The arrival of some ulluco (Ulluco tuberosus) tubers from Incredible Vegetables left me pondering how best to store them until it’s time to plant them out (after the risk of frost has passed, in spring). Given that I also have mashua and oca tubers kicking around the kitchen, and that everyone will soon be receiving seed potatoes (if they haven’t already), then I thought it might be nice to have a general round-up of how to store tubers for planting. A lot of the advice will be relevant to all kinds of tubers, but each species is likely to have its own quirks. If you have advice, details for new species, or queries, then leave them in the comments – I can update this post later.
How to store ulluco tubers
In their advice on how to grow ulluco, Incredible Vegetables recommend keeping your seed tubers in trays of slightly damp compost in a frost free dark place until March (early spring). Nearer to planting time you can bring them out into the light and they will grow sprouts and leaves (a bit like chitting potatoes, see below) and they can be carefully transplanted into pots to grow on, or outside when the risk of frost has passed.
In their how to grow ulluco guide, Cultivariable note that ulluco tubers store very well in cool conditions, although they can dehydrate in dry air. However, they say that even badly dessicated ulluco tubers usually survive if potted into damp soil. Their recommended treatment for tubers that are going soft, is either to put them in some moist soil or in the fridge.
How to store seed potatoes
In their potato guide, the RHS recommend that potatoes are dug on a dry day if they are to be stored, and that the tubers are left on top of the soil for a couple of hours for the skins to ‘set’ and harden a little. Gentle handling is required to avoid damage – damage tubers won’t store and should be eaten. They are best stored in hessian or paper sacks or in boxes in a frost-proof shed, and early and second early potatoes have a short dormant period and keep for a shorter time than main crop cultivars.
Sárpo potato varieties are a little bit different – they have extended dormancy, and dried tubers can be stored in a frost-free shed without refrigeration until spring or even early summer.
They benefit from chitting to kick start them into growing in the spring, and I think the general consensus these days is that chitting is helpful for all potatoes. If you have seed potatoes waiting to be planted, chitting them on the windowsill, where they will grow green, stubby sprouts in the light, is the easiest way to store them for a few weeks.
How to store oca tubers
Oca (Oxalis tuberosa) is known by various names, including the New Zealand yam. Real Seeds offer a simple storage method – recommending that you store the tubers in a paper bag or envelope in a cool but frost-free place. They note that the garden shed isn’t the best choice for storing tubers, or indeed any seeds, because of the temperature fluctuations.
They also mention that stored oca tubers may start to sprout any time from January (mid winter) onwards, so you need to keep checking. In the absence of light they will form long, tangled sprouts (like potatoes). If yours are starting to sprout then pop them on the windowsill to chit, just like potatoes, to encourage the growth of short, fat sprouts.
If you’ve grown oca before and want to save some tubers for replanting, Thompson & Morgan suggest lifting them carefully, drying them and storing in slatted trays or a hessian sack in a cool shed or garage. Take care not to bruise or damage them, as this can encourage them to rot.
I know from experience that oca tubers can dry out and start to wrinkle, and that it’s not necessarily a death sentence – they’re robust things. If you spot some past their best then try potting them up in damp compost and seeing what happens. In all likelihood they will recover and start to grow.
How to store Jerusalem artichoke tubers
Jerusalem artichoke (sunchoke) tubers store best in the ground. If you’re storing them to eat then they will keep in the fridge or root cellar for a couple of months (according to Mother Earth News. If your soil freezes solid over winter then consider building a clamp to keep them cool and moist but accessible.
If your soil isn’t frozen solid then just go ahead and plant your Jerusalem artichokes – they will survive whatever the weather can throw at them. Or pot them up and (if need be) transplant them later in the year. They’re pretty indestructible.
Thompson & Morgan have a guide to growing sweet potatoes in the UK, which still isn’t the easiest thing to do (although better varieties are appearing every year). They say that sweet potatoes store well for several months if the skins are cured properly, which involves laying your harvest out in the sun for a few hours. Tubers are then moved to a warm, humid place for 10 days – a greenhouse is ideal. Once the skins have cured the tubers can be stored in cooler, dry conditions.
I’ve done this once myself, and when the sweet potato started to sprout in spring I potted it up in moist soil, and kept it indoors. Later I potted the shoots it produced – when rooted these are called ‘slips’ and it’s normal to buy sweet potatoes as slips for planting, rather than seed tubers. In fact, these days, most of the seed companies are selling plants ready for planting out (when the weather is warm enough), so tuber storage isn’t much of an issue here.
According to The Lost Crops of the Incas, mashua tubers have a high moisture content and lack a waxy surface, which means they don’t store as well as some other tubers. However, it notes that they can be stored for up to six months in cool (frost-free), well-ventilated conditions, out of strong sunlight.
In their guide to growing mashua, Cultivariable also note that mashua tubers are particularly vulnerable to dehydration, and suggest that they do better stored in soil. (Tubers will last six to eight weeks at room temperature and moderate humidity before they become unappetizing to eat.)
By early spring those mashua tubers will be sprouting, and then they need to be in the light so that they grow nice sturdy sprouts – you can pot them up and transplant them later, they don’t mind being disturbed.
Lots and lots of gardeners save dahlia crowns for replanting the following year – the RHS includes advice on how to do that in their dahlia section. It’s aimed at ornamental growers, but the principle is the same for those intending to eat their dahlias.
I’m still learning how to do this. So far I think that the eating tubers store best when still attached to the crown of the plant, kept in trays of slightly damp soil in frost-free conditions. Mould is potentially an issue, so keep checking your stores. I haven’t tried keeping any tubers in the fridge yet, but I know that they start to soften and dehydrate if left on the kitchen counter.
However, Mat Coward suggests storing dahlia yams like root crops – he says they will keep for months if they are separated from the root cluster and buried in a box of sand in a cool (frost-free) place.
Tubers are then planted out in late spring or early summer, once the risk of frost has passed.
So… how do you store your tubers for planting? Do you have advice to add, or questions? Is there a tuber species you’d like to see added to this list?
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