Seed may be sown very early in the season, and the plants can be brought forward in the manner usual with half-hardy annuals, but there is no necessity for this mode of growing them. Sow in April or May where the plants are to flower, on soil which has been abundantly manured to a depth of eighteen inches, and they will bloom in good time. To maintain the rapid growth, water must not be stinted in dry weather.
SWEET PEA
Lathyrus odoratus. Hardy climbing annual
The history of the Sweet Pea can be traced back for more than two hundred years; and it is almost as fascinating as an exhibition of the flowers. Recent improvements in this highly popular subject include an amazing diversity of colours, a marked increase in the number of flowers on each stem, and an extraordinary enlargement in their size. A modern list may run into hundreds, but those who grow every known variety find that there are many close resemblances, arising no doubt from simultaneous introductions by hybridists who have experimented on similar lines. Enthusiastic growers of Sweet Peas are no longer content with a limited number of named varieties, for it is obvious that in competitions where fifty or a hundred bunches have to be staged for certain prizes, a large and representative collection must be grown. For general garden decoration, however, and to provide sprays for the adornment of homes, the Giant-flowered class, offered under colours only, will continue to be extremely popular.
The change in character and the increased usefulness of Sweet Peas have necessitated a revolution in the methods of culture. The freer growth and more robust habit demand greater space than was formerly allowed. Instead of crowded rows of attenuated plants, producing a meagre return of small flowers, poor in colour, it is now the practice to prepare the ground by deep trenching and liberal manuring, and to give every plant ample space for full development both in rows and in clumps. In the ensuing paragraphs we outline the cultural routine which should be followed as nearly as possible by those who desire to insure a long-continued supply of the very finest flowers. But where circumstances do not permit of these recommendations being adopted in full, the details may be modified according to the materials at command and the requirements of the cultivator.
It is usual to commence the preparation of the ground in autumn. Trenching is of paramount importance, for the roots of the Sweet Pea require a considerable depth of good soil in which to ramify for the support of robust healthy plants capable of producing handsome flowers over a long season. Where the surface soil is shallow, care must be exercised to avoid bringing uncultivated subsoil to the top, and it is well worth incurring a little extra trouble to provide a sufficient depth of fertile material for full root development. Therefore dig out a wide trench and place the good top soil on one side. Then remove and discard the subsoil to a depth of twelve inches and, after breaking up the bottom of the trench with a fork or pickaxe, replace with an equal quantity of decayed manure, leaves, old potting soil or any other suitable stuff that may be on hand. Finally return the top soil to its original position.
The use of manure needs discrimination, and in fixing the quantity, as well as in selecting the most suitable kinds, due consideration must be given to the character of the soil. For light land, four barrow-loads of well-rotted farmyard manure per square pole will make an excellent dressing, but a rather smaller amount will suffice for heavy ground. In place of farmyard manure an unlimited quantity of leaf-soil, if obtainable, may be used, and it is also a good plan to dig in any available green refuse. Garden ground which for some years previously has been kept in a state of high cultivation by the liberal use of natural manure will not, as a rule, need further help in this direction, but it should receive a good dressing of lime. Indeed, any soil in which Sweet Peas are to be grown should contain not less than two per cent. of lime. The employment of artificial, as well as organic, manures is essential in any first-class scheme of cultivation. But here a word of warning is necessary. Nitrogenous manures in any form are harmful to the plant when applied in large quantities, and are liable to predispose it to disease, except on extreme types of sandy soil. Heavy ground should be dressed with seven pounds of basic slag in autumn and two pounds of sulphate of potash in spring. On light soils apply in spring four pounds of superphosphate of lime and two pounds of sulphate of potash. The quantities stated in each case are sufficient for a square pole of ground. Wood ashes (in a dry state) are also of great value, and these should be raked in a little in advance of planting out.
The special preparation of the soil just described entails the raising of plants in pots or boxes in readiness for transfer to the open as early as weather permits in spring. The finest flowers are undoubtedly obtained from an autumn sowing, and about the middle of September may be regarded as the best period for putting in the seed. This early commencement possesses the advantage of allowing ample time for the development of sturdy, well-rooted plants, which will not only bloom in advance of those sown in spring but will remain in flower for an unusually long period. Sow in light porous soil, and either three-inch pots, pans or boxes may be used. Place in a cold frame and keep the lights down until the seeds have germinated, but afterwards the frame should never be closed except during severe weather. There must be no misunderstanding on the question of air-giving. The Sweet Pea is almost hardy, and robust healthy seedlings, grown as nearly as possible under natural conditions, are wanted. Therefore to subject the plant to artificial heat will only defeat the object in view. A current of air should be admitted to the frame day and night, and the lights may be entirely removed on all favourable occasions. But the seedlings will need protection from excessive moisture, for if too wet at the roots they are liable to injury from frost. When four pairs of leaves are formed, stop each plant once, and after a little further progress has been made transplant singly into three-inch pots. Keep the pots in the frame, giving only such protection from hard weather as may be absolutely necessary, and plant out on the first suitable opportunity. In the South transplanting may be possible late in February or at the opening of March, but a month later will be safer in districts north of the Trent.
Those who for any reason do not find it convenient to sow in autumn may start the seed early in the year—from mid-January onwards, according to the district. The general principles described in the preceding paragraph apply equally to spring sowings, but it may be well to say that there must be no attempt to hasten growth by the application of a high temperature. A frame will afford all the protection necessary, and even a box covered with glass and placed in a sheltered spot will be found serviceable for raising seedlings.
Before planting out, the top soil of the ground prepared in autumn must be well worked and made friable. The disposition of the plants, and the method adopted for staking them, will, to a great extent, depend on the precise purpose for which the flowers are required. For garden decoration single rows answer well, and the plants should be spaced one foot apart. Or, if preferred, put out in clumps of three to five plants, allowing a diameter of from nine to fifteen inches. Carefully remove the plants from the pots or boxes in which they were raised, disentangle the roots and shake them quite free from soil. Make a hole of the necessary depth, and allow the roots to descend into the ground to their full extent, which may be as much as two feet in the case of well-grown specimens from autumn-sown seed. Give support immediately with well-branched twigs, and it is important that the plants be kept perfectly upright. Finally stake with bushy hazel sticks eight to ten feet in height, or taller still where the ground has been generously prepared.