Cultivate'26 session preview: Weed Management for Container-Grown Hydrangea

Nursery Management: Why is this a valuable session for hydrangea growers to attend?

Anthony Witcher: There’s only a handful of herbicide products that are labeled for use on hydrangea. And sometimes labeling is pretty vague. You’ve got a few products labeled for Hydrangea macrophylla, one product labeled for oakleaf hydrangea, and then a couple that are just labeled for Hydrangea spp., which obviously isn’t very helpful when you’ve got four different species that you’re growing. Then you’ve got all the cultivars out there, and so there’s not a lot of information on what’s safe to put on hydrangeas.

NM: Why is weed management such a challenge for container production of Hydrangea?

AW: While many growers rely on pre-emergent herbicides for other deciduous shrubs, hydrangea is highly sensitive to numerous active ingredients, and only a limited number of products are currently labeled for safe use. As a result, producers often fall back on manual hand weeding, which is both labor intensive and costly.

NM: What research findings will you cover in your session?

AW: Our first trial focused on eight different granular herbicides, because that’s what’s going to be safest in containers and over the top of these plants. We tested them on all four species and also two cultivars of each species, because there can be some variability even within one species of whether one cultivar may be tolerant, another may be damaged by a certain herbicide.

We were trying to narrow down which products may be troublesome in certain species. We were also trying to find out if we can have one product that’s labeled for one species, why can’t we use it on the other species?

NM: What can attendees expect to learn from your talk?

AW: I’ll discuss a list of some of the products that may be safe on hydrangeas that beforehand people haven’t used just because they weren’t labeled. We’ll identify some products that may be safe for hydrangeas and also look at one technique in particular with which you can limit the amount of damage potentially from the herbicide. We have some data that may be helpful.

A lot of growers are using rice hulls as a mulch as a non-chemical alternative for weed control. I’ll go over some different mulches that we’ve trialed the last few years and how effective they are on weed control.

Attendees will take away some products they potentially could use on hydrangeas and also some alternative methods for controlling weeds in hydrangeas. They will gain practical insights to evaluate and select herbicides that support weed suppression without injuring plants.