Re: Rhododendron sinogrande CCHH.8079 I have a sinogrande rhododendron given to me by someone to remember her daughter. I have now had it for one season. I had it for about six months in a large pot and had been told not to transplant it right away because it had been root pruned. Once it was transplanted very early last year (maybe March) it threw up new growth almost immediately and it was a wonder to watch the new set of leaves. But I have grave concerns for its health as its lower leaves look very sad, and there is clearly a pest...which I have assumed is weevils and despite trying both a liquid type of pesticide and some kind of biologic solution last year (nematodes maybe)...I really dont think it has worked. Hence my reaching out to anyone with knowledge about sinogrande rhododendrons. I really want this plant to live and though the newer leaves look okay I am quite worried that too many of the other leaves may fall off. Also, somewhere in my wanderings through the internet I read that sinogrande dont like it below 10 degrees and this year of course it got quite a bit colder than that. I sheltered the plant from wind but did not mulch it. Should I. This is my first post to the UBC Botanical Garden forum.
Re: Rhododendron sinogrande CCHH.8079 Pretty sure R.sinogrande sends down a tap root. They seem to like a couple inches of mulch {kept a few inches away from the stem} and it is natural for the plant to lose the older leaves, not sure how many years it holds on to its leaves. The weevils, if the leaves are notched, are active at night, so you may be able to find them with a flashlight . They are not active during daylight , but may be hiding under leaves or such on the ground. it might be a good idea to check the base of the stem at ground level in case the bark has been girdled by weevils. Hope this helps some and i'm sure more knowedgable growers than myself will reply.
Lower leaves looking very sad might be mildew. This has become pervasive on rhododendrons in this region. To understand the needs of this plant realize that it produces huge leaves because it comes from a place with copious rainfall in summer, where there may actually be a need to lose water during the growing season. An oversize leaf is also good for getting more light where there are frequent heavy clouds. A sheltered corner or woodland with good drainage, consistent summer moisture and no hot sun or strong winds will be required for it to succeed. If it does well it may eventually become large and impressive. For it to live long enough to do so a mild climate, such as might be found near a saltwater beach, is required.
Ron B ... How do you think these will hold up in the heat? I seem to get a routine number of summer days with temps 30c (86f) and above and invariably reaching 35c-38c (95f - 100f) on a few of the warmest days. I do have a garden area that Hosta is florishing, and perhaps that might be where I could site this Rhodo for best results? Also, how to these hold up with our wet snow loads? Cheers, LPN.
Snow shouldn't be much of a problem, in cold weather the leaf petioles bend so the leaf hangs nearly vertically down. Summer heat I don't know. It doesn't get that hot in the parts of Britain where the species does well (the UK champion is 7m tall). If I were to hazard a guess, probably alright provided you water it well.
I wouldn't expect any part of Vancouver Island where rhododendrons are frequent in gardens to be too hot, probably parts of the wild habitat have at least a few days of hot weather in summer also - maybe quite a few. However, low humidity combined with 100F might be punitive if not compensated for with heavy watering. Would also be important for root zone not to heat up (this is why most evergreen rhododendrons do not grow in the hottest parts of the South, the soil gets too hot). Cox, THE LARGER RHODODENDRON SPECIES (Timber Press, 1990) indicates a 5F to 15F hardiness rating and says "This magnificent plant with huge elephants ear leaves, the largest in the genus, has huge trusses to match. It does of course need shelter to attain its full glory. However, under moist, mild conditions, it may be planted in a fairly sunny position with plenty of space. A beautifully shaped specimen will result, often wider than high....Slow growing under dry east coast [UK] conditions.... We find this species surprisingly hardy in east Scotland once it gets over the tender juvenile stage at 5 to 6 years old. Two plants survived over 40 years but were killed in the 1981-2 winter. Not permanently successful in Oregon and Washington states."
I have the identical plant and it came through last winter fine except that when I had to knock the snow that would otherwise have insulated it off because I feared it would be too heavy and cause physical damage, some of the top leaves burned a bit. I wouldn't get too worried about the lower leaves as long as the top whorl is looking good. These plants are great in the garden and the leaves get larger each year as they get established. I have several different strains growing in my garden.
