Very few garden crops can be fertilized as heavily as asparagus and a profit be made on every dollar expended for plant food. Many of the most successful growers believe that the largest net returns cannot be realized without an annual investment for plant food of $60 to $80 an acre. Stable manures have been practically abandoned by some growers, but the safer practice is to apply them liberally enough to maintain the supply of humus. From one to three tons of commercial fertilizer an acre may be employed advantageously on established beds.
There has been much discussion as to the character of the fertilizer adapted to this crop. According to analyses made by Wolff, a ton of fresh sprouts contains 6.4 pounds of nitrogen, 1.8 pounds of phosphoric acid and 2.4 pounds of potash. The best fields produce at the rate of three tons an acre, and this would require 19.2 pounds of nitrogen, 5.4 pounds of phosphoric acid and 7.2 pounds of potash. It is very evident that the shoots themselves do not abstract large amounts of plant food. To meet these needs it would take only 128 pounds of nitrate of soda, 38 pounds of 14 per cent rock phosphate and 14 pounds of muriate of potash. Now, why do expert growers feed their plants with such great liberality? Because other factors besides the mere production of shoots must be taken into account. The enormous root system and the tons of tops renewed every year must be supported. Again, growth of both shoots and tops must be very rapid, and consequently there must be no shortage in the supply of quickly available plant food.
Nearly all growers agree that nitrogen is the most important element of plant food for asparagus, and while the majority of them believe that it should be applied in the form of nitrate of soda, some growers prefer organic material, as dried blood, tankage, fish scrap or cottonseed meal. As to the best commercial fertilizer to use, investigators and practical growers differ widely in their recommendations. Voorhees suggests the basic fertilizer, 4-8-10, supplementing with heavy applications of nitrate. Rolfs recommends 4-5-7. An expert New Jersey grower uses a 6-7-5 formula. Many practical growers prefer 5 or 6 per cent of nitrogen.
The proper time of application is a much disputed question. As the leaves or elaborating organs are not permitted to develop until after the cutting season, it is argued by some that the proper time to apply nearly all of the plant food, both stable manure and commercial fertilizer, is after the cutting season, when the leaves are formed. Voorhees and others believe that the plants are benefited by early spring applications, especially if green shoots are produced. On the other hand, we must not lose sight of the fact that next year's crop is mainly dependent upon this year's top and root development. Large tops and strong roots mean heavy shoots next year.
If seeds and plants have been selected intelligently and all cultural conditions are favorable, the following treatment should give excellent results: Apply 10 to 15 tons of fine manure early in the spring, or probably with as much benefit immediately after the cutting season; one and one-half tons of a 4-8-10 mixture, half applied in early spring and half immediately after the last cutting; 150 pounds of nitrate of soda by broadcasting as soon as growth begins in the spring; 150 pounds of nitrate of soda when the cutting season is half over; 150 pounds of nitrate of soda at the close of the cutting season and the same quantity one month later.
Common salt was used in large amounts on asparagus beds until quite recently. It possesses no fertilizing value, and although it draws some moisture and is injurious to weeds, its use is no longer considered an advantage by successful commercial growers.
When the most intensive methods are followed, the rows are made closer together than when the crop is grown on a large scale. It is held by many growers that close planting necessarily results in smaller shoots, but this is not the case with skillful intensive gardeners. More space between rows is obviously required when high ridging is necessary to grow the white shoots, although French producers of white spears plant as closely as most American growers of green shoots. Wide planting is also favorable to convenient cultivating, and plants and roots will not begin to crowd so soon. Therefore the plantation should be profitable during a longer period of years. On the other hand, wide planting materially limits returns for several years, and for this reason there is some tendency to plant closer and make new beds more frequently.
Planting distances vary considerably in different sections. In the growing of white stalks, the average spacing in England is probably 16 inches by 4 feet; in France, 2×4 feet; in Germany, 3« × 4 feet; in the largest fields in California, 2 × 9 or 10 feet (on reclaimed land); in New Jersey, 2 × 5« feet; in New York, about 2×5 feet. In New Jersey green asparagus is usually grown 2 or 2« × 5 feet; at Concord, Mass., 2×4 feet; in Pennsylvania, 2 × 4 or 4« feet. An extensive grower in Philadelphia County, Pa., plants 4×4 feet, while an intensive grower at Cleveland, O., plants 1×3 feet. Peter Henderson recommended 9 inches by 3 feet.
Fall planting is occasionally practiced, but spring planting is universally regarded better. After the ground has been plowed and thoroughly harrowed, deep furrows must be made preparatory to setting roots or crowns. If the land is steep enough to wash, the furrows should run at right angles to the direction of the slope; if practically level, north and south will insure the most even and perfect distribution of light on all parts of the row. The depth of the furrow should be determined mainly by the natural depth of the soil. In America the crowns are set 6 inches to 1 foot deep, but 8 inches is considered deep enough, although 10 inches may be an advantage. Certainly, the crown should never be set in the subsoil, where the fleshy horizontal roots would fail to find food or proper physical conditions. Deep planting is regarded as important in the production of large shoots, but the chief advantage is to get the crowns beyond the reach of tillage implements. As the new buds form higher on the crown each year, deep planting, therefore, prolongs the time when there will be any interference by tillage tools. The first shoots will not be quite so early in the spring when the crowns are set deep, but many advantages overbalance this possible disadvantage.