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Parsley (Petroselinum hortense) is a popular garden herb belonging to the carrot family. It is a biennial or perennial plant grown for its leaves, which are used for garnishing, flavoring, and sometimes for salads. Only the foliage of the first year is used. The second year the plants produce stout flower stalks, 1 to 3 feet tall. The plant develops slowly and is not ready for use until rather late in the summer.
Parsley of the Champion Moss Curled variety (P. hortense crispum) was planted Apr., 27 in drills 1 foot apart. After germination and establishment the plants were thinned to 4 inches apart in the row.
Early Development.--By June 23, when the first examination was made, the shoots were over 2 inches tall and had a spread of about 1.5 inches. Plants of average size had 5 leaves. The small transpiring area of the much-dissected leaf surface was reflected in the rather poorly developed root system. This consisted of a taproot and its branches. Although 2 to 3 millimeters thick near the ground line, the main root tapered rapidly to a thread-like structure only about 0.5 millimeter or less in diameter. Several taproots were traced to depths of 16 to 18 inches , the last 3 to 4 inches always being unbranched. Practically no branches occurred on the first inch of root. Between 2 and 8 inches, however, they averaged 9 per inch, varying from 3 to 16 in number. Nearly all were horizontal, from 0.1 to 6 inches long, and many were unbranched. Others were furnished with short branches only 0.2 to 0.5 inch long at the rate of 2 to 4 per inch. At greater depths branching was even poorer and the laterals shorter and simpler (Fig. 64). The roots were glistening white, fine, and delicate.
Fig. 64.--Showing root habit of Champion Moss Curled parsley about 2 months old.
Midsummer Growth.--A second examination was made Aug. 5. The plants averaged 4 inches in height, had a 9-inch spread of tops, and those of average size were furnished with 22 leaves. The taproots had now reached a diameter of 0.5 inch near the soil surface but tapered to 2 millimeters in thickness at the 1-foot level. At 2 feet they were usually only 0.5 to 1 millimeter thick. These thread-like roots pursued their tortuous course to maximum depths of 44 to 50 inches. The last 8 inches were usually free from branches.
At a depth of 2 to 12 inches 60 branches took their origin, sometimes 9 laterals arising from a single inch of taproot. These were mostly only 4 to 6 inches long although 18 to 20 of the lot were 1 to 1.5 millimeters thick and reached lengths of 2 to 3 feet. In general their course was at first outward and then obliquely downward, the lateral spread seldom exceeding 18 inches. Rebranching occurred at the rate of 3 to 8 laterals per inch. They were usually 0.2 to 2 inches long, and rebranched with short laterals at the rate of 3 to 5 per inch.
Between 18 inches and 3 feet in depth horizontal laterals arose at the rate of 2 to 6 per inch. They varied from 0.2 to 10 inches in length, 2 inches being an average. The longer ones were rebranched. Below 3 feet branching was poorer (one to two branches per inch) and the laterals were short (average 0.1 inch) and simple. The rate of branching, especially in the first foot, was always much greater on the distal ends of the laterals. For example, the proximal half of the larger laterals usually had about six 0.2-inch laterals per inch; the distal half averaged 9 branches which varied in length from 0.2 to 3 inches. In fact this difference in branching habit was very pronounced. Many of the smaller laterals were dead and dry.
The effect of soil structure and perhaps increased aeration were strikingly shown at the 24- to 30-inch level where the roots of some of the plants passed through the loose soil of a filled rodent burrow. Here the rate of branching was distinctly greater, the branches much longer, and all were much more profusely rebranched.
Compared to other crops, parsley has a rather meager root system, a fact undoubtedly correlated with its smaller transpiring area.
Summary.--Parsley is characterized by a taproot system with major branches originating only in the surface foot of soil. The branches at first spread outward but soon turn downward so that the roots are confined within a radius of about 18 inches from the base of the plant. Many attain depths of 2 to 3 feet . The rather delicate taproot penetrates to the 4-foot level. Like the main laterals, it is fairly well furnished with branches but these are mostly short although often well rebranched. As a whole the root system grows slowly and does not ramify the soil so completely as do many other vegetable crops. It should be stated, however, that the plants studied had not completed growth.
Parsley of the Extra Double Curled variety was grown at Norman, Okla., in rows 3 feet distant. The plants were spaced 1 foot apart in the rows. The early growth and root development were so similar in every respect to that of the parsley at Lincoln that they require no separate discussion.
Growth of both tops and roots practically ceased from the middle of July until the middle of September. This resulted from the hot, dry weather. Within a few days after the autumn rains, about the middle of September, growth was resumed. As regards the roots, growth consisted of a renewal of laterals on the taproot and main branches as well as a renewal of growth at the tips of the roots already formed. The tops responded quickly to the increased absorption and by Oct. 1 leaf development was pronounced. This growth continued for a period of about 2 months and the tops increased in total spread from 7 to 13 inches, the leaves lying flat on the soil surface. After Dec. 15 growth was intermittent and although the plants were very hardy there was not much change in tops or roots until Mar. 15.
Resumed growth was initiated by the appearance of a few new rootlets from the taproot and its larger branches. But for the most part root development consisted of rebranching and extension of the roots already present. Above ground, erect leafy branches began to appear. By June 10 they had attained a height of 2 feet. The branching flower stalks were abundantly clothed with flowers and fruits.
By this time the taproot had increased to 1 inch in diameter. The 12 to 18 main branches from the first 8 inches of the taproot were 2 to 4 millimeters thick. Although many of the roots turned downward within 6 to 8 inches of the plant, a lateral spread of 42 inches was observed. The maximum penetration was 56 inches.
Root growth during the second season consisted almost entirely of renewed branching and growth of laterals rather than an extension of the older major roots into new soil. Thus the soil volume occupied by a plant was but little, if at all, increased, but the degree of ramification was much greater.
Other Investigations on Parsley.--Roots of parsley have been washed from a clay loam soil underlaid with a tenacious clay subsoil at Geneva, N.. Y.
In this plant the root system was found to be extensive, and especially deep. On Sept. 17 the roots of a plant of the Common Curled and one of the Hamburg or turnip-rooted variety were washed out. Little difference appeared in the roots of the two sorts. In each the taproot was traced to a depth of 2.5 feet without coming to the end. At this depth the horizontal branches were frequent, being little if any more than ½ inch apart. At a depth of 18 inches the soil was pretty well filled with fibrous roots. The branches usually left the taproot in a horizontal direction and not infrequently grew slightly upward. At a depth of 4 inches below the surface a horizontal root was traced a distance of 2.5 feet. Many fibrous branches came to the surface. 44
Root Habit in Relation to Cultural Practice.--The position of the upper portion of the root system so near the soil surface shows clearly that it would be greatly injured by any but shallow cultivation. The slow growth both aboveground and underground makes it a poor competitor with weeds, hence the practice of clean, shallow cultivation throughout the growing season. The closer spacing of parsley plants (usually 4 to 8 inches apart in rows 15 inches distant) than in many other garden crops is quite in accord with its smaller root system and less extensive tops.