Although the garden centres start to sell their seed potatoes in early January, mid March is a suitable time to think about a first planting outdoors. I keep my seed potatoes in the refrigerator, where they can store successfully until the autumn. Three or four weeks before planting they are placed to chit, rose end up, in egg boxes. I have sometimes seen it suggested that they be chitted in a dark place, but this is, in my view, incorrect. They should be placed somewhere light but not overly warm. The dark results in the production of spindly pale shoots that are rather weak, whilst in the light, they form short, strong, shoots ready to grow away well. Traditionally, earlies would be planted first, followed by second earlies, then late sorts, over a period from about mid March to late April. The planting of main crop potatoes was often undertaken around Easter.
Our first potato planting was made in large pots in the glasshouses at the start of February. Some six weeks later, these are developing very well, with foliage well over the top of the pots. The pots were half filled with a rich compost mix when planted, so last week we topped them up with a mixture of homemade compost and a little peat free multipurpose. This job is easiest with someone to help hold the foliage out of the way whilst compost is shovelled into the pot. Fortunately, Dad was on hand to assist. Growing under the protection of the glasshouses, with their south facing rear walls, generally prevents any frost damage. If a cold snap is forecast, I tend to top up the compost to cover the shoots. This year, though, it has not been necessary due to the mild weather. Additional protection could always be provided with some fleece. Our first crop should be ready after another six weeks or so.
For the outdoor sowing, we used a rake to prepare two deep furrows along the length of one of the 4’ wide beds. Later, as the shoots start to develop, these furrows will be filled in and then soil ridged up around the potato plants. This helps to exclude light, which turns the tubers green and inedible, as well as providing a good depth of soil. I tend to plant at much closer spacings than would normally be recommended. I must confess that I have not undertaken any serious trials relating to planting distances, so all I can say is that I do seem to achieve good yields of good sized tubers despite the close planting. I have read some research that might support closer spacings. Two factors that may help are a rich soil and deep planting, which gives a good vertical space. Deep planting is also beneficial in dry conditions, as the deeper soil remains moist for longer. The size of the seed tubers influences the number of stems, which in turn affects the number of tubers and their size. Smaller tubers can be planted more closely. A higher density tends to produce more tubers, up to a point, but generally smaller, although we get good sizes from our second earlies and main crops. In any event, I usually have a surplus of seed potatoes so am quite happy to plant more densely.
The bed was prepared in the autumn with the addition of a good layer of horse manure. It was then covered over the winter with weed suppressing membrane. When we uncovered the bed it was found to be in excellent condition, the worms and other soil organisms having done their job in processing the compost and leaving a reasonably light soil, despite the heavy rains. The potatoes are laid out along the base of the furrows, allowing a little more space for the main crop varieties than the earlies. We then use a towel to plant the tubers fairly deep along this furrow. It makes harvesting hard work, but the crop seems to be good. Planting at this time of year, one might, here in the south, avoid frost damage to the shoots. However, as they emerge after a few weeks, the furrows can be filled in, bit by bit, to cover and protect the growing tips.
In this bed we sowed first early Epicure, second early International Kidney, and main crops Arran Victory and Golden Wonder. The next batch has been put out to chit, comprising more International Kidney, the general purpose second early or early main crop Wilja, and the late main crop Pink Fir Apple.