Hybrid Poplars Easy To Grow

Press, Issue 31095, 25 June 1966, Page 9

Hybrid Poplars Easy To Grow

TVIDELY spread through- ’’ out the northern temperate zones of the world, the poplar has always been an important tree in man’s economy, and, because of what we call the population explosion, the last 50 years have given the pop Tar an even greater importance.

In many parts of the world man is pressing hard on his means of subsistence. Agricultural output has to increase enormously if much of mankind is not to go even more hungry than it goes today. We are knocking down the world’s accessible forests faster than they grow under natural conditions. Our industry, our education and our standard of living require enormous amounts of timber—in the raw for building, as chipboard and veneers and as pulp and paper. For all these purposes poptars of one kind or another provide a hardy and fast growing material.

Break Through

The poplar’s real break through has come with the modern plant breeder’s ability to grow the tree he wants to suit a particular purpose or locality. All poplar species hybridise freely. Until man began to move freely about the world a couple of hundred years ago, the poplars of Europe, Asia and America developed their own local hybrids—the hardiest surviving to grow into pure stands.

About the year 1700 the American p. deltoides was brought to Europe and crossed with the p. nigra italica—the typical lombardy poplar so familiar to us. The progeny, known by the general name of populus x euramerica was a hybrid with more vigour than either parent and possessing the better characteristics of both; it had a straight, round trunk and a slightly spreading crown.

The typical euramerican hybrid is what we now call “robusta.” By breeding robusta again with other variants from both European and American stock, a much greater variety of form could be produced. When the Asian poplars, particularly the Chinese, p. yunnanensis, were brought in, then the number of possible varieties became infinite. Saved But a stand or forest of trees, each one differing a little from its neighbour—though all are poplars—is no use to timber merchant or sawmiller. Poplars were saved from this Infinite diversification by the fact that the better types grow very easily from cuttings. The breeder who hit on a good tree could reproduce its exact characteristics by planting cuttings of the new wood which is produced abundantly each year. These parent trees are called clones. Once the worth of a particular clone was established, it was given a name—generally of the district where it was

(Written for "The Press” by R. R. BEAUCHAMP)

grown. Thus you have such tongue twisters as populous x euramerica, serotina (the name of that particular cross), du poitou (the district where the clone was raised) The Italian breeders number their crosses—l 214,1455, etc. Countries which use poplars extensively like France, Holland, and Italy, have state departments which supervise the issue of pure bred stock to nurserymen. Our Department of Agriculture has a poplar nursery at Palmerston North which does this work; though, as yet, there is no legal compulsion to use its guarantee when selling trees. The growing of hybrid poplars is very easy. Six to eight inch cuttings of new wood, of average pencil thickness, pushed into well worked garden soil, will give a 100 per cent strike. If the soil is good and water sufficient they will grow six to 10ft in the first season. Weeds must be kept down and about midOctober all but the strongest shoots rubbed off. In the first winter the rooted cuttings are dug out with a sharp spade for transplanting to their permanent sites, where they should be set not less than 18 inches in the ground. The long tops will be very whippy and liable to

wind damage. If you cannot stake them on an exposed site then cut them back to a bud about a foot above the ground and let a single strong shoot come up again. For maximum growth, 15 to 18 feet in three years, either cultivation, spraying or mulching is essential. They respond well to super and ammonia in the spring.