Plant Propagation: Secrets of a Green Thumb

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The propagation of new plants is one of the most exciting and rewarding aspects of gardening. Successful propagators are often referred to as having a “green thumb” but accurate observation, a genuine care for detail and a few basic rules can give almost any person this wonderful ability.

Propagation can be divided into several categories, each with their own special rules and conditions. The best-known method of reproducing plants is by seed. This is known as seminal propagation. The greatest drawback with seed grown plants is that they are all separate individuals and each have the potential for different growth and performance, especially if the seed is derived from uncontrolled pollination.

All other forms of propagation are vegetative. That is, new plants are struck from pieces of an already existing plant. Subject to certain modifications, connected with the technique used, this means that vegetatively reproduced plants will closely resemble the donor parent, because they are usually genetically identical with the donor plant.

The choice of the correct material for propagation is often a matter of experience. lt is an ability which improves as the gardener becomes more familiar with the plants he or she is working with.

Most plants freely produce seed. They are created by the fusion of male and female components. ln some cases, flowers may be self-fertile, in which case little variation may be expected (for example, seed taken from a patch of marigolds will give a new crop of plants similar to their parents).

However, many plants are self-infertile and need to be pollinated from another plant of the same species. This ensures a constant mixing of genetic characteristics and prevents inbreeding. Of course, uniformity of form will not occur when cross-pollination is employed.

Any gardener can make deliberate hybrids, simply by transferring pollen from one flower to another in the same or allied genera. A prior step in this procedure is to remove the anthers (the male part) from the receptive flower to avoid self-pollination.

The foreign pollen is simply introduced to the female part (stigma) of the flower and spread on its surface. The doctored bloom is then enclosed in a paper or cellophane bag to ensure no other pollen is introduced to the bloom. Petals may be removed to facilitate this procedure. If pollination is successful, the flower quickly dies and a seed capsule begins to develop.

Sometimes deliberate crossing can have unforeseen results. There was a case in Darwin, Australia, when a well-known nurseryman crossed Passiflora seemanii with P. maliformis. The former has beautiful blue flowers of thin texture and lightly banded stamens. The fruit is tasty, but thin skinned and subject to fungal infection.

P. maliformis has very dark flowers of extremely thick texture and a huge papery calyx that almost obscures the bloom. The stamens are extravagantly banded with dark purple stripes and the bloom has a thick sweet smell. The fruit are so hard-shelled that one needs a hammer to break into them.

The aim was to improve the fructiferousness of P. maliformis (which is a shy bearer) but retain the size shape and pulp content of P. seemani.

The cross was duly made, most of the seed germinated and a most amazing vine developed. The hybrid had leaves two or three times the size of either parent. They were cordate, (heart shaped) glaucous, (blue/green) in colour and provided a dense screen.

The flowers took on the very best characteristics of both parents and are also greatly increased in size. They developed large yellow calyces, supporting highly fragrant, ethereal blue flowers. The blooms resemble large blue waterlilies. The long stamens were heavily barred and cross-checked with purple stripes and blotches. However, the flowers were sterile – that is, incapable of ever setting fruit.

That was the unexpected part. In trying to obtain a new hybrid fruit, the nurseryman ended up with an ornamental vine of intense vigour and with beautiful flowers that created a dense fast growing screen.

When buying seed always try to get those presented in vacuum-sealed packets or containers. If packet seeds are not vacuum packed, particularly in our humid atmosphere, they rapidly loose viability and may be dead even before purchase. Regardless of origin all seed should be stored in the door shelves or crisper tray in a refrigerator until needed.

Sowing of seed can be a tricky procedure. Most fine seed like begonias, Weeping Ti-Tree and many native plants resent being covered. ln fact most will not germinate at all if the seed is covered.

A good seed raising mix is one-third shredded peat, one-third coarse river sand and one third finely granulated charcoal (25 mm mesh size). A little sieved compost may also be added.

When thoroughly mixed, this is placed in seed pans and lightly pressed in place.  Fine seed should be placed on the surface and lightly watered. Other seed can be buried to a depth of half the thinnest side of the seed. This ensures optimum germination.

Header image: © Nungning20

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