This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
The treatment of the Passiflora is very simple. It requires rich but porous soil, which may be prepared by mixing leaf mold, perfectly decayed sods from old pasture grounds, and well-rotted cowdung together, with the addition of some sand. Peat, sweetened by long exposure to atmospheric agencies, may be substituted for leaf-mold. The pots should be comparatively large; sufficient drainage is important. During the growing season the plants need much water, and are benefited by often repeated syringing; in the winter no more water must be given than is absolutely necessary, especially when they are kept in a rather cool temperature, otherwise the roots will suffer. They must be repotted at least every spring. A temperature varying between 45° and 60° Fahr. is suitable to all kinds. If the temperature is low, but moist, many kinds suffer from mold at the joints, by which they are injured very much. Some kinds stand our winters when growing in the open air, f. i ., incarnata. P. caerulea is hardy in northern Germany, when covered up a little.
In this country I never succeeded, even with the utmost care, to keep it alive in my grounds.
Passion flowers grow very easily from the seed in a hot-bed, or even in a warm room. To open them a little with a penknife before planting, as recommended by some, is unnecessary, for they germinate without the least difficulty.
Layering is always successful, but very seldom practiced, as cuttings will grow with certainty. They are taken from young shoots before the wood is too firm and old; if it is too succulent, the cuttings decay instead of forming a callus and making root. In long-jointed kinds two eyes are sufficient; in short-jointed,/. i.,P. kermesina, the cuttings are made from two to four inches long. They require very sandy, light soil and bottom heat. Keeping them in a close atmosphere assists the process of rooting very much.
Pieces of the root, provided they are not too thin, grow, if similarly treated, with facility. The best time for making cuttings is the spring; in a propagating - house they strike easily in the winter.
Passion flowers may be grafted according to all the known methods; bnt as grafting them presents not the least advantage, it is only done occasionally by amateurs. There was a time when I placed some confidence in it for certain purposes, but I soon gave it up.
Very important, however, is hybridization. We owe many very beautiful varieties to it, /. i., P. caerulea - rucemosa (P. caerulea and racemosa G. princeps), alata-caerulea (alata and caerulea), Loudoni (kermesina and princeps), etc. The anthers as well as the pistil being so prominent in the Passion flower, any child may perform the operation with success. It is advisable to remove the anthers of the flower to be impregnated with the pollen of another kind as soon as the flower opens, and a little later, when the pollen appears to be in the right condition, to cut off the whole flower, or a single anther, to touch with it the pistil of the flower to be operated upon. If the operation has succeeded, the fruit will soon commence swelling, and will protrude from the decaying flower. When the fruit is - according to the kind - of the size of a filbert or of a walnut, the decaying floral leaves, etc., and the remnants of the calyx, must be carefully removed, so that the fruit is freed from everything surrounding it, otherwise it is sure to drop prematurely, its footstalk and tube decaying along with the soft, succulent floral leaves.
This is the only means to insure the ripening of the fruit.
I am not aware that this all-important fact is mentioned in any of the books on horticulture; but I remember how often and how sadly I have been disappointed before it occurred to me to resort to the expedient just mentioned.
I have very rarely obtained ripe seed from the common P. caerulea, oftener from P. princeps and P. kermesina, and a few others. But there is a kind so ready to be impregnated by the pollen of almost every other kind, that I wish to call the attention of those interested in the matter to it. It is the P. caerulea - racemosa, and a lighter variety of it. Both, it is true, are hybrids themselves, yet they produce hybrids with so much facility and certainty that it is astonishing. I have raised from it a very large number of hybrids, some of which I flowered before I left Germany. One of them was exquisitely beautiful, its color being snowy white and its growth compact. I neglected naming it, and so it may have been lost.
As P. cserulea - racemosa itself is one of the finest kinds in every respect, nothing better could be selected for the mother plant. P. discolor or Maximiliana takes also the pollen of others very readily; but as its flower is rather insignificant, it is for the purpose of hybridization much inferior to P. cserulea - racemosa.
Pruning in the fall, and pinching during the summer, are essential in the management of the passiflora. I never saw any injury arise from very severe pruning. The flowers are produced on young shoots, often protruding directly from very old wood. If not cut back annually very severely the Passion vines will soon become unsightly, bearing their flowers at the end of long, naked stems. If not pinched in during the summer as often as young shoots need it, to prevent them from growing too long and slender, a number of kinds will not flower at all, when grown in pots; when, on the contrary, frequently pinched, the plants will be effectually checked and compelled to make new shoots, which will soon show flower buds. In this way I proceeded in flowering even Tacsonia mollissima and Pinnaetistipula, two kinds that have rarely been seen in bloom, except when growing directly in a border of a green-house. Those which I flowered grew in the open air.
Severe pruning and pinching are also the only means of dwarfing Passion vines. This was a favorite object I had in view when I devoted so much time to their cultivation. Some kinds are, with a little at-tention, easily dwarfed, /. i., alata, alata superba, quadrangularis and its varieties. P. insignis and Decaisneana, also phoenicea, kermesina, princeps, and Loudoni, are a little more refractory, but yield to energetic perseverance. Caerulea, however, lauri-folia, maliformis, and the like, baffle very often the cultivator's well-planned exertions.