Once upon a time, there was a girl shorter than a hydrangea bush who asked her uncle how he turned the pink flowers blue. He told her he uses blue spray paint. Thirty-plus years later, she writes gardening guides.
Thankfully, hydrangeas are a little less mysterious to me these days, and by the time you’ve worked through these September tasks, they should feel a lot less mysterious to you too.
1. Identify Your Hydrangea Type
Before making a single cut this fall, determine whether your plant sets buds on old wood, new growth, or both:
Check plant tags, consult a real local nursery, or look up the cultivar before touching the plant. Unless dead, diseased, damaged, or badly placed wood needs removal, put the pruners away until you have a positive ID.
If you’re still unsure what gets cut and when, we explain how and when to prune each type of hydrangea in this guide.
2. Keep Watering if September Is Dry
You may be tempted to turn off the hose in September because the air cools down. Huge mistake. The roots are still actively drinking, like my favorite uncle, and early fall dry spells can hit them hard.
Push a finger a few inches into the soil beneath the branches, rather than right against the main stem. If it feels dry down there, the hydrangea is thirsty underground.
Lay an open hose end on the soil beneath the branches (but not pressed against the stem!) and run a low trickle so the water slowly soaks into the ground instead of running off. Move the hose around the area beneath the branches if needed.
Watch out if your yard sits on heavy clay. If the soil is still wet from the last watering or rain, leave it alone. Turning the bed into an oil slick can suffocate roots fast, leaving a bundle of dead gray sticks to haul to the curb come spring.
Quick tip: Avoid aiming a spray nozzle at the top leaves, it does little for thirsty roots and can actually encourage fungal problems if the foliage stays wet.
And if September is still behaving more like summer where you live, we wrote a guide on 7 things hydrangeas need during hot summer weather.
3. Trash Infected Leaves
Are you one of those leaving fall leaf drop to “enrich the soil?” Doing that with infected foliage can set you up for the same hydrangea problems next year. Some fungal pathogens overwinter in dead leaves and plant debris, just waiting for spring moisture and humidity.
Rake up infected leaves and debris under the drip line and trash them. Your goal is to leave only healthy foliage standing.
Cleaning the ground around a shrub takes five minutes. Trying to get ahead of leaf spot or mildew once it gets going next summer takes months of effort.
Quick tip: If you have mulch, you don’t need to remove the old top layer unless it’s full of diseased material as well.
4. Refresh the Mulch
I know people who use mulch purely for aesthetics, but right now I think of it as a splash barrier.
Once any infected leaves and debris are gone, top up the mulch if it’s getting thin. A fresh layer helps stop soil and soil-borne pathogens from splashing onto the leaves during heavy rain.
Two inches thick, two inches away from the main stems. Skimp on depth and soil can splash right back onto new spring leaves during heavy rain.
That small ring of bare soil around the center matters too. Piling mulch against the stems holds moisture where you don’t want it and can encourage rot, so keep the mulch flat and the stems clear.
5. Plan Winter Protection
If you grow bigleaf or mountain hydrangeas in a cold climate where winter regularly damages the flower buds, this is the time to plan some protection.
Deep cold, temperature swings, and drying winter winds can kill those buds faster than my enthusiasm for early morning weeding.
Gather your supplies now and stash them somewhere cool and dry:
Do not wrap the plant just yet. Wait until the shrub is dormant and the leaves have dropped. It may look completely dead and bare, but that’s exactly what you want. Then:
The leaves create an insulating layer around the old wood and help protect next year’s flower buds through winter.
Bonus tip: You’re probably assuming rain and snow will soak the leaves and murder your plant anyway. The reason I like oak leaves is that they’re stiff and slow to mat down, so they keep little insulating air pockets around the stems even when they get damp.
Bare woody stems can handle some moisture. The bigger threats are extreme cold, temperature swings, and drying winter winds. And don’t panic about snow piling up on top. A good layer of snow can actually provide extra insulation.
Once winter actually arrives, we wrote another guide on 4 winter hydrangea jobs that help protect the shrub and next year’s flowers.
Two Great Ways to Sabotage Next Summer’s Flowers
If you’ve followed steps one through five, congrats: you’re almost in the clear. Now don’t ruin all your hard work by making these two ridiculously common fall mistakes.
Mistake 1: Pruning Old Wood in September
Pruning old-wood hydrangeas in fall can translate to cutting off next summer’s flowers and throwing them straight in the yard waste bin.
You are essentially paying good money to downgrade your garden and blame it on Halloween, though, again, it’s a great look if you’re trying to irritate your HOA.
Bypass the pruners unless a stem is blatantly dead, diseased, or broken.
Bad pruning is only one way to lose the show, so we wrote a guide on 7 mistakes that keep hydrangeas from blooming and how to fix them.
Mistake 2: Late-Season Feeding
Plant food in September, especially anything high in nitrogen, can trigger a burst of juicy new growth right when the shrub is supposed to be hardening off for winter.
The first early frost can damage that tender green wood before it has time to toughen up. I put the plant food away by mid-summer and let the poor thing wind down naturally.
If you’re never quite sure when that fertilizer bag should come out or go away, we explain the whole schedule in our month-by-month hydrangea fertilizer guide.
Just Paint It Blue
It might seem that hydrangeas need constant attention, with requests for the right soil pH, diet, watering habits, and trimming at just the right time. My ex had fewer demands. And yet, it’s not the plants that ended up in the trash…
