Today in the Garden of a Lifetime: 'Weston's Lemon Drop' Rhododendron in Bud

The flowers of some plants—such as the fragrant blooms of 'Weston's Lemon Drop' rhododendron, which wait until mid-July to emerge—are so exciting that we forget to notice what the plant is doing the rest of the year. 


Rhododendron viscosum Westons Lemon Drop overall bloom 071315 640


Rhododendrons that flower in mid-Summer rather than the usual mid-Spring season are automatically interesting. The pale yellow flowers of 'Weston's Lemon Drop' are fragrant, too, making this shrub one of the many hundreds of plants that, for me, seem essential to any garden. 


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With such exceptional flowers at an unexpected time of the year, it's easy to forget what this shrub might be up to when not in bloom. Indeed, I tended to ignore my 'Weston's Lemon Drop' the other eleven months of the year. But this Fall's historically mild weather seems to be encouraging its buds to swell months before they otherwise would next April. In the picture below, the buds at the tips of the branches are light green and enlarged—and attractive enough to catch my eye. If they were part of an organism with not just a brain but emotions, too, I would observe that these buds are enjoying getting ready to do their Next Big Thing.


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Actually, there are two Next Big Things, and they happen simultaneously. The large bud below isn't alone: There's a ring of much smaller buds around its base. The large bud will most likely develop into flowers, while the smaller ones will, absolutely, develop into next year's crop of vegetative shoots.


Rhododendron viscosum Westons Lemon Drop bud for close up 121915 640


The stem below shows the pattern both retro- and prospectively. At the center is the remains of last Summer's flower cluster. Four side shoots grew over the Summer from its base, and they are tipped with just the large-size buds that can be expected to mature to flower clusters this coming July.


Rhododendron viscosum Westons Lemon Drop last years flowers plus new growth 121915 640


I'm waffling a bit—"can be expected", "most likely"—because, as I say, I had let my attention wander from Rhododendron 'Weston's Lemon Drop' when it was not in flower. Will each of the four satellite buds develop into a flower cluster? Or are these terminal buds large simply because they are at the stem tips? Could one or all continue to develop vegetatively instead?


Each Fall, every stem of a plant hardy and woody enough to maintain its above-ground growth over the Winter doesn't just stop growing willy-nilly. It finishes up tidily for the season, while also enabling itself to pick up next Spring right where it left off. The terminal bud is, literally, the end-of-season wrap-up for the stem's growth point. It serves as that tip's protective cap on what will once again become a very active "construction zone" when growth resumes in the Spring. It's also the repository of the growth elements that will, appropriately, spring back into action in April and May: the nascent buds (if they are in the cards) and the tissue that will begin producing additional stem and leaves.


Woody plants that flower in late Winter or Spring are only able to do so because they had begun preparing for those Spring flowers the previous Winter and Fall. Bud formation began that prior year, so flowers could become fully formed quickly as soon as benign weather arrives. Plants that flower later than Spring might not even begin to develop buds until after they've already produced new vegetative growth; both flowering and vegetative growth, then, are originated as well as matured in a single growth season. Most rhododendrons are early-season bloomers and, so, initiate bud formation the previous year. But what about the forms that flower in the middle of the Summer? The flowers of 'Weston's Lemon Drop' usually emerge the last half of July; I grow another rhododendron, 'Pennsylvania', that doesn't start flowering until August. Do these Summer-flowering rhodies still begin forming buds the previous year and, if so, are their buds in evidence week after week after week, Spring into Summer, before finally maturing to flowers?


How have I not already noticed the growth patterns that would provide these answers? 


Despite this "budding" suspense, the real mystery of the shrub is how any given stem's growth in one year determines its growth in the next. It might seem as if the only options for a stem's tip are to grow for one season, then form a protective terminal bud that is (probably) going to mature to flowers the next, and is ringed by secondary buds that will definitely mature to further stems. But the habits of some of the stems of this particular 'Weston's Lemon Drop' are different.


Look below, at the same shot of the plant overall. A few very tall branches have sprung from the shrub's base. They pierced the original canopy and soared twice as high before adopting the more typical "grow a stem for a while then top it with a starburst of side growth" strategy.


Rhododendron viscosum Westons Lemon Drop overall 121915 640


Looking closely, it would seem that, sometimes, the central growth point from one season does not mature to a flower cluster the next: Only some of the whorls of side stems are surrounding the remains of flower clusters. Yes, radial side stems are still formed, but around a new central growth point that has produced another season of vertical vegetative growth. 


Rhododendron viscosum Westons Lemon Drop upper stems in bud 2015 12 18 640


These unusually tall stems form a foot or two of leafless and side-stem-less new growth before forming a whorl of side stems. 


Rhododendron viscosum Westons Lemon Drop mid stems 2015 12 18 640


Remember that such a length of "clear" stem (one without branches or leaves) couldn't just stop growing for the Fall, as if it were a water pipe with the water turned off but the end left wide open. Yes, the water—the sap—does stop flowing up from the roots. But the end is also capped for the Winter by that terminal bud. 


Further, although that cap, that terminal bud, is at once the stem's stopper for Fall and Winter—and the point where new growth begins to be produced the following Spring—it's unusual for there not to be surviving evidence of the cap even if the stem stopped growing in the Fall right here and then resumed growth in Spring from that very same place: some sort of scar or change in angle or thickness of the new section of stem. These vertical stems of 'Weston's Lemon Drop' show very few such markers, and the ones they do show—such as a whorl of side branches, or the continuation of the vertical growth arising from a kind of knobby joint—are prominent.


Even if every side branch in the picture below were cut off right at the point of attachment to the main stem, their ridged points of attachment to that stem would remain. These completely disrupt the smooth vertical patterning of the bark of the straight stems above and below, leaving no doubt that, yes, they were the point at which that stem took a break from its upward rush to form the whorl of side stems.


Rhododendron viscosum Westons Lemon Drop whorl new stem showing joint122115 640


A clear section of stem, then, shows the minimum length that the stem grew that season: a foot or even two. That's a lot. We don't usually think of rhododendrons as producing vertical stems of such length and quickness of growth that "shoot"—as in a sudden growth spurt more typical of bamboo shoots, where the "shoot" seems entirely literal—seems appropriate.


Growth could even be so fast that there's time for more than one such clear length of stem a year. It could rocket up for a foot or two in Spring and early Summer, form a whorl of side stems and, then, from the center, form yet another vertical shoot in mid-to-late Summer. Did these ultra-tall stems form over just one season, then, or over two or three? Alas, I hadn't thought to look as they developed. I will now. These stems' further growth habits, and those of any such additional shoots, will be on my radar.


The meta-question here is why did these tall stems form at all? The shrub was thriving for years at its medium-height lifestyle. What changed (and when) such that two or three shoots twice as tall as had ever been produced before were now not just possible, but the only "sane" option, the shrub's then-new Next Big Thing? And are they the new norm or an aberration? Will further new growth be the staid grow-six-inches-then-produce-a-whorl-of-sidestems type? Plus, after what seems to be, at the most, two or three seasons of fast vertical growth, do the stems' need to produce flowering clusters at their tips instead of another spurt of vegetative growth become imperative? Can assumption of life as flowering and just-slowly-growing adult stems be postponed for only a while? 


Look at the very base of the shrub. All of the stems that shot the highest the fastest have emerged from the base, not from older growth. This makes sense, in that the older growth might not be capable of expanding quickly enough—to increase the bore and number of its feeder pipes, so to speak—to sustain the rush of these young verticals.


Rhododendron viscosum Westons Lemon Drop base 2015 12 18 640


Will the flowers of these skyrocketing basal shoots be the same as those of the older lower growth? Yes. Named forms of rhododendrons are propagated by cuttings, not by grafting. There's no separate rootstock to worry about, producing fast-growing vertical stems whose flowers don't at all match those formed by the older, slower top growth. As with spirea, and weigela, all rhododendrons are "own root." Rogue basal stems that, on a grafted rose, would have been cut out ruthlessly can be retained—or not—at the gardener's discretion.


Do these "rogue" stems of 'Weston's Lemon Drop' have enough appeal to merit being left in place? Yes! Look at their bark, which is in distinctly warmer shades of brown. And their unusual tall-and-narrow habit (at least so far) is always welcome in beds such as mine, where there's always a need for more space for more plants.


Thanks to this Fall's swollen-out-of-season buds, I'm now aware of a huge "bouquet" of questions about this shrub's month-by-month, year-by-year habits. It will be a pleasure to watch closely enough, often enough, to discern the answers. Each year's explosion of July flowers will still be fantastic—but, now, also just one of many fascinating annual markers of what, really, is going on as this shrub continues to mature.


Instead of tying a string around my finger to remind me to check in with this shrub often, I've tied twine around the shrub's whorl of side-stems. Then, we can all follow what happens in 2016 to each of its terminal buds. By June, we'll know whether any given bud's intention was to form flowers or just more leaves and stems.


Rhododendron viscosum Westons Lemon Drop twine bow 122115 640


We'll also know answers to some of the other questions the buds have brought to my attention. Not least: Are the now-swollen buds at risk if the Winter becomes rough? Once swollen, buds can't "unswell." Stay tuned.



Here's how to grow a pink-flowered cousin, Rhododendron 'Pennsylvania', whose handling is the same. It flowers even later: into August! 

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