Pruning Clethra summer sweet?

deanna in ME Barely zone 6a, more like 5b

7 years ago

Can I get some advice here? My Clethra is 'September Spice' so it blooms later than most. But, it gets too tall. It's also in quite a bit of shade. It is what it is, so I'll work with it. But, I need some CLEAR advice.

Regarding when to prune, websites say to prune in spring before buds have formed on new growth. What does that mean? "Spring" is just so vague. A better clue for me is what else is happening in the yard. Forsythias here still look fantastic, some are past prime. Tulips are just finishing. Only the earliest rhododendrons have flowered. My Aslcepias incarnata has just now emerged and is all of about 2 inches tall. Everything else is emerging much more quickly, but Asclepias loves to be late. Bleeding Heart are blooming, but no early geraniums are. Nepeta are almost a foot tall now. Hostas are definitely well on their way but none are to full height/shape. As for the Clethra, it has just started to leaf out. How long can I wait before I've cut off this year's buds on the Clethra?

Also, where to prune. I've read I can hack it like a lilac or forsythia, bit I've also read to only prune a little for shape. I need to reduce height. I thought I cut it back hard last year and it still grew tall. I wonder if my shade is making it stretch high to find sun. How should I prune?

Thank you!

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Comments (3)

gardengal48 (PNW Z8/9)
7 years ago
If it is just starting to leaf out, you don't want to waste much time. Prune it now. Generally it only requires shaping but since it blooms on growth produced this season, you can take it back pretty hard.

It will also grow and bloom very well in quite heavy shade. I couldn't find any reference to a cultivar called 'September Spice' - 'Ruby Spice' (blooms July-August and gets 6-8' tall) and 'September Beauty' (blooms 2 weeks to a month later than others and gets big - 8-10' tall and 6-8' wide) are the closest I could come. But that should provide a clue as to potential size.
deanna in ME Barely zone 6a, more like 5b
Original Author
7 years ago
It's September Beauty. Sorry for the error. It was here when we moved in, planted in front of our driveway light, but somehow I missed the 8-10' tall part. No wonder it's getting too tall! I think next summer I might need to find a new home. I must say, though, if its supposed to be 6-8' wide...I'm thinking it might need some loving care. Maybe a good boost of compost. Mine is exceedingly spindly. I couldn't image it being even 3' wide. Missouri Botanical Garden says it is "densely-branched." HAHAHAHAHA!! I know it's September Beauty because the tag was still on it. Must have planted just before we purchased the property. It also blooms VERY late.

It's possible the spindliness is because we have had two dry summers in a row. We've got the acid part covered just fine, but it hasn't exactly been moist for a couple of years. Fingers crossed for more rain this year!
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Skip1909
7 years ago
last modified: 7 years ago
They are leggy plants with a lot of stems. They are the dominant understory plants here in sandy low lands where the water table is high, growing in vast colonies underneath mixed oak, beech and pines. They will send out rhizomes and grow new plants from the roots, I would think you could prune them fairly hard. Maybe 'Hummmingbird' or 'Sixteen Candles' would be a better cultivar for your spot, or a different shrub all together since they are suited to moist conditions.