This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
More than three hundred years ago the Hollyhock came from China, and is still a garden favourite. One time, indeed, before other beautiful hardy rivals became common, great attention was given to the improvement of the Hollyhock, and specialists will recall such names as Chater, Bircham, Baron, Paul, Roake, and the Rev. Edward (afterwards Lord) Hawke as amongst those who took particular interest in the plant. In the middle of the nineteenth century - the '60's - Hollyhocks were at every exhibition, and were as popular then as the Sweet Pea is to-day. Owing to the great demand for the plant, it was propagated with the utmost speed in hothouses from seeds and cuttings, with the result that the constitution of a perfectly hardy plant was undermined and weakened. The plants throughout the kingdom and also on the Continent fell a prey to the terrible Hollyhock Disease (Puccinia mal-vacearum), which still appears in places every year, blistering the under surface of the leaves with its raised brown or yellowish pustules. The Hollyhock was therefore rendered hors de combat for many years, because the spread of the disease could not be checked. Consequently it dropped, and its place was taken by other plants in the meantime.
At the present day a great trade is done in the young plants in spring. These are raised from seeds sown the previous April or May, and when large enough are transplanted in rows about 1 ft. apart every way, in fairly good garden soil, and in open sunny situations if possible. Where a trade is done in particularly fine varieties, these are usually propagated by cuttings of the sturdy non-flowering side and basal shoots during the summer months. They are inserted in sandy soil in pots or pans or frames, gently watered in and shaded from strong sunshine until established, when they are allowed plenty of air and light. The tufts of old plants may also be split up into pieces, each having portions of root attached. Grafting of special varieties on to common stocks used to be practised, but in these days it would not pay for the trouble. Besides these methods it is possible to raise and flower Hollyhocks from seed the first year. The seeds should be sown in rich gritty mould in January and February in a temperature of 65° to 70° F. They soon germinate, and when large enough to handle easily are pricked out about 3 in. apart in boxes, or placed singly in 3-in. pots. They are grown on rapidly for a time, but are eventually hardened off gradually with plenty of air and a cooler atmosphere so as to be ready for sale in May.
For garden decoration, as bold masses in the border or in beds by themselves, Hollyhocks are very useful. They should be planted about 2 ft. apart, and as they are gross feeders the soil cannot be too rich, and at the same time well drained. When coming into flower they will benefit by occasional doses of weak liquid manure, or some proprietary manure sprinkled over the soil and hoed in where the plants are well established will help them considerably. To have a good supply of bloom open at one time, the tips of the flower stems should be pinched out. This will check further upward growth, with the result that the blossoms will open together.
There are many single and beautiful double varieties, varying in colour from the purest white to the deepest rose, crimson, mauve, magenta, and purple, and the brightest and softest of yellows; but of blues there is none. At one time specialists gave fancy names to their pet varieties, but nowadays they are designated by colour or by single and double varieties (fig. 209).
Fig. 209. - Double Hollyhocks.
In hot, dry seasons both Red Spider and greenfly are likely to be troublesome. They may be prevented by syringing the plants freely morning and evening with insecticides or soft-soapy water. The fungus already referred to is checked by syringing with liver-of-sulphur solution (1 oz. to 3 or 4 gal. of water) or by spraying boiling water over the foliage with a fine syringe. Badly infected leaves are best picked off and burnt immediately.