If trees could talk, they’d probably start by saying, “Enough with the insults now.”
In more than 30 years of working with trees, Christopher Roddick has made it a practice to listen to their untold language – and show respect to some of the largest and oldest creatures among us.
Roddick is head arborist and grounds foreman at the Brooklyn Botanic Garden, a position he’s leaving this summer when he and his wife, Rebecca McMakin, director of horticulture at Brooklyn Bridge Park, move north. Her first stop: a fellowship she’s doing at Harvard University.
But Roddick won’t forget the trees in the botanical garden—old friends by now—and what they’ve taught him. Specifically about how we expect ignorant humans to adapt to our gardening and home improvement, not the other way around. Too often, we don’t take into account the needs of our trees.
“As an arborist, I usually don’t get calls unless a tree is in trouble,” he said. “And I ask, ‘Has anything changed around this?'”
At first, the answer is almost always no — and then it’s something like, “Well, we keep the patio nearby. But that was five years ago.”
“A tree can hold its breath for a few years, but then…” Roddick retorted, as if preferring not to remember all the bad consequences. “When you’re attacked, you defend yourself—but to a tree, that means you can’t get away.”
Trees have adapted, making compounds to help ward off herbicide and fungal infections. But no chemical is strong enough for what we ruin: We dig or drive in their root zone. We prune, not because a tree needs it, but because a garden bed underneath has become too shady for our liking. We trap a tree in a sea of lawns, where it is exposed to unwanted fertilizer and an automatic watering schedule.
“I’m not a big fan of planting a tree in the middle of the lawn,” Roddick said. “Most of the shade trees we use are forest species, and they often grow better in a group.”
Understory trees, for example, like flowering dogwood (Cornus florida), are not suitable for ripening in full sun.
Beyond Ornamental Gardening
The way Roddick sees trees has changed since he first studied ornamental gardening.
“I learned about trees from the point of view of choosing species because of their ornamentation – what is in it for us to see or eat,” he said.
But the appearance of a tree is not the whole story.
“When you look at a tree, you see only a part of it,” he said. “But a third to half of its mass is underground—the massive root system that is mostly in the top 18 inches of soil.” In compact urban soil, they can be in the top 6 inches.
Today, he is more in the mindset of ecological landscaping than ornamental gardening. He takes an ecosystem approach, recommending species that help create habitat.
He asks himself, “Can I use some of the insights I’ve seen in nature to tell about their use and care of trees?”
This may mean grouping several trees together, planted with native sedge (Carex). And perhaps leaving fallen trees to rot on the site. As they break down, these nurse logs, as they are called, add nutrients back to the soil and can support the next generation of seedling trees.
The way he thinks isn’t what most of us think, but trees might be happier if it were.
What Makes a Tree Resilient?
An important measure for Roddick: Not all species or individuals respond equally to changes. Similar actions by gardeners can trigger different effects depending on the type of tree, its life stage, and its overall health.
Trees with very heavy, woody root systems such as the white oak (Quercus alba) are not as resilient about disturbance as are fibrous-root species such as the dawn redwood (Metasequoia glyptostrobides).
“If I knew I was going to set up a garden, and I wanted a plant that was easy to work with, then Metasequoia is one I would feel very comfortable with,” he said. “I’m not going to be able to dig around trees like white oak. Especially as it ages, it handles turbulence much less.”
A fairly young tree with more resources may be more forgiving.
Species-specific differences in resilience are also visible where damage or disease occurs. Some trees are better able to compartmentalize – clipping off an injured or rotting section to protect the larger organism. Oaks are quite adept at this, Roddick said, which contributes to their generally long life spans.
At the other end are willow, cherry and magnolia, which are poor at compartmentalizing. As he put it, they’re “more live-fast-die-younger models.”
Shadow’s Reality (and the Gift)
Trees give shade. This is good news, especially in a warming world. But many gardeners balk when planning to grow plants like tomatoes or roses in the shade.
Roddick recalls a client who dreamed of a rose garden in his new home, where there was a mature sycamore maple (Acer pseudoplatanus).
“I suggested doing shade gardening instead of conserving the tree, but that was not to be the case,” he said. “People want more light for a lawn or garden, as opposed to designing around established shade trees.”
A common request: Couldn’t he put the tree up or open his canopy to let in more light? Their answer is always based on the species, its health and its age.
“It’s better to train a young tree to fit the garden, as opposed to trying to replace an older tree,” he said. “If we have to cut down part of an established tree to open it, does it have enough reserve resources to remain a healthy and safe tree?”
The client got his rose garden, but at the cost of the tree. It went into decline, became a security threat and eventually had to come down.
creating a living mulch layer
“Often the problem is “death by thousands of cuts,” said Roddick, when we garden too aggressively in the root zone—or worse, if an irrigation system is installed, through the tree’s lifeline. Repeatedly slicing.
He is a proponent of “living green mulch, not ring of bark mulch”. But turning an area under established woody plants into a ground-covering, herbaceous layer requires a gentle hand and patience.
“You need to start with smaller plants or divisions and dig very few holes,” he said.
Think a clay knife, not a shovel: With larger tools (or plants), the tree’s roots will be cut. “Nothing is a big deal,” he said. “But when you’re harboring a lot of roots, it can affect the tree.”
Another all-too-frequent insult: adding soil to tree roots to accommodate the plantings.
“Now the roots of the tree are buried, and they are not getting oxygen,” Roddick said. “How water moves through the root zone is about to change.”
Roots can begin to grow in new soil to find those resources, but if they dry out or become overwatered, it can cause a number of problems, including root-rot diseases.
Rarely does Roddick fertilize trees in his care.
In forest environments, nitrogen is not very abundant, he said, so trees don’t need much of it. Applying fertilizers high in nitrogen (even unintentionally, when feeding an adjacent lawn) can be costly to a tree. “You are not giving it food; The tree makes its own through photosynthesis,” he said.
“Nitrogen stimulates growth,” he said, but it means the tree “has to be pulled from its reserve and pay for that growth. You’re actually increasing its reserves by forcing it to grow artificially.” can reduce.”
The one exception is a tree grown in a large container, which you water too often, which drains the nutrients of the soil. But with trees growing in the ground, there’s a better way than applying fertilizer: Allow fallen leaves to remain in autumn so they can slowly return nutrients to the soil.
When Roddick lectures these days, he often ends with an eclectic message: “Plant trees, mostly natives—and save as many old ones as you can.”
The ones they recommend include citruswood (Oxydendrum arboreum), which is often propagated for its summer flowers and fall foliage, though they’ve got “its winter aesthetics, on the whole, hanging down seedpods.” ” This is a tree that he likes to see planted in a group.
In the original botanical garden of the Brooklyn Botanic Garden, he came to appreciate the showy bark of shade-adapted striped maple or moosewood (Acer pennsylvanicum).
The botanical garden also houses a redbud (Cercis canadensis) collection, and in front of their Brooklyn home, he and McMakin planted purple-leaved cultivar forest pansies for the hundreds of hearts hanging from their branches.
Fringetree (Chionanthus virginicus), good for small gardens, has fragrant white spring flowers and yellow color (as well as blue fruit on female plants). One downside: This emerald is susceptible to ash borer.
Pawpaw (Asimina triloba) has it all: flowers, fall color and fruit, with a custard texture and complex flavor.
And Roddick wouldn’t be without the fast-established sassafras (Sassafras albidum), which has distinctively shaped leaves that catch fire in autumn. Yes, management is needed to discourage colony formation.
But then, a full stand of Sassafras wouldn’t be so bad, he said: “I’ll spend my entire fall sitting there.”