Another phase of the same practice, namely, the protection of plants which flower naturally during winter, has already been considered under the head of the Alpine House; but a good many perennials of larger growth than most alpines, suitable for an ordinary greenhouse, may be mentioned here. Adonis amurensis, a somewhat recent introduction, is one of these, and differs but little from the better known A. vernalis, though it is scarcely so fine a plant, but its bright yellow flowers are amongst the earliest of the year.
Christmas Roses (Helleborus niger) can fairly claim a foremost place in the winter list. These are not always easy to manage as pot plants. One of the most successful growers I ever knew was a farmer's wife, whose Christmas Roses were always to be envied. These used to divide their yearly cycle between a deep earthenware washing-pan, in which they flowered, and a shady border under a north wall, to which they were banished as soon as the flowers were past their best, but not neglected, for they received a generous mulch of farmyard manure and an occasional drenching with rain-water, not wholly free from soapsuds, during hot and dry summer weather.
When the buds had gained some size in the late autumn, the clump was carefully lifted without disturbing the roots and reinstated in the brown pan, whose winter station was on the broad windowsill of the best parlour.
Here, sheltered from wind and rain, the flowers opened, pure and fresh, in due season. No better system than that adopted by my old friend can be followed, though a broad, deep garden-pan, with drainage-holes complete, may be substituted as more fitting for the greenhouse, though it is doubtful whether it would prove an actual gain.
To prepare such a plant the root-stock of an old clump must be carefully broken up into pieces, each with growing buds and some of the black fibrous roots attached, from which the species derives its name. The only right moment to do this is just when the greening sepals show that the flowering time is over and active root growth is setting in, and these flower-stems should be cut away to prevent an effort to seed.
After planting the pieces, not too thickly, the pan should be plunged, preferably in a border shaded from midsummer sun, and the surface mulched to keep the roots moist and good. It is very possible that there will be no flowers the first season, as Hellebores dislike root disturbance. After the first year the plant should be turned bodily out of the pan into the border during the summer and replaced in autumn, which can be done with very little meddling with the roots.
Astilbe japonica, popularly known as Spiraea, is a true garden perennial, which flowers out of doors early in summer, and is valuable from doing well in shady places, but it is so universally grown as a greenhouse plant that this fact is generally forgotten. A. chinensis, which is quite distinct from the Japanese species, with which it must not be confused, flowers rather later in the open air, but answers well under pot culture. Its taller growth and branching, feathery flower-spikes make it a most desirable addition to the greenhouse. The handsome but tender foliage, as well as the pretty delicate flowers of the various species of Epimedium also, are never seen to better advantage than under glass, where they are secure from rough weather.
There are a good many well-known garden plants which may usefully be employed in the same way for the cold greenhouse. Orobus vernus is valuable for pots early in the year, when its clusters of blue-purple Pea-flowers are very spring-like and welcome. Several varieties of it exist, and it is easily raised from seed. 0. variegatus, which flowers later, may also be tried.
The large-flowered Forget-me-not (Myosotis dissitiflora) is a gem of the first water, and may very successfully be grown in pots or in zinc troughs about 4 in. wide as an edging for groups of plants to hide unsightly pots. These troughs may be made of any size and shape, and have been found extremely useful filled with growing plants of this Forget-me-not or of white Rock-cress (Arabis albida) in church decoration, especially for windows, being less perishable as well as less formal than many of the designs used for the purpose. Shelter in early spring is peculiarly acceptable to this Forget-me-not, as the first flowers are often injured by frost. It is a good plan to grow some spare plants in an outside border, that they may scatter their seeds, and to use these strong self. sown seedlings, which answer far better than cuttings, for potting in the autumn.
In Italy the large-leaved Saxifrage (S. crassifolia) is used as a pot plant in all sorts of positions-on terrace-walls, on the balustrade of a sunny loggia, sometimes even in the half-shadow of an over-springing archway. The pink clusters of flowers rise well above the thick oval leaves, and the good effect of the old-fashioned plant thus grown takes one by surprise. To get the ruddy flush of leafage which they will put on in full exposure, the plants must live out of doors, and be brought into the greenhouse only in the depth of winter. There is a charming white variety of this species very little known, and both should be noted.
Some of the Doronicums are bright and sunny-looking. The dwarf D. caucasicum responds quickly to kindly shelter, and opens its big yellow Daisy-like flowers very early in the year. The tall D. excelsum comes into bloom a little later. It is apt to flag in the hot spring sunshine, and must be kept as cool as possible.
Another favourite and good plant is our old friend Dielytra, now called Dicentra spectabilis. It is a hardy perennial, but in some parts of the country the succulent stems and sprays of graceful pink flowers are often damaged by late spring frosts.
Another very charming hardy perennial is the white form of the Peach-leaved Bell-flower (Campanula persicifolia). To get it to flower in early spring requires considerable forethought, as the foundation for the next season must be laid in the previous April, but the way to manage it is as follows : Good side-pieces must be chosen which show no sign of sending up flowering stems, or the plant will be in bloom before it is wanted.
These should be potted firmly in good loam, in 7-in. pots, and plunged at once in an outside border. In the autumn the pots must be transferred to a cold frame, like most other plants which are being brought on gently for early flowering, and later be removed to the greenhouse, where the spikes of pure white flowers will be very acceptable. There are many garden forms, single and double, of this Bellflower, of which the type is blue, but a very good one for the purpose in view is that known as the large white Cambridge variety.
The preparatory process thus sketched will be found useful for other herbaceous plants, and may be tried with modifications for any perennial which seems in the grower's fancy to be suitable and desirable. Heuchera sanguinea with its spikes of carmine-red, Tiarella cordifolia, the feathery white plumes of which are never out of place, though never so lovely as in their native woods, the long-spurred Rocky Mountain Columbines (Aquilegia ccerulea and A. chrysantha) are all wild flowers of the New World, well known now in our best gardens, but they may be pressed into the service of the cold greenhouse should circumstances suggest their use. It is a well-known fact that plants can be educated, so to speak, to change their time of flowering.
A species, for example, which flowers naturally in June, by an alteration of treatment and temperature may be induced to bloom in April. The following season, in all probability, with the same treatment, the flowers will appear a month earlier, until, instead of midsummer, that particular specimen gradually becomes accustomed to open its flowers in spring. This tendency to change of habit is a very useful one, and should be turned to the best advantage by the cold-house gardener.
Primroses of several different types are valuable in the earlier months of the year, and follow each other in obliging succession. Dean's hybrid forms of the common Primrose (P. acaulis) make pretty groups of many shades-pure white, lilac, and deep crimson being found amongst them, as well as the normal Primrose colour. In arranging these in a greenhouse it is well to group them in gradations of one colour, otherwise the variety is so great that they are apt to lose their refinement of character, which is never the case when care is taken in the juxtaposition of tones.
The fine race of Polyanthus Primrose may be used in the same way, and if there be no wild garden or bit of mossy woodland where they can be grown as Nature would have them, it is a moot question whether the next best way of enjoying these beautiful plants is not in the cold greenhouse, coaxed into flower a little in advance of their kith and kin out of doors.
Primula Sieboldi, of very different character to either of the above, is another elegant species, especially when the best hybrid forms are chosen, as the type unfortunately has flowers of rather an ugly shade of rose-purple, but this has been much improved upon by careful selection and inter-crossing.
This Primrose throws up its tall slender stems and clusters of six to ten large flowers well above the pale green leaves, and is very distinct. It is also better suited for pot culture than for the garden on account of the thin fragile nature of both flowers and leaves, which are, moreover, deciduous.
The creeping rhizomes, which are slender and not very noticeable, are apt to be dug up and lost in the open border, and therefore it is a good practice to divide and re-pot the plants as soon as the leaves show signs of dying down. The pans-for these are best for this Primrose-can be plunged in a shady place to take care of themselves until the time arrives in the autumn to remove them to the frame or greenhouse, when they will need nothing more than a little top-dressing. Auriculas, too, of the so-called alpine section, are very good, and it is interesting to raise seedlings both of Primroses and Auriculas, taking care in the first instance to buy seed of a thoroughly reliable strain, and afterwards, by rigorous selection and casting away of all doubtful and mixed colours, to work up a first-rate stock of one's own choosing. All these are common, everyday plants, yet a most effective greenhouse display can be made in early winter and spring out of materials such as these, with a few bulbs and hardy greenery to match.
It is more interesting still to grow uncommon plants. One such, not to wander from the Primrose, is a Javan species, which has been known for perhaps half a century to explorers by the name of the Royal Cowslip, but is, nevertheless, comparatively new to cultivation, and is still rarely met with.
The climate of Java is tropical, but it has lofty mountains, whereon, at an elevation of some 9000 ft., Primula imperialis is found in company with Buttercups, Violets, Honeysuckle, and other familiar English plants, choosing, however, only to grow in moist, cool spots, under the shade of bushes or in thickets.
As far as is known, this particular species is to be found in no other part of the world. To give some idea of this giant of its race, it may be said that it sends up a stout flower-stem some 3 ft. high, from a rosette of very large and long, Primrose-like leaves. The flowers, which are borne in whorls-in this respect resembling some other Asiatic Primulas-are of a shade of yellow, deepening into orange, peculiar to itself, and it is in all ways, when well grown, a fine and striking plant.
The difficulty has been to get foreign seed to germinate, but ripe seed has now been perfected by home-grown plants, and probably it only needs, like so many of the Primrose family, to be sown as soon as ripe to sprout quickly and freely. The Royal Cowslip may be given as a type of many another rare and beautiful plant which will adapt itself, under loving culture, to the cold greenhouse. Nevertheless, it takes some enthusiasm, no less than painstaking, to enable us to get off the beaten track of everyday garden routine and seek out for ourselves the far-off treasures of distant lands.