in the open ground takes up space. But if you have that space they’re an easy crop to grow. The hard work all comes at the beginning, when you need to get the ground ready for your tubers.

1. Buy seed potatoes to plant. You can try your luck with planting potatoes bought at the supermarket, but there are good reasons not to do this. Potatoes in the shops may have been sprayed with a shoot suppressant. They also may not have been grown in the UK and so won't be well adapted to grow here. Many, if not most, of the seed potatoes grown in the UK come from Scotland and are bred to grow well in our conditions. Seed potatoes should also be guaranteed free from viruses, which culinary potatoes won’t be. 

With seed potatoes you get a huge variety to choose from – we like potatoes from Carroll’s, Thompson & Morgan, and also Sutton’s have a wide variety available.

Salad blue potatoes with 'chits' - the little shoots which have already sprouted.
These give the potatoes a head start once they're planted in the ground.

2. Place your potatoes somewhere light and cool (but not cold – the tubers mustn’t be exposed to frost), like a shed, to ‘chit’. Chits are the growing sprouts that will develop on potatoes stored before they are planted out. There are two good reasons to chit your potatoes: 1) it gives them a head-start when they go into the ground as the growing shoots are already developing, and 2) it will help you to plant them the right way up.

3. When you’re ready to plant out, dig a trench up to eight inches deep for each row of potatoes in your intended bed. Each row needs to be 12-18 inches apart.

4. Line the bottom of the trenches with compost – multipurpose or dedicated potato compost – if you think the soil is poor. Potatoes like slightly acid soil; if you garden on clay as we do at the Secret Garden Club, you should be fine as clay is normally slightly acid itself.

5. Lay the seed potatoes at the bottom of the trench, shoots facing uppermost, about 12 inches apart.

6. Cover with soil, adding in more compost if you think the soil needs it.

7. Try to create a slightly ridged finish to the row. This will help you remember where the potatoes have been planted!

8. In clay soil, the plants should only need watering in times of drought.

9. The potato plants should start coming through after 3-4 weeks. Once they are 3-4 inches clear of the soil you can start gently ‘earthing up’, drawing soil from between the rows to accentuate the ridge over the potato plants. You can cover the growing plants so that just the top leaves are showing through – don’t bury them completely.

10. If you find earthing up difficult, use mulch or compost to cover the plants as above. We use grass clippings a lot – the lawn always needs mowing around the time the potatoes need earthing up – which is a bit unsightly, but effective. The idea is that the developing tubers need to be in darkness, so earthing up, or covering with mulch ensures they are not exposed to the light.

11. After the potato plants have flowered, they will usually start to turn yellow and die back. This is a good sign that they are ready to harvest. Dig up a plant in a corner to check. If the tubers are tiny, re-bury them and wait a couple of weeks. If the tubers are a good size, start harvesting!

As a general rule, ‘early’ potatoes – the kind you often associate with summer and potato salads, like Charlotte, or Nicola - take around 13 weeks from planting to maturity. These can be described as first earlies, or second earlies - the latter takes about a week or so longer. Maincrop potatoes, often bakers and mashers, will be ready 15-20 weeks after planting. But note these are guidelines – and before anyone writes in, there are lots of exceptions: Pink Fir Apple is a maincrop potato which is fantastic in potato salad, Red Duke of York is an early potato that makes terrific mash. When you buy your seed potatoes, it should say on the label, or bag, what kind the variety is. The terms ‘early’, ‘second early’ and ‘maincrop’ refer to the time taken to mature: an early potato will be ready earlier than a maincrop.

Growing potatoes in a bag

And if you don’t have enough space for trenches and rows of potatoes, don’t despair. You can grow potatoes quite easily in a container, and a bin liner, a strong heavy duty bin liner like a rubble sack, will be perfect for the job. Early potatoes grow best using this bin-bag method.

1. Take a clean, heavy duty bin liner that is either black or lined black on the inside. It needs to be light-excluding.

2. Punch two rows of holes at the bottom of the bin liner with a broken pencil. These are your drainage holes, and they’re very important - the potatoes mustn't get waterlogged.

3. Roll down the sides of the bin liner to about 3-4 inches from the bottom.

4. Cover the bottom of the bin liner with a 2-3 inch layer of multipurpose compost.

5. Place three seed potatoes on the compost, space evenly, chatted shoots pointing upwards. On Sunday we planted the early variety Swift, a tasty salad-type potato which is usually quick to grow and mature.

6. Cover again with compost until no chits are showing.

7. Place the potato bin-bag outside, somewhere outside and unlikely to be disturbed by stray cats, squirrels or footballs. One of our guests on Sunday says they have a problem with squirrels and some protection might be needed here such as placing the bin-bag under mesh. Footballs is my own concern – I once came home to find my (full) potato bags being used as goalposts.

8. After 2-3 weeks you should see the green leaves appear above the compost. Let the plants grow until they have 3-4 good leaves, then add more compost to the bag so that the leaves are just showing above the surface. You may need to start rolling the sides of your bag up to accommodate the compost.

9. Keep adding compost when there is 3-4 inches of stem showing above the soil.

10. Water if the compost seems very dry. Left outside and with a couple of downpours of rain a week, your potato bags may not need watering.

11. After a couple of months, you should have rolled the sides completely up and have a bag full of compost and three healthy potato plants laying down lots of tubers. Leave the plants to flower and wait until the leaves start to go yellow and die back. You can check if your tubers are ready by sticking a (gloved) hand into the compost and feeling around for them. If they are very small, leave for a while longer.

12. If your tubers are ready to harvest, simply up-end the bag and sort through the compost for your spuds. Put the remains of the plant on the compost heap and re-use the compost – not for potatoes again, but for another crop or as a general garden mulch.