The Garden Professors

A community of learners: Berkshire Botanical Garden’s Horticulture Certificate Program provides classes and hands-on workshops taught by some of the region’s top experts in gardening, horticulture and the environment.


By Thomas Christopher


My first gardening teacher was my mother – she had learned the basics of the craft from her mother and through a lifetime of experience. Later, in the mid 1970’s, I supplemented what she had taught me with a two-year apprenticeship at the New York Botanical Garden. There I had the chance to work with some superb craftsmen and women; again, they mostly taught me what their mentors had taught them. I also took classes while enrolled in the New York Botanical Garden Student Horticulturist Program, and there I learned some of the science related to plant care, but not too much.  Gardening was just beginning to be put on a scientific basis back then and much of the practices of good gardeners were based on either inherited experience or hands-on experience.

I would never dismiss this sort of learning, but it did have its limitations.  Sometimes the supposed evidence for what we did was just hearsay: someone told us that a particular practice was correct, and if we respected the source, we tended to accept what they told us. Often, our only justification for what we did was that it seemed plausible. For example, as a student I was taught that when planting a balled and burlapped tree or shrub, I should never disturb or in any way damage the root ball, the mass of soil and roots inside the burlap. Supposedly, damaging this in any way would severely damage or kill the plant.

Recently, however, I have learned that this is exactly wrong. Research by a horticultural professor at Washington State University, Dr. Linda Chalker-Scott, proved that leaving the rootball undisturbed reduces the incentive for the newly planted tree or shrub to send roots into the surrounding soil. Typically, the undisturbed roots never outgrow the lump of soil in which they were raised. This means that the plant will be poorly anchored as it grows bigger, easily pushed over by the wind.  Likewise, because its roots don’t extend into the surrounding soil, such a tree or shrub is very susceptible to drought.

Through experimentation and observation, Dr. Chalker-Scott has proven that the most effective way to transplant a tree or shrub, whether balled and burlapped or grown in a container, is to first soak the rootball in a tub of water, and then carefully tease the soil off the outer roots. If these roots have grown in a circle around the exterior of the rootball, as they often do, they must be pruned back or pulled out straight. When the tree or shrub is placed in the planting hole, the freshly exposed roots should be arranged so that they reach outward like the spokes on a wheel. Then the hole is backfilled with the native soil. Large rocks may be removed but nothing, not compost or peat or manure, is mixed with the soil before it is returned to the soil and carefully packed in around the roots.

This is not all I have learned from Dr. Chalker-Scott. She teaches a fundamentally different attitude toward gardening. While she doesn’t dismiss the knowledge to be gained from traditional practices, she insists that it must be verified by science. To help gardeners with this process, she has joined with several colleagues to form an online group that calls itself “The Garden Professors.” The Garden Professors maintain an online blog – – where they write about horticultural topics from a science-based perspective. Did you know that among the drawbacks of using cardboard as a mulch is that it attracts termites? Do you know what the recommended interval is between applying uncomposted manures to the garden and the harvesting of leafy greens (120 days) or tomatoes and other drops that do not contact the soil (90 days)?

A gardener with a specific question can turn to The Garden Professors blog Facebook page.  After familiarizing themselves with the rules of this group and joining, gardeners can pose questions.  Administrators of the blog and other members are then invited to post science-based answers. Home remedies are not allowed, nor are non-science-based answers or links to non-science-based websites. Those seeking plant or insect i.d.’s should go elsewhere – the blog lists a number of relevant resources.  The administrators will close comments on a question when the subject is judged to be exhausted, although they may re-open it if new research emerges.

This sort of rigor isn’t for everyone.  It can be upsetting to find long-held beliefs challenged.  I find it bracing.

  Thomas Christopher is the co-author of “Garden Revolution” (Timber Press, 2016) and is a volunteer at Berkshire Botanical Garden. Be-a-Better-Gardener is a community service of Berkshire Botanical Garden, one of the nation’s oldest botanical gardens in Stockbridge, MA. Its mission to provide knowledge of gardening and the environment through 25 display gardens and a diverse range of classes informs and inspires thousands of students and visitors on horticultural topics every year.  Thomas Christopher is the co-author of Garden Revolution (Timber press, 2016) and is a volunteer at Berkshire Botanical Garden.