Over 20 years ago I broke my own heart with the most painful learning experience of my life. I’d used the excess small fieldstone off my property to create a rock mulch around the base of my large wisteria. It would keep water in the root zone from surface evaporation during the heat of summer. I didn’t use a liner underneath and just placed the cupcake-sized stones into a tidy layer.
A year or two later, the wisteria was even bigger and weather prevented me from late fall leaf chores. The wisteria lost its leaves like it always does and they accumulated on top of the rocks around the base of the plant. Winds drove the leaves up against the trunk higher than they’d be when decomposing on the soil surface. Without contact with soil microbes that decomposed prior year’s leaves, the rock allowed them to build up enough to cause problems.
The following spring it happened while in full lavender-flowered glory. The whole vine that covered half the garage just drooped and died. I knew by the look that it was a systemic problem, not something out in the air like bugs and diseases. Going to the base of the trunk where above and below ground parts meet up, I knew quickly this was crown rot. I tested with my fingernail by nicking the darkened bark. If healthy, it should be hard to nick and green underneath. If it nicks really easily and is tan or brown underneath, the cambium is dead and it’s crown rot.
The trunk base about the diameter of my calf had been fully encased in moldy saturated leaves that cut off oxygen to the bark. Because bark needs to breathe, this caused it to die along with the inner cambium layer just underneath it. This interference with the root to stem contact is the death knell for trees and other woody plants.
The wisteria I’d nursed from a one gallon stick would not leaf out again nor bloom that year because its vascular system had been cut off. Only the roots remain alive and may resprout stems and begin again after shock recovery period passes.
Don’t underestimate these stumps because they are huge root systems that are capable of driving very fast regeneration called “adventitious growth.” If such a thing happened to trees on old farms, they’d have a new branch grafted on to the stump to speed regeneration or perhaps change the variety to boot.
Be cognizant of crown rot when planting trees and shrubs in the fall, and here’s why. For many years I worked as follow-up on newly installed landscapes during the company’s 30-day maintenance period. I encountered the same problem over and over caused by container grown trees planted too deeply. Sometimes it was caused by an under rootball pocket that never settled when it was watered in. Under irrigation it settles later when we’re not paying attention and crown rot begins.
Such conditions can be avoided when addressed quickly, but if you don’t check, you’ll chance losing it to a dozen other crown rot scenarios. Don’t overlook your older ones, either, because like my wisteria, it’s even more painful when you lose them because they’re impossible to replace.
With everyone mulching everything these days due to drought, there’s no doubt this problem will arise with rains. Mulches themselves are a major cause of crown rot if not kept clear of the trunk. I prefer a 6-inch collar of exposed ground round the base of all plants.
The relationship between mulching and crown rot is undeniable. So take a day and check closely to make sure every tree, shrub and vine has enough clearance today and tomorrow so a few leaves won’t kill it before spring.
Maureen Gilmer is an author, horticulturist and landscape designer. Learn more at www.MoPlants.com. Contact her at firstname.lastname@example.org or P.O. Box 891, Morongo Valley, CA 92256.