This section is from the book "The Gardener V3", 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 the March number of the ' Gardener,' "Reader" refers approvingly to the above. Probably, had he seen it as grown by Mr Taylor at Longleat, he would not have dismissed the subject so briefly - commendable, though difficult to practise, as brevity undoubtedly is. Guillon Mangilli is a winter-flowering variety of which it is impossible to write in too glowing terms, as by a little trouble it is possible to have an abundance of large trusses of semi-double, rosy-crimson flowers throughout the winter and spring months. At the present time, at Longleat, the plants are arranged in forcing-houses, in which Kidney Beans, Tomatoes, and other heat-loving plants are growing. They are disposed thinly, or otherwise the growth made would be too succulent - the aim always in view being to keep them as sturdy as possible. The majority of the plants are flowering for a second season in the same pots (principally 10-inch), not having been cut back at all. During the summer they are placed, but not plunged, in a sunny spot, kept watered, and all bloom pinched off.
The result is a sturdy growth which will flower in heat, without becoming drawn and weakly - always supposing the plants receive plenty of space and light.
Let me advise those who are in the habit of stocking some of their houses with large old Begonias, Coleus, etc, which frequently are of but little value, to substitute a few large, well-prepared plants of Guillon Mangilli - to which may be added Madame Thibaut, pink, and Madame Baltet, white, securing from them a quantity of bloom, useful alike for home use, or packing for travelling. W. I.
[We grow this Pelargonium in quantity, and find it very useful. A splendid free winter flowerer is Mrs Leavers, single. - Ed].