Plant’s growth habit provides function and beauty

MACOMB, Ill. — From a horticultural perspective, the term “habit” is not what you think.

There are certainly bad habits in gardening, like not cleaning soil off tools or buying plants with no feasible location to plant them. When you hear a horticulturist say the term “habit,” what that person is referring to is the form or shape a plant takes.

For instance, when the growth habit of a tree is described, there are terms you may recognize such as rounded, pyramidal, irregular and vase-shaped. One growth habit term that often is mispronounced is “fastigiate.” For some reason, the brain wants to say fast-ee-gate where in reality it is pronounced fas-tij-ee-it. Now that we all know how to say it, what does it mean? Fastigiate is a $20 word for “columnar.” 

Habit is primarily determined by genetics. There is more consideration for growth habit than most people realize when it comes to plant breeding. From a green industry perspective, yes, flowers sell, but a plant that flops over because its flowers are too heavy can lead to a disappointed customer. For example, many hydrangea breeders are pursuing dinnerplate-sized flowers that require an upright growth habit strong enough to support the weight of these massive blooms. At plant breeding presentations, some absolutely beautiful hydrangea flowers showcase dazzling colors. However, because the stem can’t support the weight, that unnamed hydrangea ends up in a literal compost heap never to be seen again.

Plant breeding is cut-throat. 

A plant’s growth habit certainly has a functional component. Whether you are growing a sturdy hydrangea or a street tree that can create a canopy without getting in the way. A vase-shaped habit for street trees is ideal as they have few lower branches, but higher branches that arch outwards creating a canopy overhead. This is what made the American elm an ideal street tree with its vase-shaped habit. Once we lost our elms, tree growers have worked for decades to fill the void left by Dutch elm disease. 

Aside from function, a plant’s growth habit has aesthetic appeal. In the mind of Americans, a street lined with vase-shaped trees is more comforting. One of the best times to observe a plant’s habit is in the winter. Readers should observe the branching habit of various deciduous trees and shrubs this winter. Some plants provide excellent winter interest based on their habit. 

Witch hazel (Hamamelis spp.) comes to mind as a tree that can have various habits depending on what cultivar is selected and where it is planted. Witch hazel is a small understory tree that has a smooth bark that stands out on a snow-covered landscape. Many witch hazels have a vase-shaped habit, but a witch hazel growing in Southern Illinois had an incredibly irregular and gnarly form. It looked like some type of haunted tree growing beneath the oaks. This goes to show how the growing location can also play a role in a plant’s habit.