Every new year gives a gardener the chance for a new horticultural obsession. Ranging from irids and aroids to roses and beech cultivars, some new genus or plant type can cast a spell over the poor gardener. Often all it takes is a single purchase or the sighting of a new plant that intrigues us, and we are off into a fugue state. One friend succumbed to a spell that lasted for much longer that a year, and it is still almost unbearable to be in his company if the topic of Japanese chrysanthemums comes up. I have even considered serving him hemlock (the poisonous plant, not the conifer) when he goes on too long on the merits of some particular variety, but I tolerate him in the knowledge that any one of us could also be guilty of going on — and on — about our latest love.
So, here’s the story of my most recent trance state. This year, as I began to plant out an area in front of my house, I became obsessed by conifers in all forms, and that led me into the world of witch’s brooms, which now hold me in their thrall. A witch’s broom is a genetic aberration, and can be caused by a virus or fungus, or by an insect, or can simply be the result of a naturally occurring mutation. It shows up as a collection of congested twigs and branches, often set out on a limb, and it takes on the appearance of a twiggy broom held along the branch of a tree. Such growths are not uncommon on ashes, locusts and cherries, as well as on other deciduous trees. Some of them may be detrimental to the tree and should be removed. They also can signal that the tree is under stress, perhaps from a disease that may merit treatment. But others are harmless. A little online research or a call to an arborist can help determine if the broom should be removed or the plant treated. The broom itself can be easily removed by cutting with sterilized tools well back on the branch where the broom is located. The infected piece should then be discarded, not in one’s compost, but by removing it from the site completely.
But the witch’s brooms that have come to obsess me this year are those that are found on conifer species, particularly pines, firs and spruces. These forms, often the result of genetic mutation, are the source of many of the dwarf conifers available at nurseries. Dwarf conifers grow more slowly than the species from which they come and can take on different forms, often with the same congested branches as seen in the witch’s broom from which they have been grafted. These witch’s brooms are also known as sports. By taking cuttings of these sports and grafting them on to rootstock of the same species, horticulturists are able to take the traits of the sport and carry them forward onto a plant. Many of these plants will have smaller, more tightly branched growth, and some may even have a different needle color from that of their parent plant.
But do not let the word dwarf mislead you. While some of these plants grow more slowly than the species from which they sprang, as if a spell has been cast on them, they also can grow larger than the word dwarf implies. A dwarf of a concolor fir, for example, merely needs to grow more slowly than the species itself, and may top out shorter than the 50-foot height that the tree normally attains, but not necessarily by much. Some dwarfs grow mere inches a year, but still may attain a large size over time. As I am already in my fifties, I am not too concerned about their overwhelming my garden during my lifetime. Their genetic make-up also influences their form, which is often congested or contorted, sometimes yielding a weeping or tightly branched tree with a unique sculptural appearance.
At her garden at Rocky Hills, my friend Henriette had a collection of dwarf blue spruces that enchanted me from the moment I saw them. The fifteen-foot specimens were fifty years old and looked like modern works of art; they had taken on shapes that almost seemed to be formed through some ancient incantation, appearing completely other than the species from which they came. The blue spruces available now include many varieties that are the product of witch’s broom, including ‘Montgomery,’ a flat-topped form with congested branching. It reminds me of a bird’s nest, cast in silvery blue. A number of Japanese white pines with witch’s broom origins take on low-spreading and dense shapes. Yet another dwarf, the ‘Blue Star’ creeping juniper, propagated from a witch’s broom found on a upright juniper in a Dutch nursery, is commonly found in the trade and is used as a low spreading ground cover that has enraptured a large gardening audience.
The popularity of the ‘Blue Star’ juniper proves that I am not the only one susceptible to the spell of the witch’s broom. I just hope it does not get me pontificating, like my friend and his Japanese chrysanthemums. With that in mind, I will be careful not to accept any curative potions that may come my way until I am safely past this thrall.
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A gardener grows through observation, experimentation, and learning from the failures, triumphs, and hard work of oneself and others. In this sense, all gardeners are self-taught, while at the same time intrinsically connected to a tradition and a community that finds satisfaction through working the soil and sharing their experiences with one another. This column explores those relationships and how we learn about the world around us from plants and our fellow gardeners.
