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.
An aromatic herb: a native of Siberia. It is used for flavouring various dishes. As a cheese herb, with mustard and cress, it is in request every day in the year. It requires a good deal of attention to keep up a stock of it, particularly as a good bit has to be taken up for forcing in many places. It must have a light rich soil and a warm corner. It is propagated by division of the roots in spring, when about starting into growth. The ground should have a good dressing of decayed hot-bed manure, be dug deeply, and the roots be planted in rows, about 1 foot apart each way. The crowns must be protected against slugs, which are very fond of the young growths, and eat them off as they appear. Keep the ground cleaned and stirred during summer. The stems may be cut and dried for winter use, but it is seldom asked for in this state when it is forced. It stands the winter better when the stems are left uncut till spring, and it is a good plan to strew some litter over the bed in winter as a protection against frost. Unless Tarragon is taken up and replanted frequently - almost every year - it is apt to die off, and it will be found advisable to keep this in mind when a good stock is required.
For forcing, it is better to have a stock in pots two years old, and then there will be no danger of a blank occurring in the supply in autumn, when the stems of the out-door stock begin to ripen off and get yellow. The roots may be lifted in November or December, and potted amongst good soil in 12-inch pots. Force gently during the winter; use the young shoots, but allow some of the stems to grow, and as soon as the bed outside begins to afford a supply in spring, harden off the pot-plants, and set them out behind a north wall during summer. Early in autumn they should be cut down, and the pots top-dressed, when they may be again introduced into heat as early as needful to keep up a supply, and another lot should be lifted in winter to succeed these the following year, while the older plants may be planted out. If taken care of, the same pot-plants will do for two or three years.
Wortley. J. Simpson.