Hi Allan, I am harvesting my third crop of organic spuds and busy planting the fourth, that means spring and autumn plantings over two years. To summarise my experience:
1 First planting (spring) did not have compost, but went into soil which had been under weeds for almost 6 years. They were irrigated with about 20 mm per week These sups were lovely and creamy (good for any type of eating) and had a good shelf life. However, their skins were thin and split when harvested and also during cooking. A local supermarket chain wanted them, but declined after their trial cooking tests because of the skins bursting. I never found out what the cause of that was. However, my direct customers were thrilled, with many UK Nationals saying that they hadn't had potatoes like those since their childhood in the UK. 2 Second planting (autumn) went into soil which had been heavily composted (10 cm layer of horse manure / pine shaving based compost, not the best in the world) and which had been fallow for about 2 months prior to planting (as I was not very happy with the quality of the compost). We dug 20 cm deep trenches, planted the potatoes and covered with a layer of straw mulch. This was a copy of the method employed by a friend. The idea was to shovel the soil back into the trenches as the spuds grew. That never happened for various reasons, and so the sups landed up growing in subsoil, without the benefit of the compost, other that what had leached into the profile. Those spuds were not as good as the first planting, but better than conventional. 3 Third planting was into soil which was heavily composted about 12 months before, and had produced a wonderful winter crop of cabbage, cauliflower, broccoli, spinach and beetroot, the soil having been turned after these crops were harvested. These potatoes have been good eating (roasting better than boiling and baking), but still not the same quality as the very first planting. 4 I have in the meantime planted about 50 comfrey plants, for use in my current planting. The procedure has been somewhat different than before, due to a shortage of labour and managerial time. The field has been fallow and under weeds for 4 months, but has been regularly mowed, thereby acting as a green manure / in situ mulch. Small holes have been dug for each seed potato. However, a comfrey leaf and handful of compost (my compost volumes have dropped dramatically, as I had spent a year collecting stable bedding and manure before the second planting) are placed in the hole, the seed potato on top and then covered with soil. These spuds are only just starting to show their first leaves, so I don't know what they will be like. The theory is that the comfrey gives them the calcium they need in otherwise calcium poor soil. Some notes: 5. The third planting was into soil with a pH 5,5 - 6 (water), which is considered ideal for summer rainfall areas in South Africa. However, the lands are infested with nutsedge (Cyperus esculentus, Kyllinga alba and K. erecta) as well as False garlic (Nothoscordum gracile) and some of the potatoes had scab (Streptomyces scabies). I read somewhere (can't find the reference now) that the weeds indicate an acidic pH, the scab an alkaline pH, yet the pH readings were supposedly OK! I have not resolved this one, unless the pH (KCl) should be 5,5 - 6. Even then, I don't know what the answer would be. 6 Some of the potatoes have bumps, called marbles, on them. This just disfigures the potato, but does not affect the taste. Unconfirmed diagnosis is that this is because of one of the nematodes. 7 My soils are sandy (<20 % clay). 8 Some of the first planting had gem squash and marrows as companion plants (adjacent marrows and squash grew into the potato field). Surprisingly, those marrows and squash which grew with the potatoes were NOT stung, while those adjacent to the potatoes were! 9 Hollow heart was a problem in the first planting, due to soil deficiency in Mo. I foliar fed (two sprayings) subsequent plantings with Mo and B which seems have had the desired effect. I think that three sprayings are needed though. 10 Finally, spraying with Effective Micro-organisms (Kyusei Nature Farming), has helped with early blight and delayed late blight. The late blight now comes when the plants start dying off in any case, which I believe is a natural consequence of senescence. Seaweed extract foliar feeding has also been worthwhile. I have not had much success in finding out about organic potato production. So I hope that this helps. Best wishes Stephen Barrow
