The potato is one of our most important kitchen garden crops. It’s the mainstay of home production; from new potatoes loved by everyone to the long-storers keeping us through the lean months. Unknown before the Americas were discovered it was not the most rapid success when first introduced and many other alternatives were tried before the spud triumphed.
There was a big need for winter storing crops. Cabbages, carrots, huge turnip like roots and parsnips were not enough. Sweet potatoes were amongst the first New World crops experimented with, but proved too difficult to over-winter, the tubers can’t be stored like potatoes and slips need to be rooted in autumn and protected throughout winter. Jerusalem artichokes were also introduced, several times, and always failed to please, that is despite being productive on poor soils! Believe it or not the Dahlia was even originally introduced as a potential root crop – and failed to please even more than Jerusalem artichokes. The spud won.
Once a plant of the foothills of mountains the potato evolved both spherical seed capsules and spheroidal tubers. Either could roll and lodge in cracks after soil disturbance. They could start new plants from seed, or from the tubers which sprouted new shoots and roots easily from their stored starch. The tubers are actually bits of swollen stem and grow on the ends of side shoots not on the roots proper. That’s why they go green (and poisonous) if they are exposed to light for long. Thus any tuber, or even a bit of one with an eye, or bud, can produce a whole new plant just like it’s parent. They can be grown from see, like tomatoes but take too long to produce a decent crop that way. Conventionally we plant egg sized tubers, sets or seed potatoes in spring, but there are other ways of treating them.
The Victorians preferred saving bigger tubers. Bigger tubers for ‘seed’ give by far the best performance in my experience. Egg sized is the most economical-return size favoured by farmers but larger is better for the home gardener. Even smaller than egg sized tubers can be used, but are easily lost in a frost, and may not do very well especially if selected by default from the entire harvest. (It’s too easy to inadvertently grow a strain that tends to produce lots of small tubers; an accident awaiting anyone who selects from a mixed up harvest. Only ever save your own sets from healthy well yielding plants, ideally the biggest tubers! If you plant the small ones left after lunch has gone then you may soon breed a mini-potato.)
Any plant to be worth growing needs to be grown from big tubers or your yields will probably drop in a year or two. The Victorians compromised by chopping the biggest seed tubers in three. They preferred the rose end, used also the middle slice but discarded if possible the haulm end part where it had been attached to the plant. They believed this part gave late growth and thus light crops. Indeed to this day we know we should stand seed potatoes in egg trays on end with the rose end up. This, the ‘stems tip’ ends with lots of eyes, buds, in a spiral for the ‘rose’ of the name. It’s these buds which break easiest and make the quickest growth and heavier crops. I found this so with yields greatly reduced when some of my sets were deliberately chitted or planted the wrong way up.
Now there seems to be an innate slowness for eyes to sprout at the haulm end because when chitted upside down the shoots from the rose end grew first in many cases and bent round to grow up and past the slower haulm end. A little more care could give much bigger yields if you have been sloppy about setting out the seed potatoes properly.
Now for new potatoes you want lots of tubers quickly, so you leave all the eyes on the sets to make lots of main shoots, many side-shoots and so get lots of small tubers early. But for storing crops, for bakers and chippers; bigger tubers are more desirable. Now this is a function of picking good sets, preferably large of a large growing sort, and giving them good conditions and wide spacing -and reducing the number of tubers per plant so each grows bigger. This can be brought about by rubbing off all of the sprouting eyes bar three, on the rose end, when planting. Thus the plants are reduced to three main shoots fewer side-shoots and bigger tubers. If everything else is ok.
Bigger crops obviously come from rich well balanced moist soil in a sunny place. Shade makes for less crop and drawn up tall haulm. Dry conditions gives harder smaller tubers that keep well and often have little slug damage. Huge increases in yield come from good watering though, a doubling of yields compared to the ten or fifteen per cent gain got from a good digging. Though digging does help, do as much as can be done and as you want, it all adds to the crop a tad. Fertiliser, preferably organic increases the crop, as does foliar feeding with seaweed sprays. But more effective is adding organic matter, be it farmyard manure, compost, grass clippings or dug in green manures before planting. Surprisingly nipping the flowers off before the seed pods have set can increase yields by almost as much as all that digging!
Planting early is good as the total weight of crop is increased by the length of the growing period- so main crops have to be growing on into early autumn before you dig them. Ear;ies are designed to crop quickly so always give lighter crops. Chit Earlies by standing them rose end up in a warm light place to start them into growth even earlier so the harvest comes sooner still, but is lighter because of the shortness. It is worth it for Earlies but chitting is wasted on Main crops who then crop lighter too, but earlier which may help them miss a late blight.
Another way, other than cloches etc, to get bigger crops is to start the main crops off in pots under cover and plant these out after hardening them off. And any good shoots rubbed off big tubers need not be wasted as they can be potted up and given a tad of bottom heat soon turned into small plants to be potted on and treated as tomato plants until planted out after the worst frosts. If well grown well till then in large pots and hardened off these can give very good crops. You can multiply one sported tuber into a half dozen plants or more this way with much more crop. (If you force a tuber to produce sprouts the first flush are normally true to the parent plant. However if you continue to force new shoots some varieties revert and produce older precursors so Golden Wonder can be made to recreate it’s ancestor Langworthy and Field Marshal produces Up to Date. Similar happens if you excise the eyes and force the tuber.)
It is relatively easy to root bits of potato stem or get eyes or small sprouts to make small plants in autumn but then not at all easy to over-winter these. The Russians even famously used potato peelings to start off plants- it works well as long as it has an eye and does not rot. As with cutting up sets the problem of rot for a peeling is great but so is dessication. The good practice has been to dip the cut surfaces in wood ashes to help stop them rotting or just to air dry them. But in fact they need to be wet longer to heal well but then they may rot, you can’t win…
The traditional ridge method gives a warm seed bed and the earthing up with a soil mulch to prevent the tubers greening also helps control weeds but neither is essential. On the flat the crop may be a tad later or brought up to speed with plastic sheet mulch warming the soil before planting. And the earthing up, it’s done to support and encourage the haulm to root, to cover it from frost and to later cover the tubers. But it does not have to be soil dragged up about the plants, it can be leaves, newspapers, cardboard or even grass clippings. I prefer grass clippings as put on in successive thin layers they work well and enrich the soil. (Dug in before planting grass clippings also reduce scab attacks, those rough patches on the spuds skin)
I also use straw when I can get it as it makes excellent mulch. It suppresses weeds but does not form a ‘skin’ and potato haulm can push up through it. This makes it perfect for autumn planted potatoes. These are put in when the soil is cooling and then covered with thick straw. (Bracken can apparently be used or leaves) Nothing is done till harvest as there is no weeding, feeding or earthing up. Some sets occasionally fail through rats, really wet or really cold winters but otherwise it’s a good method as they do at least as well as volunteers. (The plants that come from spuds missed when harvesting- which annoyingly do so well)
Some have grown potatoes through black plastic sheets which acted as earthing up and weed control- but the slug, and vole or rat damage was too severe in my trial.
Earthing up is good for covering the tubers stopping them greening but with main crops it may also encourage more side-shoots and a bigger crop. This has been exploited by the barrel or car tyre method. A seed of an old main crop variety (modern ones sometimes have short haulms and do not respond) is planted in compost in the bottom of a drum, barrel or a big car tyre early in the year. As the haulm emerges it’s protected against frost with a cloche, once it’s a foot or so tall the container is filled till the haulm is just showing. With tyres another one or two are added to the stack and filled. Then when another foot or so of haulm is grown up this too is earthed up, and then again. Three or so earthing ups with plenty of watering, and feeding, have enabled some to achieve unbelievable yields from just one plant. (Earlies die too quickly to work by this method)
Potatoes can be grown in containers anyway as long as they are always well fed and watered. They’re easier in the soil, but for extra early crops it’s really worth planting sets of early varieties in big pots from Christmas and New year on as long as you have a light frost free place to keep them. They will give small crops by Easter when everyone else is just planting theirs! One warning though- although you can grow potatoes indoors in a frost free light place if it warms up too much they grow all tops and no bottoms, ie they do not crop well if too warm! The same can happen in sheltered gardens in good summers. And if you want new potatoes for Christmas keep sets in the fridge instead of planting them in spring and plant them in big pots in late summer, under cool cover. Don’t dig the crop till you want it. Or- when you dig your best new potatoes bury some deep packed in damp sterile compost in a tin in a cool shady spot.
A cause of really tiny crops, or no potatoes, is if the sets were put into really chilly soil after being chitted in the warm. They can go into shock and just produce small offsets- these are sometimes found in old bags of surplus potatoes left to waste. Indeed you can recover some good from sprouted wilted spuds by packing them in clean compost in the dark; they make little new ones for almost free.
Another way to get a tad more for nought is when you dig your crop of earlies, or indeed of any if the haulm is still green. Treat it carefully and do not detach the tiny tubers still left. Replant the haulms and roots at the end of the row or in a tub in good soil or compost and keep this well watered. ~Although they will wilt and shrivel away they will fatten the tiny tubers with the last of their strength and give you a small bonus.
When you dig any crop always set aside the best cropping healthy plants tubers for sets. Use any damaged or small spuds first saving the best for storing. Ideally dig on a sunny drying day and leave the tubers in the sun for an hour or two before packing them away in paper sacks or trays in a cool dark place. I use dead freezer units as they stay at a constant temperature in a shady shed and are rodent proof! Be warned- If stored tubers are lightly frosted they become sweet and not palatable, badly frosted and they rot. Also they can pick up taints from smelly things around them.
If you have blight (black patches on leaves and stems, smells awful, stems fall and rot down) then cut the haulm off before the blight runs down to the tubers. Although you have a lighter crop as they finish too soon you can save it from the blight if the haulm is cut off in time. The crop must be left a fortnight before lifting. If you do get blight and leave the haulm to die the rot runs down and the tubers go browny red under the skin and rot. Apparently though they remain edible; a mad Frenchman survived on boiled blighted potatoes for more than a month. Now there’s something to look forward to trying….