Mulch Too Deep Can Lead to Collar Rot

Q. I've had a problem with a cape honeysuckle. I have two plants that are trellised and were thriving (~5 feet tall) until one of them began to wilt last Tuesday. By Saturday the leaves had all dried up and fallen off. I'm pretty sure it's a goner. There was no sign of insect or wind damage, and it had plenty of water. And the other plant is still doing fine. They had the same water schedule, same sun, same soil.

Crown rot or collar rot of honeysuckle after mulch has been removed from the stem. Notice the dark color like a watermark on the stem.

The only thing different with the dead plant was that I covered that side of the yard with a large 2-3" decorative redwood mulch two weeks ago. Could something leeching out of the mulch kill my honeysuckle? There's a red discoloration around the base of the stem (see attached picture), that makes me suspect this.

I'd like to get to the bottom of what happened before I invest in a replacement, especially given how quickly the plant died.

A. This sudden death sounds more like a problem of having wet mulch in contact with the stems. Wood mulches are great and have a lot of potential benefit to plants particularly honeysuckle. 

But, if the mulch is placed around the plant, and the plant is fairly young, and the mulch stays wet, it can cause the trunk of many plants to become infected with one of the soil borne diseases. This will rot the trunk of these plants and basically strangle the plant of water. We sometimes refer to this as collar or crown rot and it happens a lot with woody plants. 

We usually see this most often when woody plants are planted too deep in their planting hole and soil is in contact with the trunk. This is the reason plants must be planted at the correct depth. I have seen this also when established woody plants have soil mounded up around the trunk. When the soil stays wet, the trunk rots. We see it also with woody mulches in fruit trees. 

When woody mulches are in contact with the trunk of young trees the trees may develop collar or crown rot. We need to keep mulch away from the trunks of woody plants at least six inches to prevent this from happening. Use less wood mulch in the areas close to their trunks.Viragrow Delivers!