Tried and failed to kill hydrangea macrophylla

[Rivera]

When my wife and I bought our house a few years ago, there was a very old hydrangea macrophylla, about 7' tall and 8' wide in a moderately shady north-facing part of the yard. The plant appeared senescent, largely defoliated, and suffering from a possible complex of fungal infestations (most noticeably powdery mildew). There was an active hummingbird nest in it, so I left it alone.

When the birds vacated, I unsuccessfully attempted to control the fungus and revive the plant. Feeling I'd made an effort and not really wanting the plant anyway, I cut it to the ground. I dug about a foot down around the gnarly taproot (about 4" thick) and cut out several large sections of the woody roots with a reciprocating saw.

Since the plant already seemed old and weak, I thought that would do it and in short time I began planting around it. Well, you know where this is going. Some time after the surrounding plants had grown in a bit, I noticed the hydrangea growing many new shoots from the scattered remnants of its root system a few inches beneath the soil.

I remembered a friend saying something about planning to kill a tree by driving some kind of large copper fastener into it and leaving it there till the tree died. I don't know if he actually did this, but I didn't have any other ideas so I ground the end of some 3/4" copper pipe to fashion it into a stake and drove that stake about 6" into the most robust part of the root mass that I could find, splitting that root mass in the process.

Well, it's still alive, and still sending up healthy young leaves. I've nipped off all new growth many times, hoping that would demoralize it into accepting its fate, but all to no avail.

Hydrangea: 1

Me: 0

[Merlyn]

You could try what I do on stubborn vines.  I chop them back to the ground, then wait a week or two for them to resprout.  Instead of cutting the new growth I hit every leaf with Roundup/Glyphosate mixed on the "brush killer" dosage with a few drops of Dawn soap mixed in.  The soap helps break down the waxy leaf coating so it absorbs completely.  This is about 50% effective on vines, and might work on your Hydrangea...

[Silas_Sancona]

13 hours ago, Rivera said:

When my wife and I bought our house a few years ago, there was a very old hydrangea macrophylla, about 7' tall and 8' wide in a moderately shady north-facing part of the yard. The plant appeared senescent, largely defoliated, and suffering from a possible complex of fungal infestations (most noticeably powdery mildew). There was an active hummingbird nest in it, so I left it alone.

When the birds vacated, I unsuccessfully attempted to control the fungus and revive the plant. Feeling I'd made an effort and not really wanting the plant anyway, I cut it to the ground. I dug about a foot down around the gnarly taproot (about 4" thick) and cut out several large sections of the woody roots with a reciprocating saw.

Since the plant already seemed old and weak, I thought that would do it and in short time I began planting around it. Well, you know where this is going. Some time after the surrounding plants had grown in a bit, I noticed the hydrangea growing many new shoots from the scattered remnants of its root system a few inches beneath the soil.

I remembered a friend saying something about planning to kill a tree by driving some kind of large copper fastener into it and leaving it there till the tree died. I don't know if he actually did this, but I didn't have any other ideas so I ground the end of some 3/4" copper pipe to fashion it into a stake and drove that stake about 6" into the most robust part of the root mass that I could find, splitting that root mass in the process.

Well, it's still alive, and still sending up healthy young leaves. I've nipped off all new growth many times, hoping that would demoralize it into accepting its fate, but all to no avail.

Hydrangea: 1

Me: 0

Yeah, lol when happy, they can be very stubborn to kill w/ out  digging up every piece you find sprouting.  Kind of like dealing w/ Bermuda Grass ( ..which is 10x's worse trying to control / fully eradicate )

Never heard about the Copper fastener idea and not certain it actually works ..Same realm as other  "Grandpa - era gardening advise" ideas as the " Putting nails around X plants to provide Copper "  Which definitely doesn't work. 

Maybe if you keep cutting off any top growth the roots will eventually exhaust what energy they have stored for generating growth..  Then again, maybe not..

[Darold Petty]

I would use Glyphosate, and a heavy application.

[Rivera]

2 hours ago, Silas_Sancona said:

Then again, maybe not..

😂 ...that's my fear!

Much thanks to all for weighing in. The irony is, if this hydrangea had demonstrated such youthful vigor before I cut it down, I would've just let it stay! 

This is what I get for taking a half measure. I should've ground every bit of it up when I had the chance, but now I have to dance around the roots of the surrounding plants.

I'm willing to go to considerable effort to avoid the use of glyphosate. What can I say, I'm a stubborn MFer and I'm concerned about collateral damage. I will consider it as that's the advice I seem to be getting from people more experienced than myself.

I'm going to make another hearty effort to dig around in there and remove every bit I can find before I go that route.

[Silas_Sancona]

9 minutes ago, Rivera said:

😂 ...that's my fear!

Much thanks to all for weighing in. The irony is, if this hydrangea had demonstrated such youthful vigor before I cut it down, I would've just let it stay! 

This is what I get for taking a half measure. I should've ground every bit of it up when I had the chance, but now I have to dance around the roots of the surrounding plants.

I'm willing to go to considerable effort to avoid the use of glyphosate. What can I say, I'm a stubborn MFer and I'm concerned about collateral damage. I will consider it as that's the advice I seem to be getting from people more experienced than myself.

I'm going to make another hearty effort to dig around in there and remove every bit I can find before I go that route.

   I say the same thing every time i dig out random patches of Bermuda that pop up in non- lawn areas, lol..  Just when i think i got it out at root level ..it waves an ugly green finger at me through the soil a week or two later. 🤷‍♂️🤣

Only time i myself resort to chemical use is for something that i know pulling won't eradicate / will make worse.. Nutgrass invading -everything- in my case last year..  Other than that, "cancer causers / ecology killers" are banned from the yard.