Feeding and Protecting Trees in the Landscape
AS A LANDSCAPE CONTRACTOR, you know how to feed, water, trim and otherwise nurture the turf, shrubs and flowers on your clients’ properties. But when it comes to those big, tall, woody things in the middle of your clients’ turf areas, your confidence may wane.
We’re talking about trees, of course. Your clients may want, or expect, you to feed, water, trim and care for them, too. Trees, however, are “a whole ‘nother smoke,” as the old ads used to say. You may be hesitant to enter an arena you don’t feel comfortable in. On the other hand, there’s money to be made by taking care of trees.
It’s time for a fact-finding mission.
“The most important thing for a landscape caretaker to do is find out what the natural form is for those trees,” advises Dennis Swartzell, a board-certified master arborist and a principal in Las Vegas, Nevada-based Horticulture Consultants, Inc. “What’s their natural leaf color? Their natural leaf size? Once you know what the trees are supposed to look like, you can identify abnormalities much easier.”
“It’s really important for contractors to be knowledgeable about local tree species and what they’re prone to,” Swartzell says. “Knowing what types of problems may be persistent on particular trees is very helpful.”
What to feed them, and when
“Fertilizing trees is totally different than fertilizing turf or shrubs,” says Terrill Collier, board-certified master arborist and former owner of Collier Arbor Care in Clackamas, Oregon, (now a division of Stamford, Connecti cut-based Bartlett Tree Experts). He also has a BS in entomology. “Looking at how much growth was produced last year and the year before will give you a pretty good indicator of whether there’s a need for fertilization.”
The three major nutrients that all plants need are nitrogen, phosphorus and potassium. “Fertilizing trees with a 20-20-20 mix is a shotgun approach, and you’re probably wasting fertilizer,” says Collier. “For example, in the Pacific Northwest, we have soils that are naturally high in potassium. We don’t need to add more.”
“Fertilizing trees is not rocket science,” Swartzell said. “The primary thing to remember is that most urban trees will have a requirement for nitrogen to maintain growth. They don’t need a lot of phosphorus; they generally don’t need tons of potassium. In a desert region, there may be a requirement for micronutrients.”
Dr. Tom Smiley is an arboricultural researcher at Bartlett Tree Experts’ research lab in Charlotte, North Carolina. “The industry is going to a prescriptive fertilization program, where we sample the soil, the foliage, or both, to find out which nutrients are lacking, and how much we need to apply. Usually, we start with either a soil or foliar nutrient analysis to guide us in fertilizer selection and application amounts.”
Testing can be done with a kit, or sent out to a lab. “They’re fairly reasonable, and it’s another service you can provide for your customers. It demonstrates that you’re using a scientific, rather than a shotgun, approach.”
A tree’s own leaves can help keep it healthy. Instead of blowing them and bagging them, turn them into mulch. “Sanitizing the landscape of all that debris is bad,” says Collier. “It doesn’t emulate what a forest would do. Trees in a forest don’t need fertilizer. They have the forest floor, full of microorganisms that feed on the organic matter that drops, releasing those nu- trients to the trees.
Rather than rake them off the yard, I’d rake those leaves up around the tree.”
Perhaps the best way to deliver fertilizer is via injection, directly into a trees’ trunk or root crown. Getting nutrition into a tree by macro- or microinjection has several advantages. One, it’s a systemic approach; you’re putting nutrients right into the xylem of the tree, the part that conducts fluids up and throughout the organism.
Two, it’s very long-lasting. “A treatment of systemically applied fertilizer can last three to five years,” said Nate Dodds, president of Arcadia, California-based Mauget, Inc., the company that pioneered the trunk injection process.
Three, there’s no waste, as there can be with soil drenches or powdered chemicals. These can leach away or blow off; at any rate, not all of it will actually find its way into the tree. The excess also runs off into bodies of water, causing pollution.
Tree injection systems are easy to learn; you don’t need to be an arborist. The companies that make and distribute these products all have training programs, seminars, and webinars.
Learning to inject trees can give your business a real shot in the arm. “We’ve seen landscape contractors realize 60 to 70 percent gross profits by treating their customer’s trees,” said Rob Gorden, director of urban forestry and business development for Arborjet, Inc., Woburn, Massachusetts. “It’s a great service to add to your menu.”
Insects and diseases
Trees can’t tell us what’s eating them, and there are plenty of things out there that do. There are not only bugs with legs, but tiny bacteria and fungus spores that can make trees sick or kill them. These plagues often work hand in hand. An unhealthy tree is more prone to infection and invasion. Disease opens the door for bugs, and bugs open the door for diseases.
“In Southern California, we’re most concerned about the polyphagous shot borer (an invasive species from Asia),” says Smiley. “In this case, it’s not so much the beetle itself but the fungus it carries. Once that fungus gets inside a tree, it stops water movement inside its vascular system.” It’s said to be a threat to more than 200 different species of trees.
Again, trunk injection comes to the rescue. These products were designed to fight insects and disease. Studies have shown that they are more effective than soil drenches or sprays—the old way we used to deal with these things.
Those methods were reactive, done after the fact. It’s much better to head them off at the pass.
“But that’s not how we’re oriented, is it?” observes Dodds. “We don’t respond to something that isn’t in trouble yet. The owner of a tree may notice something chewing on it, but didn’t spot the eggs that came ahead of that. It’s only after there are swarms of insects on their trees that they’ll call out the pros.”
If a disease process has already started, can it be reversed with a shot? “Sometimes it can,” said Dodds. “When we can’t, we can stall it. The disease will eventually kill the tree, but we can slow things down to the point where you’ll have time to plant a replacement.”
What about an insect infestation that’s already reached critical mass? “We can therapeutically treat a tree for an active infestation of leaf-eating or sucking insects,” commented Dodds. “Generally, a tree responds with a new flush of growth. It may lose the leaves that were attacked, but it’ll put out new ones.”
In the past, most pest problems were fairly predictable. But that’s changed. “There’s been an invasion of a whole bunch of insects that don’t belong here,” said Gorden. “Gypsy moths, Japanese beetles, Emerald ash borers—and that’s just a few.”
Unfortunately, our trees have no natural defenses against these new invaders; that’s why, once here, they can wipe out whole forests. In the bugs’ home countries, the native trees aren’t injured much because of their evolved ability to identify and fight off the pests, or there are natural predators that keep the bugs in check.
Grass and trees go together like flowers and bees—right? Wrong. “Grass and trees really don’t compete well together,” said Jonathan Zundel, owner of Zundel Arboriculture, Expert Tree Care Company, Rockland, Idaho.
And yet, that’s what we find in most lawns. “You seldom find trees in nature with grass growing right up around their trunks,” says Collier. “That’s because they really don’t get along. It’s a cultural practice that we’ve developed, but it really causes trees to struggle.”
“The roots of grass go down several inches,” explains Zundel, “in the first few inches of soil, in the ‘rhizosphere.’ That’s also where the tree’s roots are, and where they gather a lot of their moisture. If you have both trees and grass competing for moisture, grass will win.”
He advises pulling the grass back and leaving a big circle, at least two feet wide, at the base of a tree. That circle should be filled with organic material, such as compost and wood chips. “The larger the grass and plant-free zone around the base of a tree, the better.”
This protects trees in other ways, too. “Novice landscape workers can hurt trees by simply not paying attention,” said Swartzell. “A lot of times, they let string trimmers or mowers hit the trunks. If you start knocking bark off, diseases and insects will get in there. This happens more than we care to admit in our industry.” It’s so common, in fact, that arborists have a name for it: ‘human blight.’ Another landscape practice arborists hate is ‘volcano mulching,’ piling mulch high around a tree’s trunk, sometimes as high as two feet. Instead, spread it around. “Bad things can happen with all that moisture being held right up against the trunk or the root crown,” said Collier.
“Always keep mulch six to 12 inches away from the trunk. Otherwise, the bark can rot, and that creates an area for pathogens, fungus, bacteria and insects to get in there,” said Collier. Root crowns also need light penetration. On certain trees, gas exchanges happen right through the root crown.
Southern Idaho, where Zundel works, is in a drought. But trees require water, lots of it. To keep them hydrated, he mulches with wood chips, “not chemically-filled wood chips, but the kind that tree services produce. Those have the ability to super-infuse themselves with water and then release it back into the soil.”
It’s easy to overlook subtle signs of stress. “You should be looking for leaves going ‘chlorotic,’ turning a yellowish color,” said Smiley. “That could be a sign of nutrient problems. Some pests will cause that as well. And spots on foliage can indicate disease.”
“Look for warning signs, like dead or thinning foliage, peeling bark or excessive branch dieback,” said Collier.
“Look for wounds where branches have fallen out. If a tree is going into decline, it may be due to root rot, or topping from 20 years ago. Check for cracks where long branches attach to the trunk. The branch might be starting to fall; that can be dangerous.”
In Las Vegas, ‘sun scald’ is a concern.
“Some tree species have thin bark, especially in their youth,” said Swartzell.
“It happens when a tree gets a lot of reflected heat, but it occurs in coldweather areas, too. If a tree is in dormancy, and it gets a real intense sunlight period, the bark can thaw out and refreeze, damaging it.”
“In our area, we have the flatheaded borer,” he continued. “Sun scald provides an entry point for that insect.”
In snowy areas, where de-icing salts are used, trees can get ‘salt burn.’ This salt buildup must be flushed out of root zones with copious amounts of water.
When to call an arborist
There are times when we’ve exceeded the limits of our knowledge.
Then it’s time to call in an expert. When should you call? When you’re in over your head, literally.
A certified arborist knows what to look for, and what it means. “I’ll visually examine a tree, look for decay, fungi, mushrooms or conks on the roots; that’s a sign of root rot,” said Smiley. “Most arborists can sound a tree with a mallet; if it’s very hollow, we can tell. If I need to look in-depth, I can drill into a trunk with small-diameter bits. There are specialized tools that send sound waves through a trunk and give me a 3-D picture of what’s going on inside.”
But you don’t have to become an arborist to take basic care of your clients’ trees. A little bit of knowledge will keep green on those branches, and in your wallet.