The grouping of vegetables gives the student a better understanding of the character, requirements and uses of the various crops. The arrangement based solely upon botanical relationship is the most exact system, but in many cases is of little advantage in helping to determine the best cultural conditions for each crop. The uses of the plants also constitute an important basis for classification. All vegetables may be placed in two general groups in respect to their hardiness, viz., (1) "tender" plants, or those which are injured or killed by frost, and which require high temperatures for successful growth, as tomato, pepper, eggplant, bean, melons, squash, cucumber, sweet corn and sweet potato; (2) "hardy" plants, or those which are not injured by frost, many of them in fact bearing severe freezing and thriving at temperatures too low for "tender" plants. The "hardy" crops include pea, cabbage, kale, spinach, asparagus, rhubarb, celery, lettuce, cress, radish and many other plants. The line, however, between "tender" and "hardy" plants is largely arbitrary. Celery, for example, is properly classed with hardy plants, while comparatively light frost or low temperatures may check the growth of young plants and cause them to produce seed shoots. The onion is also regarded as a hardy plant, while seedlings of certain varieties are injured by light frosts.
The best system of classification has been devised by Prof. L. H. Bailey ("The Principles of Vegetable Gardening," pp. 240-242), and is followed in this chapter. It is based primarily upon methods of culture, although other factors are considered. The system provides for two general classes; namely, annual vegetables and perennial vegetables. These classes are then divided in subclasses according to the uses of the crops, and each subclass is composed of groups, determined mainly by their cultural requirements. The scheme of classification proposed by Professor Bailey is as follows:
Beet (Beta vulgaris). Carrot (Daucus carota). Celeriac (Apium graveolens). Chicory (Cichorium intybus). Horse-radish* (Cochlearia armoracia). Parsnip (Pastinaca sativa). Radish (Raphanus sativus). Salsify (Tragopogon porrifolius). Turnip and Rutabaga (Brassica).
Sweet potato (Ipomoea batatas).
Kale (B. oleracea).
Kohl-rabi (B. oleracea).
* Horse-radish and dandelion are perennials but usually occupy the ground only one year.
Beet (Beta vulgaris).
Chard (B. vulgaris).
Dandelion (Taraxacum officinale).
Mustard (Brassica species,).
Sea kale (Crambe maritima). Spinach (spinacea oleracea).
Celery (Apium graveolens).
Corn salad (Valerianella olitoria).
Bean (Phaseolus, Dolochos, Vicia).
Pea (Pisum sativum).
Eggplant (Solatium melongena).
Pepper (Capsicum annuum). Tomato (Lycopersicum esculentum).
Tomato, husk or strawberry (Physalis).
Cucumber (Cucumis sativus).
Gherkin (C. auguria).
Muskmelon (C. melo).
Watermelon (Citrullus vulgaris).
Martynia (Martynia proboscidia).
Okra (Hibiscus esculentus).
Sweet corn (Zea mays).
Not discussed in this book. It is more generally regarded as a forcing crop.
Artichoke, globe (Cynara scolymus). Artichoke, Jerusalem (Helianthus tuberosus). Asparagus (Asparagus officinalis). Rhubarb (Rheum rhaponticum).
Sea kale (Crambe maritima).
Root crops (Group 1) thrive at comparatively low temperatures. They usually prefer sandy loams, and deep soils are also important for long-rooted crops. Sandy types of soil favor symmetrical development of roots and decrease the percentage of the small, fibrous roots objectionable in this class of vegetables.
The sweet potato requires a long season and high temperatures. Sandy soils are preferred.
Bulb Crops (Group 3) are hardy and may be grown successfully in many soil types, although sandy loams are best. They do not require high temperatures, but the soil must be well provided with humus and available plant food.
Cole Crops (Group 4) are hardy and require a cool season, a fertile soil and an abundant supply of moisture.
The requirements of the "greens" (Group 5) are variable. (See Chapter XXI).
Salad Crops (Group 6) are hardy. They require liberal feeding and an abundance of moisture.
(Group 7) Soil and weather requirements vary with each crop.
Solanaceous Crops (Group 8) are "tender" vegetables that must not be planted in the open until there is no danger of frost.
Cucurbitous Or Vine Crops (Group 9) are "tender" vegetables that require high temperatures and usually a long season, Sandy loams preferred.
(Group 10.) High temperatures are necessary for the best results. The soil should be moist and fertile.
The soil should be enriched annually by the application of rotten manure. Nitrogenous fertilizers are especially beneficial.
Although the foregoing method of classification is exceedingly valuable, the requirements of crops, even in the same group, are so variable that a complete discussion of each crop is necessary to give accurate cultural directions. The vegetables are taken up in alphabetical order, because this arrangement makes the book most convenient for reference.