Tuesday, August 31, 2010

Pruning to renew growth, shape

The Twisted Willow trees and the Harlequin trees that we made in the spring need a bit of maintenance to keep looking their best.
You want the plants to appear like a tree - with a trunk and a crown - but as the rods that we planted start to root and grow, they will naturally set shoots along the length of the rods. The shoots on the "trunks" of the trees have to be pinched off during spring and  summer to keep the shape of the trees while the shoots in the top are allowed to grow. If you fail to do so, you will end up with a very bushy shrub in the pot.
Keeping the twisted trees (from left: Salix x 'Flame, S. 'Americana', S. integra 'Hakuro Nishiki', and S. x acutifolia) free from shoots on the "trunk" is fairly easy as you basically just rub your hand down the trunk while the shoots are small. As you may see on the photos, the different varieties have different habits as to how many shoots they grow and how easily they are pinched off.
The Harlequin tree takes much more work and the variety in the picture, S. koriyanagi 'Rubykins' will have a lot of shoots in the spring and early summer with fewer shoots continuing to show up during the rest of the growing season and the following years.

In the photo to the left I have removed all the shoots and the trunks look clean and smooth.
When pinching off the shoots it is important to be careful not to damage the bark on the tree. If the shoot has been left too long you may rip some of the bark off if you "rub" or pull on the shoot - risking that that particular willow rod will die. If the shoots have been allowed to grow too big, it is a good idea to pinch them off with your finger tips or cut them off with a small pruning tool.

As the plants grow, you will also like to encourage the crowns to "fill in", get bigger and fuller. This is accomplished by pruning the crown a few times during the summer - starting when the individual shoots in the crown are about 25 cm long, cutting off about 10 cm.

On the left are the trees before pruning - I was late with the first pruning this summer - and on the right the same tree after it has been pruned.
The top tree is S. x acutifolia

The bottom tree is S. koriyanagi 'Rubykins'

They look a little "stunted" right after this operation, but the plants respond by developing two or more new shoots for each tip that has been cut off and after a few weeks you will have a larger, bushier crown.

This is what my very first Harlequin tree looks like now, planted in the garden.