To make proper selection of plants for seed purposes the heads should be nearly mature. A common practice among large growers is to sow so late in the season that only a small percentage of the heads will be well developed when the roguing is done. Such plants winter with a smaller percentage of loss than when more mature, but the selection is likely to prove unsatisfactory. The gardener should know the time requirements of the variety from which seed is to be grown and try to have the heads nearly mature just previous to burying. On Long Island, most late varieties are sown about June 15, while those of the Wakefield type are not started until August. These dates for sowing would be too late for most northern states. The plants should not be grown in excessively rich soils, for very large heads do not winter well.
The roguing should be done as late as possible, discarding all heads not typical of the variety. Thorough winter protection must be given to both roots and tops. The plants may be buried where they were grown and the covering removed the following spring. In this way a crop of seed may be produced without two transplantings; but the more approved plan is to lift the plants and bury before there is danger of hard freezing weather. Various methods are used in providing winter protection. One of the best is to place three plants side by side in long trenches, made by plowing a furrow each way. The plants may be placed erect with the roots down, but better protection will be given by placing them at an angle of about 45 degrees. Two or 3 inches of soil is sufficient covering at first, although no injury will be done by 6 inches of soil if the weather is cool. After the ground is frozen, several inches of manure should be added, and in the coldest regions a foot might be used to advantage.
As soon as the ground can be worked in the spring the plants are removed from the trenches and set in rows 3 1/2 feet apart. Rather deep furrows are required to give the plants proper support, and ridging or staking must be resorted to later in the season when the seed stalks are developing. To allow the seed shoots to push through the heads with ease the tops are cut crosswise at the time of planting.
The seed stalks are cut about July 1, or when the pods have turned yellow, and placed in rows to dry. From two to four days are generally required for drying. When dry the stalks are loaded on a wagon, which should have a large cloth extending around and reaching over the sides of the bed, to prevent loss of seed.
A tight floor is necessary in threshing, which may be done any time after hauling from the field. The seed should be milled and thoroughly dried before storing. It usually takes from 20 to 25 plants to make a pound of seed, although frequently two ounces are obtained from a plant.
It is well known that cabbage thrives best in a cool, moist climate. For this reason its culture is largely confined to northern districts. When grown in the South, outside of the mountain areas, advantage is taken of the cool months of late winter or spring. The Danish Ball Head is rarely grown south of Pennsylvania, and at low altitudes in this state this variety is of doubtful value.
Successful crops of cabbage are grown on a great variety of soil types, the enterprise being developed to large proportions on soils ranging from light sand to heavy clays. It is largely a question of constant moisture (although good drainage is essential) and of abundant food. Excellent crops of early and late cabbage have been grown on sandy loams, often along mountain streams, where there is a large deposit of vegetable matter and a regular supply of moisture. Perhaps the largest crops of late cabbage have been grown on clay loams, well enriched by manure. The mountain glades of the Appalachian system seem to be well adapted to this crop. Danish Ball Head, which is the most limited in soil and climatic adaptation of all the varieties, succeeds well on the DeKalb series of soils in Pennsylvania. The reclaimed swampy glades in the mountains of West Virginia have produced large crops without manure or fertilizer, although these materials, with the addition of lime, increase the yields. A mellow soil which does not bake hard and which is well supplied with humus will generally produce satisfactory crops.