As the garden world turns
What gardeners used to do and think—and what we know now
Mulch around trees should be spread over the root area, not heaped up against the trunk. No mulch “volcanoes,” please!
It’s good to learn how to garden the old-fashioned way, with knowledge passed down through generations—mostly. But much has changed in the gardening world in the past decades. Horticulture science, the landscaping profession, and the entire “green industry”—from hybridizers to growers to marketers—have evolved and that evolution should influence what gardeners do on their properties, regardless of long-held traditions.
Science now says: no more compartmentalization
Many people today remember learning to cut off a broken tree limb flush with the trunk, in a straight line. Others just cut tree limbs off wherever the branches stick out too far. Or they leave a broken branch stub where it broke, thinking that trees can fix themselves. These are all wrong choices.
In the 1970s, scientist Alex Shigo discovered and explained that trees handle wounds using a process called compartmentalization. It changed forever how arborists and homeowners should prune tree limbs. The process, known as CODIT (Compartmentalization of Disease in Trees) works like this: when a tree is wounded, certain cells are spurred into action to form a series of walls around the wound. Different kinds of cells plug tissues, produce anti-fungal substances, and form barriers so that fungal or bacterial infections can’t penetrate the tree beyond that wound site. Simply put, the process seals off the wound.
Wrong: Cutting the limb flush with the trunk, or cutting a limb in the middle (leaving a stub) prevents an effective sealing off process. Decay will proceed from the wound through the whole plant.
Right: If a tree is pruned just outside the branch bark collar or branch bark ridge (the thick part where a branch meets the trunk), the right cells are in the right place to begin the compartmentalization process.
Science now says: soil is alive!
Former soil textbooks focused on the mineral components of soil and the differences between sandy, loamy, clay, and various soil combinations. Farmers and gardeners knew about adding organic matter—called humus in old textbooks—to improve soil texture, and appreciated the aeration and decomposition that earthworms achieved. But soil teachers weren’t talking about microorganisms, or mycorrhizae very much until (maybe) the 1980s, depending upon where the learning was taking place.
Today, most gardeners have probably heard something about life in the soil—both macroorganisms (visible creatures such as worms, beetles, and centipedes) and microorganisms (invisible living things including bacteria, actinomycetes, fungi, algae, and others). In gardening classes, students now learn to add compost and other forms of organic matter to improve soil texture and to feed and stimulate soil organisms so that they can provide nutrition for plants. This concept of soil life has changed how we treat our soil.
Wrong: Compacting soil by parking on it or walking on it when it’s wet is destructive of texture and soil life; the organisms need air and moisture as well as organic matter. Tilling soil until it is powdery is equally destructive. Many chemical fertilizers disrupt the community of organisms in soil, as well.
Right: Since the soil is alive, stimulate and increase that life by “feeding” it with compost and other organic matter such as manures and chopped leaves. Make or purchase compost with an awareness that all composts aren’t equal; some have different communities of microorganisms. (This is an intense learning area for everyone, including compost experts and makers.)
Science now says: the roots are not where you think they are
If you remember seeing Presidents Kennedy and Nixon on a TV with rabbit ears, you probably also remember your schoolteacher showing an illustration of a tree with a round top and an equally round root structure below the soil line. That was the belief, including the idea that most trees had “tap roots” that grew straight down.
Along came Cornell University’s Urban Horticulture Institute, under the leadership of Nina Bassuk, which produced prolific research about arboriculture, site analysis, and management. The breakthroughs included that tree roots are mostly in the top twenty inches of soil and that sixty percent of them reach beyond the tips of the farthest branches of a mature tree. Bassuk and her colleagues lectured adamantly to the landscape and nursery professionals, as well as to extension folks, that the terrible practice of “volcano mulching” (mounding compost against tree trunks) must be ended.
Wrong: People dug “hundred dollar holes for ten dollar trees,” and the holes were very deep. (Sadly, this still happens.) Utility trenches were dug and construction work was done close to trees, even within the dripline, cutting off half of a mature tree’s roots. Workers still tell homeowners, “Oh, it’s all right, lady; those tree roots are way under where we are digging.” And volcano mulching is still seen.
Right: A tree should be planted with the root flare (where the trunk swoops outward into the root system) above ground, not buried in the soil. You should see that flare at the bottom of all trees. The hole should be more than three times the width of the root ball and backfilled with the same soil those roots will have to grow in. (In the case of depleted or heavy soil, the backfill can be amended with compost.) The hole should be about the depth of the root ball (not the very deep hole that was recommended in old books) so the tree doesn’t sink into a clay basin. And perhaps three inches of mulch should be spread over the root area, not touching the trunk!
Japanese knotweed (left) and barberry used to be OK to plant. We know better now.
The changing grasp of green issues
There are broad changes in public awareness and acceptance of several gardening, landscaping, and ecological concepts. The following observations are based on thirty years of learning, teaching, and writing for Master Gardeners, the gardening public, and landscape professionals, especially on organic gardening and ecology topics.
On organic gardening and pesticides:
Observations that pesticides kill beneficial insects are no longer met with eye-rolling in professional circles. Rodale Books, Organic Gardener Magazine, Mother Earth News, NOFA (Northeast Organic Farming Association), university research, and medical science have won—at least to the extent that a large percentage of gardeners want organic products. Some of the nongardening public appear to be oblivious about synthetic pest control and fertilizer products, but the conversation is out there. Most gardening audiences say they strongly prefer to avoid pesticides, and younger gardeners are adamant about not using pesticides. They want to garden organically. CNLPs (certified nursery and landscaping professionals) and others in the industry practice IPM (Integrated Pest Management) and many landscape and lawn care companies offer organic programs in response to public demand.
On invasive species:
A century ago, it was common to hear that gardeners brought “Pretty! Interesting!” plants from other countries. Now some of those plants have destroyed habitats and farmlands and cost millions or billions of dollars for eradication. As recently as sixty years ago, USDA conservation and agriculture programs recommended using Japanese knotweed to control erosion, and multiflora rose for borders around country properties. (They’re sorry now!) Invasive plants still enter through shipping and other means. USDA and other scientists now understand the destructive nature of many non-native invasive species.
As for the public, now a large percentage of people “get it”—at least about kudzu, Japanese knotweed, common reed grass, purple loosestrife, and their ilk. Recent labeling of Japanese barberry and burning bush as invasive species have surprised many, even though New York State followed slowly behind most northeast states in that labeling. Scientists’ findings and ensuing legislation aren’t always agreed upon by affected industries or the general public.
On native plants, disappearing habitat, endangered species:
Most people are attuned to the severity of habitat destruction and its implications. Cornell’s Native Plant Conference is largely attended these days, though the majority are those who already get the concepts. In the 1980s, many gardeners had a vague idea that some native plants grew best where they “belonged,” but equally as many commented that those plants were unkempt and messy. Subsequently, birders and butterfly lovers led the charge to plant berrying and nectar-producing native plants. The industry learned to market some native plants (American Beauties is one example). Douglas Tallamy’s book, Bringing Nature Home, was a game-changer; it explains that native insects must have native plants so that entire ecosystem constructs can survive. And this planting must be done in cities and suburbs, as that is most of the habitat that is left.
On climate change:
Broad science-based knowledge, agreed upon by most science bodies around the world, has reached the educated public, although some people still seem to think it’s all about politics. Please see “The Plant Lady and the Birdwatcher Talk about Climate Change,” by Sally Cunningham and Gerry Rising (Buffalo Spree, September, 2017).
Through land-grant colleges such as Cornell and Penn State, and through scientists in arboriculture and all branches of the green industry, gardeners, landscapers, and the public have learned so much in just a couple of decades. There is more to study and to do, as the intensity of challenges to the natural environment increases.
Let the learning continue.