This section is from the book "The Gardener V3", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
The Parsnip is a native of Britain, and is most frequently to be found in its wild state growing in loamy soils by the waysides in England. In its wild state the roots are generally small, forked, tough, and have a rank taste. It has been cultivated in British gardens for a long time, but not so extensively as in the Channel Islands and in France, where there are soils peculiarly well adapted for its growth. In these places it sometimes attains an enormous size - 3 feet in length and 4 to 5 inches in diameter.
The soil most congenial to its growth is a moderately light loam, deeply trenched, with the soil principally near the bottom of the trenches. In working the ground, it should be thoroughly pulverised, and all large stones removed where they abound. When a piece of light suitable soil is awanting, it is a good plan to make deep holes into the soil with a large dibble, in lines 2 feet apart, and 8 inches between the holes. Some light rich compost filled into the holes, and a few seeds dropped into each, and in due time thinned to one plant, gives an excellent crop of this root in soils which are otherwise not adapted to its growth. But the most effectual way that ever I have adopted for the successful culture of roots such as this, and Carrots, Salsafy, etc., in clay soils, has been to burn the greater portion of the heaviest part of the soil, mixing it when burned with the best portion of the staple, adding at the same time a quantity of leaf-mould and light gritty soil, such as road-scrapings, etc.
The end of February or first week of March is a good time to sow for the production of line roots, and on rich soils the drills should be 2 feet apart and 3 inches deep. It should, however, be borne in mind, in the culture of this vegetable, that a soil highly gorged with manure -though such with plenty of room will produce immense roots - does not produce them so finely flavoured as when the soil is less rich; hence the reason why it is desirable to place the manure deep in the soil, to produce a direct downward growth in the roots than would otherwise be the case. Medium-sized roots are invariably the finest, from the rank taste which is peculiar to Parsnips both in their wild state and when over-stimulated with manure.
The after-culture is very simple, consisting of thinning the crop to about 8 inches between plants, keeping the ground free from weeds, and well stirring occasionally between the rows. The Parsnip being much hardier than the Carrot, and best when newly dug out of the ground, a portion of the crop should be left in the ground when the other portion is dug up, usually about the beginning of November. Those lifted keep freshest when packed in moist sand, and those left in the ground can have some loose stable litter strewn over them, so that, should it be frost when it is necessary to lift them, it can be easily done.
The old "Hollow Crowner" and more recently introduced "Student' variety are the best. I find the latter the cleanest grower of the two, and less subject to forking. This root is much more extensively cultivated and consumed by the cottager in England than in Scotland. It is considered wholesome, and, when properly cooked, is palatable and nutritious, as it contains a good deal of sugary matter; and when slowly roasted in hot ashes, it becomes nearly as farinaceous as the Potato. The English labourer looks upon it as one of his choicest roots; and boiled and eaten along with his pork or bacon in winter, it forms a very desirable variety of vegetable.
It was strongly recommended as a substitute for the Potato, when that king of vegetables was so critical a crop. But although the Parsnip is undoubtedly a hardy and tolerably nutritious root, it is not likely ever to become very extensively used, as soils best adapted to its growth are likewise best for the Potato, which, so long as it remains what it is, can never be superseded by any known root-crop. The Parsnip is, however, generally cultivated in all gardens of any consequence, and is in considerable demand through the winter months.