This section is from the book "The Gardener V2", 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.
This is a very beautiful and interesting group of hardy border and rock plants, which in bygone years was much admired and extensively cultivated in this country, but latterly it has been entirely neglected, at least in the gardens of the rich. It is rather astonishing that it should be so, Primulas are so fragrant, so beautiful in colouring, and so neat in habit; and the majority of the species, flowering as they do in spring and early summer, present a character so desirable, that one would think lovers of flowers, whether professional or amateur, could not easily forget or forgo. There are signs, however, of the old love being taken up again. Some beautiful varieties of the Cowslip and Primrose are found very useful in the spring flower-garden, for which they are very fit; and the catalogues of florists and seedsmen are swelling with new species and varieties in addition to many old and well-known sorts. The majority of Primulas are very accommodating in cultivation, adapting themselves to many kinds of soils and situations, but are most at home in sandy loams, deep and moist, but well drained and in moderately shady positions. They are easily propagated by seeds, cuttings, and division, the last being the simplest and easiest process where large increase is not an object.
In laying in first stock, seed is the best and cheapest way in the case of the varieties of Primula Auricula, Primrose, and Polyanthus, unless fine named sorts are wanted, when they must of course be purchased in plants, and by name, the same as with other florists' flowers; and the finer and more rare species must be got in the same way, because seeds of those are not always procurable true in this country. For a couple of months or more after sowing the plants do not require much room, and are liable to be destroyed by slugs and other pests whilst in the tender seedling state. A cold frame, hand-lights, or glasses, should therefore, if possible, be devoted to them, in which they will be more easily guarded against all enemies than if they were in the open ground. If many sorts are to be sown, small pots should be used to sow in, and they should be plunged in sand or coal-ashes. The soil should be sandy loam, peat, and well-decayed leaf-mould, in equal proportions, with plenty of sharp sand to keep the whole sweet and open. Sow thinly, and keep the soil regularly moist till the plants appear, when caution in watering will require to be exercised to prevent damping, to which Primulas are all rather liable in their first stages from seed.
As soon as the plants are big enough to handle, they must be pricked out thinly in pans, pots, or boxes, and returned to the frame, or set in a shady, warm, sheltered place, and well attended to with water, - taking care, however, not to allow the soil to become stagnant with too frequent waterings, which would very soon be followed by sickness and death to the plants. Primulas delight in moisture in the growing season; but a good sound watering at intervals, not daily driblets or sprinklings, is what they want. When the plants have made sufficient roots and bulk of leaves they may be transferred to their permanent quarters and well watered after planting, when they will need little more attention for the season beyond keeping them clean. If the seeds are sown in the end of March, the plants treated as above directed will bloom the following spring. In the case of getting up large quantities of Primroses and Polyanthuses, for the purpose of planting out in woods and suchlike places, the foregoing directions would be troublesome and expensive, as it is only meant for the more valuable and rare species and varieties.
The common varieties are best sown on a warm border in the beginning of April, in beds, broadcast or in drills, and, when fit to handle, planted out in nursing-lines in rich soil well manured with old hotbed dung. Cuttings are best put in in spring, when growth has fairly begun: the same soil as recommended for seeds is suitable for cuttings. Division should be done first after flowering is over, unless large increase of particular sorts should be desired, or when the plant is very weak and would obviously be invigorated by being divided immediately before flowering commences; in such cases everything should be done to prolong the growing period, and all flowers removed as soon as they can be got hold off. Under the name Primula veris, Linnaeus included the three forms of Primula most common in this country, - the Primrose, Primula vulgaris; the Oxlip, Primula elatior; and the Cowslip, Primula veris of modern botanists, being considered by him essentially the same for the purposes of science. But to gardeners and florists it is convenient to distinguish between the three forms, which are well marked and pretty constant in cultivation, at least Primula veris, the Cowslip. The common flower-stalk in this form rises considerably above the leaves, supporting an umbel of flowers; and in the single varieties, the corolla is small and cup-shaped - features that are lost sight of in the double varieties, or florists' Polyanthuses. Prom this form there are many varieties, some of which are most beautiful things in their season, and worthy a place among choice plants.
The commoner single sorts are suitable for planting in woods and on banks, and about the edges of masses of shrubs.