I had tried to get this answered somewhere else but alas the shadowbanning Karen at a 'leading internet gardening forum' is up to her old tricks again so there's no guarantee people are actually seeing my post. I'd hoped she'd gotten her vendetta against me out of her system...apparently not! I'm aware S.s. are near the limits of their hardiness here so no need to generally rehash that topic. There's a couple 70'+ trees in the Philly region that are the northernmost on the US east coast. I have a 'Chapel Hill' that has a perfectly normal Christmas tree shape. Neither 'Soquel' nor 'Chapel Hill' have ever been seriously damaged here, but 'Soquel' did lose its leader in the first polar vortex winter in 2012-2013. It is still struggling to restore it, apparently! Since then the tree has seemed to grow preferentially fatter than tall. You can see there is still some kind of dieback. I'm perfectly willing to accept the possibility that - ok - this variety is just not quite hardy enough and in spite of getting through most winters now undamaged seeming, the leader is just more prone to cold damage and this will be an on-going issue. Fine. I am just soliciting advice along the lines of - is there any other factor that could be contributing? Are redwoods just slow to restore their leaders? I think conifers are, generally, compared to angiosperms. Frankly in the non-maritime climate parts of the Bay Area like Davis, I saw some really awful looking redwoods, including dead looking tops. Obviously there, it not an issue of cold damage. So maybe they just respond to stress by losing their leaders? In any case as I posted on the other forum, the good news is I don't want this tree here anymore, healthy or not, because there are plenty of other large trees nearby already. I will try to ground layer it preserve the clone (although it's somewhat commercially available) and move it to a more 'experimental' part of the garden. If it continues to have these issues there, it will be permanently deaccessioned. 'Soquel' does come from near the southern end of the species range FWIW. Although the climate isn't hugely different from the northern end!
They're not normally slow to replace lost leaders; I'd think it is just ongoing repeated cold damage on the leader (which is the last to finish extension growth in autumn, so yes, more vulnerable). In the California Bay Area, it'll be drought, rather than cold, that causes the dieback, but the effects are much the same.
The Stratosphere Giant (typically in the neighborhood of 379 ft. tall at any one time, as of some years ago) repeatedly dies back and then regrows so as to be neither an example of the mythological yet repeatedly stated phenomenon of height growth of still healthy trees normally coming to a complete stop at some point nor a specimen that is managing to progress to a significantly taller height range. With it being believed that the underlying issue is an inability to keep the entire top hydrated during dryer years. With in addition this particular redwood - while still towering - being located toward the dryer end of the precipitation range for giant coast redwoods to be possible in their native area. So, when times are good it grows new leaders and when they aren't it dies back - a photo of the extreme terminus of the Giant I saw awhile back showed a bare and dead central leader with a set of surprisingly vigorous looking (and still living) replacement attempts arranged around it.
Thanks for the replies. I agree, Occam's razor dictates things are actually what they seem here and it's simply that growth not hardening as well as the rest of the growth, so this cultivar is just ill-adopted to a 'marginal' climate. Fine. If I'm near the imperial city sometime in the fall I will try to get cuttings from the (perfectly upright) trees growing in the suburbs down there, if I can remember where to find them. Send them out to be mist propagated.
