When Bad Things Happen to Good Hydrangeas and How to Save Them

Happy Monday!

 Limelight Hydrangeas are just starting to bloom here in North Carolina,

the highlight of our mid-summer garden!

If you’re not familiar with Limelight Hydrangeas, they’re a panicle hydrangea

with an overall height and spread of 6 to 8 feet.

The large flower heads open as lime green in color, transitioning to creamy white

and grow 6 to 12 inches long!

Unlike other hydrangea varieties, they’re drought tolerant, thriving in full sun.

They bloom mid-summer, with the large white blooms offering an illusion of ‘cool’

in the garden on hot summer days and

when everything else is in the garden is looking tired and spent. . .

like I do in lugging my hose around in 90+ degree temps. ;)

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Like all panicle hydrangeas, Limelight Hydrangeas bloom on new wood.

Because of their size, they get a heavy pruning in winter or early spring,

cutting the canes back 3 – 4 feet.

Limelight Hydrangeas make ‘pitcher perfect’ blooms,

no flower arranging skills required,

just cut and place in the pitcher or vase of your choice.

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They make great dried flowers, acquiring a greenish hue,

then deepening to a burnished-bronze in late fall.

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We planted five Limelight Hydrangeas around The Potting Shed eight years ago.

I noticed last summer that one shrub in particular on the field side of my shed

was not as robust as the others, and the blooms looked stunted.

On a closer inspection, I discovered why. . .

 EEEEKKKK . . .cane borers!

‘Cane borer’ is a general term for a large variety of wood boring beetles,

that emerge from April to July, depending your gardening zone.

Some bore into the cane to lay eggs, while others bore in as larvae to feed.

I could never find a wood borer that that was specifically labeled ‘hydrangea cane borer,’

but after some googling and reading on NC State Extension’s website,

I learned there five groups of wood boring beetles

that infest trees and shrubs in North Carolina:

roundheaded wood borers, flatheaded wood borers, weevil grubs, ambrosia beetles and bark beetles;

the most common wood borers being the roundheaded and flatheaded variety.

Cane or wood borers lay eggs that bore into the end of branches of certain shrubs and trees.

Signs of cane borers are hollowed out branches, drooping and yellowing leaves,

stunted growth, and a sawdust-type material that results from boring.

As the larvae are inside the canes, insecticides are not an option to eradicate them.

The larvae grow by feeding on the pith of the stems and branches, causing stunted growth,

drooping and yellowing leaves, and ultimately death of the branches by

blocking xylem vessels and interfering with the transport of essential nutrients.

 Larvae can overwinter in the hollowed stems, emerging in the spring as adults.

As Limelight Hydrangeas bloom on new wood, there are an abundance of freshly cut wood stems

  providing borers easy access to fresh pith.

To save your hydrangeas and prevent further damage, cut the affected canes,

pruning back the branch until you see healthy wood.

It feels painful, especially when your hydrangea is just putting out new growth,

but necessary for the health of your shrub and future blooms.

Burn or bag your cut stems to get rid of any potential larvae to dispose of them;

don’t compost them.

Look at that poor damaged pith . . . :(

We cut the branches until we reached healthy wood, continuing to cut out the damaged pith

and cutting the shrub almost to the ground.

We sealed the freshly cut stems (details below on sealing)

along with few other affected stems found on neighboring hydrangeas.

With a little fertilizer and six weeks later, we had new healthy growth on the pruned hydrangea.

With some diligence and watching for signs for borers next spring,

we should have have healthy shrub and blooms again.

I noticed some evidence of cane borer damaged on some Endless Summer Hydrangeas nearby too.

I read online to seal your fresh cuts with wood glue as a deterrent to prevent beetles

boring into the freshly cut pith of the branches.

You’ll want to use a water resistant wood glue that

won’t wash away with the rain.

Apply the wood glue to your freshly cut branch on a day when rain showers aren’t imminent.

It will take the glue an hour or so to dry depending the heat and humidity.

I found it easier to apply by removing the cap and dipping a paint brush into the bottle,

rather than squeezing the glue directly from the bottle. 

Growth will emerge on the sides of the cut branch,

not top of the branch, so the glue won’t prohibit new growth.

Option 2: If you don’t have wood glue, use nail polish to seal your cut,

which is waterproof and will dry in 15 minutes on a hot day.

I picked up some neutral nail polish from Dollar Tree to blend with the wood stems.

It seems like a daunting task if you’re pruning hundreds of hydrangea canes,

but doable if you have just a few to seal as a preventive measure

to keep borers away from the tempting open wood of your stems.

I’m checking my hydrangeas daily for any news signs of borers.

Option 3: I just ordered some Pruning Sealer with Brush Top Applicator,

to have on hand, which should be a little less tedious to apply if the borers return.

Keep Calm and Garden On!

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 Between Naps on the Porch