How to Be a Better Plant Buyer
Surf the databases of the National Agricultural Statistics Service -- not exactly summer beach reading, I grant you -- and you might find something weird and wonderful.
Surely, not a lot of people know that in Tennessee, the value of greenhouse and nursery crops is outranked only by soybeans, broiler chickens and cattle? In Maryland, horticulture is a $1 billion-a-year industry. In Virginia, nursery crops top all others in cash value.
For a product that looms so large in our lives, it is quite remarkable how little we know about making good choices when we shop for plants for the garden.
Figuring out if a plant is healthy and well grown -- never mind if it is suited to its site or how large it will grow -- is a tricky endeavor. Shoppers do respond to plants that are large, bushy, green and vigorous, but those cues may not be enough to know that you're getting the best individual in a row of cloned trees.
To that end, we have put together an illustrated tutorial available online at washingtonpost.com on what to look for when you buy trees and shrubs at the nursery. This will help guide your woody plant buying in September and October, the optimum period for planting them as air temperatures cool but the soil remains warm for root growth.
Woody plants are usually sold balled and burlapped or in containers. Generally, larger trees are dug in the field and then wrapped in burlap, but the industry has moved toward raising more of its stock in containers, including larger trees. This shift has vastly widened the trade in plants since the 1970s because containerized plants can be shipped to market far more easily than those that are field-grown and then wrapped.
But if a tree or shrub is left too long in the pot, its roots can become congested to the point of harming the plant's long-term health.
"The roots of a containerized plant need to be developed to the point where they hold the soil but not to the point of excessive growth," said Warren Quinn, vice president for operations of the American Nursery and Landscape Association. This balance "is not completely definable or specific, but it's something a consumer, over time, can get a feel for." In other words, don't be shy about slipping a plant out of its pot to examine the roots.
Quinn edits the American Standard for Nursery Stock, a trade manual that establishes standards, specifications and guidelines for nursery plants as they make their way through an industry with a lot of middlemen and players. The holly you buy at the garden center may have been through three growers and two or three nurseries before it reaches you.
The manual is available online ( http:/
· For balled and burlapped shade trees, those with a trunk width of one inch should have a root ball that is 16 inches across. A 1.5-inch tree should have a root ball 20 inches across; a two-inch tree, 24 inches; and a three-inch tree, 32 inches. The same table also gives proper root-ball sizes for smaller ornamental trees such as dogwoods and redbuds.
· Woody plants that are not single-trunked present more of a challenge. For narrow or upright shrubs and for multi-stemmed trees, the manual recommends a root ball of 22 inches for a plant six feet high. An eight-foot plant should have a 28-inch ball.
· The depth of the root ball is also important and generally, for root balls smaller than 20 inches across, should be 65 percent of the diameter. For those above 20 inches, the ratio is 60 percent. Thus, a 16-inch root ball should have a depth of 10.5 inches. A root ball 28 inches wide should be 17 inches deep. The ball is measured from the point where the trunk flares into the roots.
· Another important feature is for the trunk to be at or close to the center of the root ball, so that the tree's roots are preserved as much as possible when it is dug.
· The recommended container sizes are more complicated to navigate in the manual, and they change based on the type of plant grown and also on its mature size. Suffice to say, there should be an obvious balance in the size of the plant and the container it is in.
· Beyond all these considerations, which have to do with the root health, I look for specimens with a pleasing and healthy branch structure, so that the tree can be trained when young to mature into something special. This often means looking for one whose trunk rises to a dominant leader. The online tutorial includes more advice about buying plants that are balled and burlapped vs. container grown, as well as tips on assessing the general health and structure of individual trees and shrubs.
Quinn concedes that it is not easy for a consumer without a horticultural background to divine all these aspects of plant buying. "It's tough. It's not the easiest product to purchase," he said. "Independent retailers can certainly do a good job of communicating value; they can buy high-quality stock and display it well and have knowledgeable employees. That's how good retailers sell plants."
But also carry this advice from Quinn next time you're shopping at the nursery: "The roots are everything."