Although a variety of vegetables grow best in slightly acidic or , there's a limit to the level of acidity plants can tolerate. is measured on the so-called pH scale, ranging from 1 to 14. Unlike temperature, the pH scale changes by a factor of 10 for each unit. So a pH of 6.0 is 10 times more acidic than a pH of 7.0, and a pH of 5.0 is 100 times more acidic than a pH of 7.0. Seven is neutral, and pH numbers above 7.0 indicate alkaline conditions, which are essentially the opposite of acidic.
There are no strict cutoff numbers or formal definitions for slightly acidic versus _acidic_, but as a rule of thumb, consider pH numbers between 6.0 and 7.0 as slightly acidic and those below 6.0 as acidic.
Vegetables That "Like" Slightly Acidic Soils
Slightly Acidic to Alkaline
Cabbage (Brassica oleracea 'Capitata') and beets (Beta vulgaris 'Crassa') are two vegetable crops that have a fairly broad optimal pH range, including up into the alkaline range, between 6.0 and 8.0. Peas (_Pisum sativum_) and spinach (_Spinacia oleracea_) prefer a range between 6.0 and 7.5
Lettuce (Lactuca sativa_), summer squash (_Cucurbita pepo_), winter squash (_Cucurbita maxima_), cauliflower (_Brassica oleracea 'Botrytis'), radishes (Raphanus sativas_), chives (_Allium schoenoprasum_), celery (_Apium graveolens_), broccoli (_Brassica oleracea 'Italica'), endive (_Cichorium endiva_) and carrots (_Daucus carota_) have a preferred pH range of 6.0 to 7.0.
Vegetables That Like Acidic Soils
Cucumbers (Cucumis sativus_), eggplants (_Solanum melongena_), peppers (_Capsicum annuum_), beans (_Phaseolus vulgaris_), rutabaga (_Brassica napus 'Napobrassica') and parsnips (Pastinaca sativa_) are all suited to acidic soils down to a pH of 5.5. Add to these tomatoes (_Lycopersicon esculentum_), pumpkins (_Cucurbita spp.) and sweet corn (_Zea mays_) -- suited to a pH range between 5.5 and 7.5. Potatoes (_Solanum tuberosum_) are something of a special case, with an optimal low end limit of 5.0 on the pH scale.
Test Your Soil
There's no reliable way to guess about or estimate soil pH, so having the soil tested is the best approach to ensuring that your vegetables have the proper acidity levels. The Cooperative Extension System offices in your state can help with this.