Here's an article I just wrote for City Trees magazine on root pruning. I tend to take an aggressive approach toward removing defective roots; better than removal and replanting in all but the most horrible cases.
I jsut spent 3 hrs today on a campus where parents pay $15k/yr for middle school. 90% of the installed trees had serious girdling root problems.
AS THE ROOT IS BENT, SO THE TREE WILL GROW
The Acer rubrum, red maple in front of the Forestry building did not look quite right. The eastern side of the crown was sparse, and shed its leaves early. The students in the Urban Forestry class had a variety of opinions—sunlight, pavement, pollution—but one looked to the bottom of the tree and came up with the right answer.
The tree was afflicted with a disorder that has reached epidemic proportions on installed trees in the urban landscape: deformed roots. The trunk flare and primary roots were covered in the nursery, sending lateral roots growing up and toward the trunk in search of oxygen and nutrients. After a few years of this misgrowth, the tree was dug up, placed in a wire basket and sold. Despite its prominent location in front of a land-grant university’s forestry school, the installers treated it like any other tree; burying it deep, leaving the wire basket on, and piling on extra soil and mulch.
The largest girdling root was squeezing the top of the primary root growing to the east, following a typical pattern: under the most deformed section of the crown is the most seriously squeezed buttress root . Where the root cut at harvest time met the wire basket (marked by the top orange flagging), it formed a “knuckle” of tissue, from which lateral roots grew in many directions. There was no radial (outward) growth straight out from the point of contact with the wire. Deformities due to wire basket damage aside, this article is about pruning defective roots.
First comes the RCE (Root Collar Examination), when the soil is cleared away so the sides of the primary roots are exposed. Smaller roots growing upward and inward must be snipped out of the way to find the flare. Soil is then cleared away from the girdling roots as much as is practical. The idea is to make the cuts a good distance away, so their regrowth does not regirdle the trunk or buttress root. Simple tools were used on this maple: loppers for bigger roots and hand pruners for smaller roots. Clean cuts are made, preferably at laterals growing in a desired direction. Sealants are not typically recommended.
Next we’ll look at an Acer palmatum, Japanese maple. It was planted in a lawn, above grade and volcano-mulched. The RCE first revealed a pencil-sized root girdling the trunk. It was removed with a hand pruner, but given the track record of Japanese maples coming out of nurseries, we decided to follow the primary roots as they grew away from the trunk. This revealed a large girdling root, which required a hand saw to sever it back to a lateral root growing in a radial direction. Finally, the upper loops of the wire basket were cut where they were in a position to damage the roots.
The biggest tree we saved for last: one of a pair of Magnolia grandiflora planted sixty years ago (previously featured in the April 2005 Dendro Detective column in Arborist News). Its twin grew a full crown, but this one started dying back on one side. The twin had beautifully-shaped buttresses, but the declining tree had only a little flare showing. Small roots lapping over buttress roots above the soil surface were dealt with by loppers.
An RCE found that the trunk on the deformed tree was strongly girdled by its own roots. Again, the girdling was worst on the affected side of the trunk. Some books such as A New Tree Biology say that you can do more harm than good by removing big girdling roots. The tree needs roots for uptake, and it's hard not to wound the trunk while removing them, so they say it's best not to disturb them. First do no harm, as Hippocrates said. But letting this magnolia slowly strangle itself was not an option.
Following accepted guidelines for branch pruning, I decided to limit the amount of roots removed to under 20% per dose. First I used a chainsaw, to make “plunge cuts” on embedded roots. With handsaw, hand pruners and finally with hammer and chisel I sliced out three root sections. I somehow managed to avoid gouging the trunk, and fortunately the bark on the roots was not stuck to the bark on the trunk, but came off cleanly with a "pop”. The plan is to return annually until the trunk is free of any root that girdles more than 10% of the circumference.
On all trees that are root-pruned, the soil around the dripline should be aerated, inoculated, fertilized and mulched, to stimulate root function that can replace what had to be cut away. A miner’s pick is an excellent tool for aeration, because unlike an auger it fractures the soil instead of glazing it, and damages a few roots instead of chewing up several roots. The debris excavated during an RCE—aged mulch, nursery soil and roots-- is blended and stuffed into these holes, inoculating the soil with freshly harvested mycorrhizae.
The trunk flare is often buried early in the growing process, and buried deeper at planting time. Some specifications still instruct the landscape contractors to plant not the trunk flare but the rootball at ground level. This they dutifully do, then toss on several inches of extra mulch. From the grower to the plant buyer to the spec writer to the landscape designer to the final customer, few people stop to say, “I want to see the trunk flare”.
An ounce of prevention in the nursery, or four ounces of inspection at buying time, or eight ounces of correction at planting time can prevent a ton of attempted cure after the problems start to show. Good roots grow good trees. Simple, isn’t it?
