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 subject, it may be observed, is barely consistent with the title of these Notes. Only a very limited number of known species of Lobelia may strictly be termed hardy; but it is necessary once for all to state that the writer, in pursuance of the object of these papers, will bring-under the notice of the readers of the ' Gardener ' all such plants as he can recommend as available and proper for the adornment of the mixed border, rock work, and other similar uses, whether, as in the case of Lobelia, they require protection more or less in winter, or are quite hardy. '
Lobelia is rather an extensive family, composed of a few annual and biennial, and a large number of perennial herbaceous, and a few evergreen sulfruticose species. It is liberally distributed over many of the warmer parts of the globe, but in Europe and Northern Asia representatives are few and rare. Britain is favoured with two species, L. urens and L. Dortmanna; the former a very rare plant, having hitherto been found in one locality only - in Devon, near Axminster; and the other, being aquatic, and found in only a few of the lakes in the three great divisions of the Kingdom, may be regarded as a merely local plant in this country. The reputation of the genus for ornamental purposes is deservedly very high; there is indeed little contained in it that may be condemned as weedy or uninteresting, while of many species and varieties it may be correctly said they are unsurpassed for brilliancy of colouring and adaptability to every style of flower-gardening, whether rustic or refined, ribbon or panel, masses of one colour or mixtures of many colours, on any scale, small or great, from the humble patch in the cottager's mixed bed or border, to the thousands that adorn the gardens of the rich and luxurious.
But until very recently little has been heard and less seen of Lobelias in this country, except in so far as the justly popular L. erinus and its several excellent varieties, or the pretty annual L. gracilis or campanulata, have brought them into view. It is refreshing, however, to observe that the tide of popular favour is now fairly setting in the direction of the old-fashioned and long-neglected tall herbaceous species, whose striking aspect and sparkling colours are unfamiliar to the majority of young gardeners, but will be pleasingly remembered, either as pot or border plants, by those who can carry their memories back for twenty-five or thirty years. L. cardinalis, with scarlet flowers, and L. syphylitica, with light-blue or purple flowers, are both very old inhabitants of British gardens, and both are from North America. L. fulgens and L. splendens, both from Mexico, are more recent introductions, with scarlet flowers and dark-coloured foliage, but are less hardy in constitution than the two first-named species. Then came the purple speciosa, a hybrid of Scotcli origin between syphylitica and cardinalis.
L. ignea, more recent than either of the foregoing, was brought out as a species, but has little if any specific character about it; it is very near L. fulgens in appearance, and would pass very well as a variety of that species, with rather weak straggling habit, but most brilliant scarlet flowers and intense dark foliage. L. fulgens v. St Clair is a comparatively recent variety, of excellent merits, upright and stately in growth; the leaves are rendered somewhat hoary by numerous whitish hairs that are thickly studded over the dark surface, and the flowers are brilliant scarlet in dense spikes. L. syphylitica v. alba is a beautiful sort, but rare and difficult to keep, which has been occasionally seen, but always limited, and in the hands of only one grower here and there in the country. Occasionally, too, was seen in the past a dwarf variety of L. cardinalis, named nana, of the same colour as the species. But the foregoing list contains the sum of the colours to be found in this section of Lobelia till within three or four years ago, when the species, yielding to hybridisation under the hands of Messrs Bull of Chelsea and Henderson of St John's Wood, are now giving us numerous progeny, with colours previously unheard of among tall Lobelias. There are carmine, cerise, claret, magenta, pink, ruby, with many shades of purple and scarlet and crimson, while these are varied still more in certain varieties with white.
There is also in some sorts an increase in the size of the individual flowers, and there is greater variety in habit. Some varieties are dwarf and diffuse, others tall and strict; and in this respect there will soon, perhaps, be such diversity of character as will render Lobelias of this section adaptable to very general use in bedding-out. But there are other tall herbaceous Lobelias worth having, both on account of their own intrinsic merits, and the probable good results that would accrue from infusing their blood with that of species and varieties already in our possession. L. cœlestis, about 2 or 3 feet high, with clear azure-blue flowers, from N. America; L. amœna, about 3 feet high, with L. Kalmii, a foot and a half high, both blue-flowered, and from N. America; and L. verbascifolia, a large-growing tomentose-leaved sort With red flowers, from Nepal, are species of considerable beauty. Our own indigenous L. urens is no mean plant under good cultivation, and might if crossed with the showier sorts, introduce a hardier race. L. Dortmanna is indispensable where ponds, lakes, or sluggish streams must be furnished with select or choice vegetation; its pale-blue flowers drooping in slender racemes on the surface of the water, are very pleasing.
As subjects for the mixed border, nothing can surpass these tall perennial Lobelias; and it is astonishing that the species and the older varieties should ever have been allowed to fall into disuse for that purpose, for under good cultivation they are striking, bold, and handsome. Their cultivation is a very simple matter. From the combined influences of cold and wet the soft succulent underground stems are liable to perish in winter if left out of doors where they grow, unprotected; protection of some sort is therefore necessary. Some leave them where they made their growth till spring, protecting them with a mound of coal-ashes or any other available protecting materials; others lift them as soon as flowering is finished, and stow them away in coal-ashes or dry sand in sheds, under stages of cool plant-houses or in cold frames; and a friend of the writer, who was very successful in the cultivation of Lobelias, kept his roots in tubs of water under cover to prevent freezing; but the water, on account of its liability to become putrid, required frequent renewal, a circumstance, doubtless, that prevented my friend from making converts to this pickle-tub method.
My own experience is in favour of lifting the roots in autumn immediately after flowering is finished, dividing them, and potting the offsets singly in the smallest pots they can be got into, afterwards plunging the pots to the rims in coal-ashes in a cold frame. Liberal airing in favourable weather and protection during frost is all that they will need of attention and labour till the early months of spring. To do them thoroughly well, they must have an early start, and for this purpose a hot-bed, in which a temperature ranging from 60° to 65° can be kept up, should be in readiness to receive them by the second week in February. Examine and trim the plants, and transfer them to the hot-bed, not plunging them, but merely setting them on a bed of ashes. They will soon begin to grow, and will require shifting and constant attention to watering, but as yet very carefully. Continue to shift as required by the progress they make up till the end of April, when they should get their final shift and be transferred to a cold frame, kept close till they are inured to it, and afterwards carefully hardened off for planting out in the end of May. They are not particular as to kind of soil, but are very much so as to the quality.
Loam and peat and well-decayed stable manure in nearly equal parts, and abundance of grit of some sort to keep it open and porous, is a compost in which these Lobelias delight in pots, and the beds or borders that they are designed to occupy out of doors cannot possibly be made too rich for them. They are very impatient of drought when making their growth, and will absorb almost any quantity of water; it should not therefore be spared.