The most successful asparagus growers of the old world have for centuries practiced seed selection. The experts of several hundred years ago may have possessed limited knowledge of the laws of plant breeding, but they evidently realized the importance of careful selection, and knew enough to select seed that would produce spears of enormous size. In the United States the growers who far excel the average in net returns to the acre invariably use selected seed, which they consider as important as high fertility and thorough tillage.
Large size and superior quality count for more than anything else in securing remunerative prices. These objects, therefore, should be paramount in the mind of the grower who would select his own seed. Vigor of stock is also essential, and it may be an advantage to take earliness into consideration.
Experienced gardeners seem to agree that the best seed is not produced until the plants are at least four years old. A greater age is sometimes recommended. The prospective plants for seed production are studied carefully for a season or several seasons, perhaps, and the observant grower finally decides upon certain ones that approach his ideals. They are free from rust, or practically so, the shoots are large and surpass the average plant in number. To be even more accurate, and certain of getting seed from the most prolific plants, some of the most promising specimens may be marked and numbered and the cuttings of each weighed for a season or two. It is just as important to choose high-grade male plants as it is to choose the best female plants. There may be several female plants to one male and they should be in close proximity to each other to insure thorough pollination. A stake should be driven at each plant to serve as a mark the following spring. The spears from all other plants in the field are cut and marketed as usual and only two or three stalks retained on each breeding plant. This limitation of stalks will produce stronger plants and larger seeds. Six to 10 inches of the tops and the ends of the branches should also be cut off to favor the development of better seed on the lower part of the plant, and if there is a profuse setting of berries, it is an advantage to remove some from the extremities of the plant.
The seed should not be harvested until fully ripe. When gathered in wholesale lots without the careful selection which has been described, the plants are cut, hung in the dry for a few days and then threshed. The chaff is next removed and the berries soaked in water for a day or two when the skin and the pulp may be readily removed by the use of a wooden block, followed by successive washings. Carefully selected seeds are stripped from the plants by hand, soaked for a day or two and the pulp removed by rubbing the berries between the hands or by the gentle use of a wooden block, after which they are washed, thoroughly dried and stored as other dry seeds. In the process of washing, the heavy seeds sink, while the light ones float and are poured off with the shells and the pulp. Further selection of large, plump seed may be made by screening with a mesh of proper size.