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.
To succeed those planted either at the base of a warm wall or under hand-lights, as the case may be, towards the end of February or early in March, according to circumstances, more of the autumn-sown plants should be planted on a sheltered border. This crop is a valuable one, and well repays a little extra trouble. The soil I find most suitable for Cauliflowers generally is a rather stiff fresh loam, in which has recently been dug a liberal quantity of half-decayed manure. They will not "take hold" of a soil that has long been heavily manured and lightly dug, and from which comparatively light crops have long been taken. Bastard trenching is the best antidote for such a poisoned soil. If there is any likelihood of the plants moving badly from the boxes or frames, it is advisable to pot some of the strongest singly into 4-inch pots, placing them on shelves in a warm house, in a few days returning them to a cold frame to harden off, and planting out before they are root-bound. Choose a dry time for planting, make the soil firm, and ram it well about the plants with the back of the trowel, as loose planting encourages premature heading-in, or "buttoning." Eighteen inches apart each way is a good distance to plant, unless extra large heads are required - which for ordinary purposes are a mistake - and some of the smaller new early kinds may be planted still closer.
If the plants are well hardened, not much protection will be needed; but severe frosts may be warded off by covering with 6-inch pots, with clods of earth over the drainage-holes; and branches of Evergreens may also be used. Neither, however, should be used to excess, and only when severe frosts are anticipated. Liquid manure, applied when the heads are forming, will materially assist them, and should be followed up if large heads are required. Moulding up before the plants are large serves to steady them, and also tends to preserve the moisture about the roots. The weaker plants in the frames or boxes may, at the end of March or early in April, be potted up, or transferred direct to the garden, - planting half the batch, if possible, on a warm border, and the remainder in the open, thereby prolonging the supply. If autumn-sown plants are scarce, seed should at once be sown in pans or boxes, and placed in gentle heat. (I prefer the shelves near the glass in a newly-started vinery.) The soil should be light and fine, the seed sown thinly; and great care should be taken not to syringe the seedlings, as their very brittle stems are easily broken - this being the cause of whole batches damping off in an apparently unaccountable manner.
The seedlings should be potted, or be pricked either into boxes or a frame, over a slight hotbed, - be grown as sturdy as possible, and planted out before they become crowded. They will move out of a tine, light, leafy soil better than a coarse soil. Such varieties as Veitch's or Carter's "Extra Earlies," Dean's Snowball, and Dwarf Erfurt Mammoth are suitable for the earliest crops; and to follow these, I can recommend Carter's Mont Blanc, Sutton's King of the Cauliflowers, and Dickson's Eclipse, - which, if sown at the same time, will "turn in" in the order named. By varying the sites, and planting frequently, a good supply may be maintained with one variety - none in this respect being superior to Dean's Snowball.
Taking these for instance : if in the spring we have a good batch of autumn-sown plants, some of the strongest are planted in warm sheltered spots as previously advised, others on warm borders more in the open, and the remainder are planted on a north border. About one sowing of a main-crop variety on a warm border, early in April in our case, or on a gentle hotbed in colder districts, and the plants grown on a tolerably rich, open quarter, would then be sufficient to maintain the supply till the earliest Eclipse, or even Veitch's Autumn Giant (autumn-sown), are fit for use. This season autumn-sown plants are scarce, and therefore more plants were raised under glass for both the open ground and the north border. One of the best summer varieties is Sutton's King of the Cauliflowers, and it is equally good for the autumn, especially if grown on a north border.