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.
This valuable border-plant is fast rising in the estimation of the generality of horticulturists, which is not to be wondered at, considering its great usefulness as a border ornament alone. Great as are its merits as a mixed border-plant, the fulness of its beauty is much more apparent when figuring in groups or ribbon-borders in the flower-garden proper. There its graceful semi-pendant spikes are most telling. The Pentstemon has the further recommendation of being most suitable for bleak localities: it will grow and flourish in perfection where Geraniums would prove worthless - defying alike wind and rain.
In the different species of the genus there is a strongly-marked diversity as regards height, vigour, colour, and even hardiness. All its species are natives of America, although somewhat widely separated in their geographical distribution. From amongst the oldest known kinds we may enumerate: P. lrevigatus, a native of North America, introduced into Europe in 1756; P. pubescens, from the same country two years later; P. campanulata we had from Mexico in 1793.
The autumn is perhaps the best period of the year to sow Pentstemon seed. Autumn-sown plants are more vigorous, and they will flower more profusely the following summer. The seed ought to be sown in pans or boxess in light soil, then placed into a close frame without artificial heat, keeping the soil rather dry throughout until the seedlings appear. They may then be placed on a shelf close to the glass in a greenhouse for the winter, under which conditions very little attention is recpiired further than a little water now and then, until the spring has somewhat advanced. When more rapid growth commences in the seedlings, they should be potted singly into small pots, and encouraged to grow freely by every means, so that they may be strong plants at planting-out time, and that they may also flower the sooner.
Plant them out into beds in lines 1 foot apart each way. This is quite enough space for proving seedlings, and ascertaining which of them are worthy of being multiplied.
It is generally found that numbers of young sprouts make their appearance on the main stem a little above the soil. These make the best cuttings; they root more freely than when taken from lateral growths. Remove them from the plant when they are about 2 inches long, and have them dressed and potted in the ordinary method of putting in cuttings. They will root freely inside a shaded cold frame when kept close, with a rather moist atmosphere. When rooted, pot singly into 3-inch pots; and as soon as these are filled with roots, shift them into two sizes larger pots rather than have them get pot-bound before planting out.
A richly-manured free soil will be found productive both of vigour in the plant, and also quality and quantity of flower. The more robust growths should be supported by means of neat stakes that reach some distance up the stem; but these stakes ought not to reach so high as to interfere with the natural drooping grace of the flower-spikes. The tallest varieties should be selected, and made to do duty in the centre of the bed when a group of sorts has been determined on, bounding these with a ring of those less tall or vigorous in their habit. This forms an excellent bed without the aid of other kinds of plants. Nor is it advisable to plant too closely together; 15 inches apart both ways will suit strong growers and 1 foot the weaker ones.
Some of these are truly remarkable advances on known sorts, others none the less acceptable for the new shades, with other essential points of quality sustained as a matter of course.
Omega Niger, throat purplish white, streaked maroon, one of the darkest, quite a novelty. Little Pixie, purplish crimson throat, pencilled white, another novelty. Densa (dwarf), colour bright scarlet, deep crimson throat pencilled with white. Hugh Austin, light blue, white throat, stained dark rose, extra. Tribune, dark rose-purple, like Mazeppa. Wonder, colour light rose-crimson, pure white throat, veined pure, fine, open. Lomaria, pure white, slightly tinged rose, fine spike, profuse bloomer. W. M. Dolben, purplish red, the throat stained chocolate on the lower part, upper portion white, lobes streaked and spotted chocolate, splendid.
A. St Clair, light carmine throat, brushed, shining purple, distinct and fine. Mrs Rose, clear red, with pure white throat. Floribunda, white throat, bordered brisk red, fine. Eobert Fenn, a splendid sort, very distinct, throat plum, with purple tubes. Stephen Wilson, pale mauve, throat white, well expanded, solid perfect flower.
Agnes Laing, deep rose, clear white throat, excellent spike, flowers perfect. Amabilis, purple, throat crimson, extra. Black Knight, deep maroon, throat broken with white, striking and bold. Bridesmaid, French white, great spike, novel and fine. Delicatissinmm, white, tinged rose pink, grand spike of perfect flowers. George Sand, reddish purple, fine. Henry King, brilliant red, throat deep, white shaded red in detached streaks, fine. James Rothschild, massive, widely expanded blossoms of reddish purple, with pure white throat, one of the cream. Lady Boswell, has a handsome spike of rose-pink flowers, throat white, with a well-defined margin of carmine rose, extra. Standstead Rival, scarlet crimson, throat white, delicately pencilled, deep red, grand spike of perfect flowers. W. P. Laird, pale blue, white throat, fine spike, extra. Snowdrop, pure white, most distinct, should be in every collection. Rosy Gem, white throat, ground colour deep rose, very pretty. A. Kerr.