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.
In very dry seasons mildew among Roses is often prevalent, while in wet cold seasons they often suffer from the same scourge. This need not be wondered at, as any plant which suffers at the root from drought and heat, or from wet and cold, will fall a victim to disease. So with Roses when mildew, red-spider, and other pests appear; we may safely say that the supply of food from the roots is checked in some way. Certain soils are more productive of disease than others, and I was struck with this idea lately, when visiting some gardens in this county. Last year their Peas suffered severely from mildew, and this year they have done the same. Last season's drought was intense; this season we have had the opposite, extreme wet and cold, hence opposite causes giving the same results. [Medical men tell us that chronic indigestion is often caused by want of proper food, irregularly supplied, or too much food of too rich a character. A medical gentleman lately told me that he meets with more cases of disease and death from too much eating than from too much drinking, but denounces them both in the strongest terms.] By way of illustration: two years ago I made an addition to the already fine collection of Roses here; the border in which they were to be planted was composed of soil of the poorest description.
Plenty of good loam was trenched down, manure added in abundance, and when the plants were placed in their position, some good turfy loam was laid among their roots, and the whole finished up with a good mulching. The plants grew with great vigour the first year, and flowered satisfactorily. Last season they were all that I could desire. The drought was severe, but was overcome by giving the border good soakings of water from the stable cesspool, and good drenchings overhead did the rest: many of the shoots were like walking-sticks - a friend took the trouble to measure a shoot of a "Charles Lefebvre," and its length was 9 feet. However, towards the end of autumn, growth suddenly stopped - mildew appeared in considerable force; and this season, though the Roses have flowered well on this border (but nothing in comparison to what they have done in a Rose-garden some distance off), mildew is not to be seen in the Rose-garden, but on this border mostly every plant is infected. The cause is easily got at. This border of Roses last season made root in proportion to their wood, and to get away from the scorching sun of last year they pushed down through the good soil into material where starvation has commenced.
We intend to lift the whole of the plants (some hundreds), add fresh soil to the borders, and when the holes are made for the roots, a turf will be placed, grassy side down, trodden, and a good spadeful or two of earth of a kindly nature placed among the roots. If root-pruning is necessary, it will receive careful attention: a good mulching will finish the work. This "hint" is chiefly intended for beginners, who may be perplexed at present, or later in the season, by seeing the leaves and stems of their Roses coated with a substance like white dust (mildew). But if the plants are doing well, let well alone. M. Temple.