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At the suggestion of @Jurp I purchased three clethras. The motivation is attracting wildlife, and having nice summer fragrance. Now however I don't know what to do with them, I'll explain the reason in a moment.

The nursery says they are 1m high max. They swear it is true. However, they delivered all three plants exciding their max height! :-o All are around 1.2m high. When I brought this to their attention, they just stared blankly at me.

If I search the internet, max height varies between 1m and 2.5m. I am afraid I will plant them in wrong place. Can you help?

Adult unpruned clethra 'Pink spires' should look like this:

enter image description here

VividD
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1 Answers1

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Perhaps they meant the delivered plants would be 1m in height, or thereabouts, it's common for nurseries supplying via mail order to quote the height of the plants they're actually sending out. The anticipated height for this plant is 1.5, sometimes up to 2m or more, or 6-8 feet, and its usually taller than it is wide. No one can predict precisely how tall and wide yours will get, depends on climate and growing conditions, so I suggest you plant bearing in mind the possible ultimate height and spread of this deciduous shrub.

They do get tip dieback in cold winters, and pruning is probably advisable after a time - you may also be able to keep them in check by reducing their height if necessary, information on pruning here http://homeguides.sfgate.com/clethra-alnifolia-pruning-tips-42582.html

Bamboo
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  • Great answer and great link! It is especially conforting that the size can be (to a great degree) controlled by pruning, and that the plant finds a way to grow regardless of pruning style (hard or light). – VividD Dec 11 '17 at 22:12
  • I'll back up Bamboo - in US measurement, the plants are sold to be 3' wide by 5' tall (so, about a meter wide and 1.6 meters tall?). I will say that they do not take shearing well, so if you're going to prune, treat the shrub like a tree and cut back to wood - don't leave stumps (they usually just die back to the wood anyway). I have two of them, and they're fairly slow growing - if you follow the "right plant, right place" design rule, put them somewhere where you'll want to see a 1.6-2 meter shrub (I've never seen one of these taller than 5', by the way - even old ones) - no pruning then! – Jurp Dec 12 '17 at 00:22
  • Ok, thanks, @Jurp , I may post another question in a week or so with photos of my examples about initial (after planting) pruning of clethras. Or perhaps I shouldn't touch them for a couple of years, or remove only dead wood. I have no idea what is dead now - everything looks woody to me, I would rather wait for spring to see what part of the plant is actually alive. – VividD Dec 12 '17 at 00:36
  • @jurp Unfortunately, I just found the data that clethra is moderately acidofilic... My soil is not acid. This will be an uphill battle. – VividD Dec 12 '17 at 07:06
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    @Vivid - Ohio State Univ (excellent Hort program) shows C. alnifolia at "various pHs"; other sites show "slightly acidic". Morton Arboretum (Chicago) shows pH as "tolerant of pH". It appears that the species can tolerate pH down to 4.5 (US Dept of Ag), but the cultivars seem to be more tolerant. If you have to lower pH, I'd recommend either elemental sulfur (two applications per year) or Ammonium sulfate. My own soil is on the acidic side (due, I think, to having been an oak forest for hundreds of years) (I've seen them in more basic soils). Water can affect height; less water=shorter plant. – Jurp Dec 13 '17 at 00:18