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Garlic (Allium sativum) is a hardy, perennial, bulbous herb closely allied to the onion. Unlike the onion which usually produces one large bulb, garlic bulbs are composed of several, small, elongated, egg-shaped bulbils, all of which are enclosed in a whitish skin. In propagation these bulbils or cloves are more commonly used than seeds.
Strong cloves were planted Oct. 1 at Norman, Okla., in double rows 6 inches apart. The cloves were spaced 12 inches apart and a distance of 30 inches was left between the double rows.
Early Development.--Owing to favorable weather the plants made a rapid growth and by the middle of December the tops consisted of about five leaves per plant. These were approximately 1 inch in diameter and 6 inches long. They had developed about 18 roots per plant. Most of them spread horizontally at a depth of 2.5 to 5 inches, a few grew nearly vertically downward, and the remainder took an intermediate direction of growth. They pursued a rather zigzag course through the soil, often turning sharply or forming a complete coil where a clod or other obstacle was encountered. A maximum spread of 9 inches and a depth of 11 inches were attained. Roots that did not exceed a length of 8 inches were destitute of laterals. Older and longer roots were furnished with a few branches 1 inch or less in length. These occurred on all but the youngest one-third of the roots but there were only one to two per inch. The main roots were about 1 millimeter in diameter and very tender. The characteristic alliaceous odor could be readily detected to very near the root ends.
Growth during the Winter.--On March 1, just after spring growth had begun, a further study was made. Since no freezes of sufficient severity to kill the tops had occurred, the plants grew during the winter. There were five to six well developed leaves, 6 to 8 inches long, per plant.
The number of roots varied from 25 to 50 depending upon the size and vigor of the plant. The lateral spread had been increased to a maximum of 15 inches and the depth to 22 inches. Although some of the horizontal roots still ended at about the same depth as their origin, many, after extending laterally 8 to 12 inches, turned downward 1 to 3 inches. The direction of growth of the other roots had not changed. All remained white in color and about 1 millimeter thick. Within 1 foot from the bulb, laterals were numerous. The longest ones extended 1.5 inches, often toward the soil surface. Farther from the base of the plant, they became fewer and shorter. The rapidly growing, shining, white root ends were free from laterals.
Mature Plants.--By June 12 the plants were 2 feet high and well developed clusters of sets had formed. The yellowish leaf tips and the general maturity of the plant indicated that they had nearly completed their growth. The group of bulbs at the base of the plants averaged 1.5 inches in diameter. There were now 40 to 60 roots per plant, some of which extended 18 inches laterally; others penetrated to a depth of 2.5 feet. Some of the main roots had grown to 1.5 millimeters in diameter near the plant. Laterals on these, 8 inches long near the bulb, were not infrequent. Many extended upward in such a manner that the shallowest main roots were 2 to 3 inches deep but the surface soil was thoroughly ramified. All of the laterals were longer than formerly and although not abundant on any one root, yet so many main roots ran through the soil that it was well occupied. At this time the roots did not appear to be growing vigorously. As in its earlier stages of development, the root system was very similar to that of the onion and the leek.
An isolated 2-year-old plant had an even more extensive root system which correlated with a better developed top. The latter consisted of 32 stalks. Each stalk had an average of 25 main roots, 1.5 millimeters in diameter. This thickness was maintained throughout the entire length of the white, succulent roots. A lateral spread of 22 inches, 4 inches greater than that previously found, and a depth of 40 inches were ascertained. The roots were, moreover, growing rapidly. The soil was densely filled with a network of roots. The well-developed laterals typically occurred at the rate of two per inch but not infrequently they were lacking for several inches along the root.
Summary.--The root system of garlic is very similar to that of the onion and the leek. The number, size, direction of growth, and length of the main fibrous roots are very similar, A maximum lateral spread of 18 inches and a depth of penetration of 2.5 feet are attained during the first year. The rate of occurrence of the simple laterals is also similar to that of the leek and the onion but the branches are somewhat longer than in the onion. The thorough occupancy of the surface soil was as pronounced as that in the growth of the leek and somewhat more so than that in the growth of the onion. This difference may be due to differences in soil environment.
The similarity of both roots and tops of garlic and leek to the onion explains why similar cultural practices apply to all three species of bulb crops.