Playing Around With Stems

Top Doggery

My pear trees look as if a giant spider went on a drunken frolic among the branches. Rather than fine silk spun in an orderly web, strings run vertically from branch to branch and branch to ground. Yet there is method in this madness. Mine.
 
As I spell out in my new book, The Ever Curious Gardener: Using a Little Natural Science for a Much Better Garden, plants produce a natural hormone, called auxin, at the tips of their stems or at high points along a downward curving stems. This hormone suppresses growth of side branches along the stem, allowing growth from a bud at the stem tip or high point be the “top dog,” that is, the most vigorous shoot.

Within any plant a push and pull goes on between fruiting an stem growth. Both require energy, which the plant has to apportion between the two. The more vigorously growing a stem, the less fruitful it is.

All this talk of hormones and inherent stem vigor is more than academic; it can translate into delicious fruits.

Pear trees tend to grow very vigorously, especially in their youth, with many vertically oriented branches. A certain amount of stem growth is, of course, desirable; leaves are needed for harvesting sunlight for energy and stems are needed on which to hang fruit.
Tied branches in British orchard

Tied branches in British orchard


But pear trees, especially in the youth, tend to put too much of their energies, too much for me, at least, into stem growth. The result is that they can take long time to settle down and begin bearing fruit.

Hence, the strings. I can change my pear trees’ habits by merely tying down branches, reducing the effect of that auxin so that growth is more uniform along a length of the stem. And, as important, slowing growth nudges the energy balance in the direction of fruiting.

Branch bending

The one branch on each young tree that I do not tie down is the main vertical stem, which is the still developing trunk off which grow the main side branches. I want this stem to keep growing upward. Also, I have to be careful not to create a downward arch when tying down any stem. You know why: a very vigorous shoot pops up from the high point in that arch.

More Fruit or More Growth?

Branch bending is not only for coaxing a tree into fruiting. On young branches, it creates a wide angle between a branch and the developing trunk. Wide angles here have been shown to result in good anchorage, sturdy side branches that can carry a weight of fruit.

Suppressing the vigor of side branches also ensures that they won’t compete with the developing trunk, which needs to be top dog.

And using string to play around with plant hormones isn’t needed on every fruit tree. At the other extreme from pear in its growth and fruiting habits is peach. Peach is naturally very fecund, and becomes naturally so at a very young age.

One reason for peach’s fecundity is that it bears all its flowers and fruits along stems that grew the previous season. Every year new stems grow that bear flowers and fruits.             

Beauty, Fruit, and Fun

All this concern with auxin, vigor, and fruiting comes most prominently into play with espalier, which is the training of a tree to an orderly, often two dimensional form. The tracery of the branches themselves adds to the decorative value of the plant.Pear espalier

Fruiting espaliers, besides being decorative, produce very high quality fruit. Pruning and branch bending maintain a  careful balance between yield and stem growth, and the form of the plant allows leaves and fruits to bathe in sunlight and air.

Asian pear espalier flowering

5 Comments

  1. Diane
    Posted June 1, 2018 at 7:25 am | Permalink

    Perhaps this explains why my 5 year old pear trees have not flowered yet? They are growing rather upright, difficult to prune or get a handle on…I have a Tyson, Golden SPice and a Hudak from St Lawrence.

  2. Nancy
    Posted June 1, 2018 at 11:26 am | Permalink

    Can I do this on a Chamaecyparis obtusa ‘Splitrock’ that I want to fill out horizontally and not vertically in front of some very low windows. I weighted down the one long branch during the winter, which was the main branch, but it is gradually rising again. And I wasn’t aware that it should be in a downward arc. Can I just keep tying various branches to keep it in a shape I want without damaging it long-term? It’s a beautiful plant, just too tall. I’m assuming I shouldn’t prune back the main branch.

    • Posted June 8, 2018 at 11:16 am | Permalink

      I think yes, probably. A downward arc will promote vigorous shoots from the high point of the arc. What you probably want is non vigorous growth along the bent stem, in which case keeping the stem horizontal rather than arched would be better. Or at a slight upward angle if you want faster growth of the bent branch.

  3. Beshia
    Posted June 13, 2018 at 9:12 pm | Permalink

    I have a pear tree that is very very tall (about as tall as a 2-story house).Two years ago it had many fruits but to high to harvest. This year there’s no fruit at all. I am considering the option of cutting it down. What would you recommend I do?

    • Posted June 14, 2018 at 10:17 am | Permalink

      Don’t cut it down if the pears taste good. Lower the tree over a number of years by making one or two large cuts low in the tree and then selecting new stems from those that sprout near the cut for the future framework of the tree. (More about this, of course, in my book THE PRUNING BOOK.) And then prune it annually and bend branches to keep it from getting to tall again.

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