This section is from the book "The Gardener V1", 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.
Although some of the older varieties of double Chinese Primulas, notably the old white, are common enough, they, with few exceptions, seldom receive that amount of attention and good culture that their intrinsic worth merits. In too many greenhouses and other places at the present time, are they to be seen dragging out their existence, sometimes undisturbed in the same pot for years; while their more showy but really less valuable relations, the single varieties, receive the best of treatment. Even the old double varieties when well grown, not only form very attractive plants, but are also more serviceable for decorative purposes than are the singles; of late years, however, much attention has been paid to their improvement, and the result is a great increase in their number - all more or less superior. Mr E. Gilbert has been particularly successful in this work, and has received certificates for several of his varieties from the Royal Horticultural Society. The whole stock of them has passed into the hands of the Messrs Osborn & Sons, Fulham Nurseries, London, by whom they will shortly be distributed.
I saw them as grown and exhibited by Mr Gilbert, also growing and flowering in the above Nurseries, and in both instances was much struck with the very marked improvement effected, both with regard to the size and beauty of the trusses and blooms, and also in their evident robustness. The best white-flowering variety among them is the White Lady; and the Princess, white, slightly blotched with red; Marchioness of Exeter, white, spotted with pink (a fine flower); Mrs A. F. Barron, blush, slightly striped with red; and the Earl of Beaconsfield, a good crimson, - are all really sterling novelties.
Double Primulas are decidedly the most serviceable as cut-blooms, as they travel well. Individual blooms are largely used in bouquets, etc, but do not, I am bound to admit, always keep quite so fresh as one would wish; but from what I have seen of the newer varieties, they, in all probability, will keep better - the flowers being of a greater substance. The plants are propagated by division soon after blooming time; the offshoots with a heel attached being placed singly into small 60-pots, steadied - that is, lightly tied to small stakes, and placed in a moderately brisk, but not too moist temperature, till rooted. The soil used is about equal parts of fibry loam, and either peat or leaf-mould, with a good addition of silver sand and charcoal. When repotting, less peat or leaf-mould may be used, and a little thoroughly-rotten dung substituted. A good place to grow them in is on the back shelf of a stove, as they require heat till well established; after which, the temperature of an intermediate house is the most suitable for maturing their growth and afterwards for properly developing the bloom. Avoid large shifts when potting, and use clean and well-drained pots - the 5-inch is a very serviceable size.
Many off-sets rot in the striking-pots from- being put in too deep; and deep potting, deficient drainage, and careless watering, kills many that have survived that critical period. Doubtless they are sometimes well grown in cold frames, etc. treated similar to the single varieties, but more often not; and possibly for this reason are discarded, as being either too difficult or else not worth the trouble to grow. Where the cool treatment has failed, try what a little heat will do. W. Iggulden.