Potato Rotations and pH
by National Gardening Association Editors
Crop rotation is a must with potatoes. Troublesome insects and diseases can build up in the soil when you plant potatoes in the same spot year after year. Each season, move the potato patch to a new, sunny location. If possible, allow three seasons to pass before going back to the same area.
Since potatoes, tomatoes, peppers and eggplants are all members of the same family, consider them together. Don't put potatoes where tomatoes, peppers or eggplant were grown the previous year and vice versa.
The pH Factor
Nearly everyone who gives advice about growing potatoes mentions soil pH -- the measure of soil acidity or alkalinity -- as an important factor. Commercial, large-scale potato growers monitor their soil pH carefully and try to keep it in the range of 4.8 to 5.4, which is an acid soil condition. (7.0 on the pH scale is neutral; higher figures indicate an alkaline condition.)
The 4.8 to 5.4 pH range is important to commercial growers because the common scab fungus, Streptomyces scabies, which causes raised, scabby marks on potato skins, isn't active in soil with that pH range.
Most gardeners don't have to be that particular about the soil pH of their potato rows, though. You can raise good potatoes with a pH ranging from 6.0 to 6.5, the slightly acid condition that is still suitable for many vegetable crops. However, lower pH is better if you want greater yields and less disease.
If scab disfigures too much of your crop, you should try to reduce the soil pH. Avoid adding lime or wood ashes, which raise pH, to the soil where your potatoes will grow. While scab doesn't look great, it won't cause your potatoes to rot or decay, so you may decide to accept a little on some potatoes rather than start tinkering with your soil's pH. It's okay to eat scabby potatoes; simply peel and cook them normally.
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