A Witch's Broom for Christmas

by Gregory Quinn

They form on Christmas trees, long after Hallowe'en has past.

While selling Christmas trees last December, I had an opportunity to appreciate one of nature's anomalies: the witch's broom. These are deformities in woody plants, caused by a hormonal imbalance, which is in turn caused by disease, infestation, over-use of herbicides, or genetic mutation. Parasites slow down growth, triggering dormant buds to open and grow. Many buds grow simultaneously, giving a bushy appearance. What causes the broom usually contributes to the death of the plant.

It is partly because of our expectations of what a Christmas tree should look like that they form. In order to achieve the 'christmas tree' shape, the trees are pruned twice a year by machete. If pruned incorrectly, disease can easily enter. It is funny that we want a densely foliaged, full, and artificial shape in a live tree, which means heavy pruning, that results in these deformities.

Over and over this summer I heard the request for a 'christmas tree', the seeker not knowing that, like bonsai, this shape is the product of years of careful, or not so careful, pruning. I have heard tell of many injuries on workers navigating uneven ground while swinging the machete. The trees also received such injuries.

The brooms are easily identified during winter on deciduous trees, but on evergreens you must look inside to find their matted, twisted, growths. Horror, repugnance, or at least fascination was on the face of all who discovered them. With their fine twiggy ramification, they look a bit like half-developed bonsai. In fact, these brooms have been used for developing many dwarf plants. Jean Iseli, the conifer virtuoso, discovered a witch's broom on his dwarf Alberta spruce, Picea glauca 'Conica'. This became the miniature Picea glauca 'Jean's Dilly', with smaller, finer needles and slower, more compact growth.

The one very useful aspect of these growths is that they form natural bird's nests, and thereby provide shelter for beneficial creatures. Unfortunately, while birds control insect and rodent populations, they also may spread mistletoe, one of the parasites that cause witch's broom.

We need to look everywhere for inspiration in creating natural forms in bonsai, even to these mysterious contorted shapes. Perhaps we could also learn how to trigger back budding using plant hormones ourselves, to further the development of our trees. Don't be scared by the witch's broom!