This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
It has been said that a market gardener's stand should never be without Parsley (Carum Petroselinum). Parsley is one of the vegetables of which few growers can manage to dispose of any great bulk, except perhaps two or three growers in Bedfordshire. It does not therefore suit the grower who likes to crop his land with a few crops that can be sold in great bulk, and that require little trouble to grow or little business skill in selling. To keep a constant supply of Parsley, and get the most out of it, require skill and constant watchfulness in the grower, and alertness and push in the salesman.
To keep up a supply, three sowings at least are necessary - in March, in June, and in August. The seed is sown in drills 1 ft. apart. As the Parsley seed is a very long while germinating, it is a good plan to mix with it some seed of a plant that germinates quickly: Radishes or Lettuces are sometimes used for this purpose. Only a small proportion - about one-tenth - of the added seed is necessary, and then, not only are the rows marked for the hoers before the weeds get the upper hand, but the crop, whether of Radishes or Lettuces, can be taken without much injury to the Parsley.
Parsley does best in light soil with plenty of sand in its composition, and it cannot with safety be put upon the same ground again without an interval of a year or two. It is sent to market either bunched or loose in baskets. The period when it is most frequently scarce is from February to April.
Parsley realizes about 2s. per dozen bunches; and loose, 1s. to 1s. 6d. per peck, [W. G. L].