There are actually some very large Arctostaphylos. David what would you want to achieve? Arbutus unedo is certainly better adapted to garden culture than most of the sexy Arctos - is that what the goal would be? Or are you simply curious about the cross-genus aspect?

Oh dear, Sara, I shouldn't post straight after coming in from next door's Christmas drinks party ;-) Normally I would have checked Arctostaphylos, both spelling and species. I just jumped to A. uva-ursi, the only one common over here.

No problem! One of the reasons that gardeners in other areas don't know most Arctostaphylos is that they generally don't do well in cultivation. Their roots take offense at both real and perceived slights. Some of the larger ones are very dramatic but soooooo difficult to grow.

"Their roots take offense at both real and perceived slights."

Which would be the precise reason to replace them with another set of roots ;-)

I had just spotted Ian Barclay's list of Arctostaphylos for sale and lamented the fact that they are ungrowable in the eastern US. I mean, really ungrowable. When Bill Cullina says any of the hardier, interior species won't even grow for him, on rocky soil in airy New England...that's the end of that conversation. (I haven't met the esteemed Mr. Cullina to have this conversation; but I have read his account of finding them impossible to grow) I don't know which ones he tried but the impression I got from the article is it was any possible hardy ones. I myself saw beautiful, peeling red-barked manzanitas just as the California Zephyr descended below the snowline in January 2011, at an elevation of over 4000 ft in the Sierra Nevada - so those would be at least zn 7 hardy if not zn 6.

BUT there's no species even within the genus as an alternative rootstock. So you'd have to graft to something closely related. Arbutus unedo will grow in much of the southeast, at least if reasonable sited. But I suppose on the molecular level their cells might not be able to fuse or whatever actually happens during grafting.

I asked Phil Van Solen, who is the reigning expert on CA natives around here (has run a CA natives nursery for decades) and he has never seen any grafting using Arctostaphylos in any way. However, your question is really broader - about cross-generic grafting, for which you would want to ask grafting experts. Also, both of these genera are Mediterranean - want dry summers with cool nights. Very tough to duplicate that in a place with moist summers with warm nights. From what I know of conifers, you are correct in believing that the rootstock is the key to success. The SE folks graft all Abies onto Abies firma, for example, which is native to Japan. Since most Arctostaphylos are difficult for us to grow in gardens, and we are in/near their native habitat, you have a challenge. On the other hand, if you figured out a way to do it, you'd have a receptive audience!

Eventual stem diameters of scions and stock need to be comparable or you eventually end up with a visually unpleasant mis-match. Another occurrence that can often be a spoiler with grafted combinations is delayed graft incompatibility. I've heard that when this started to be seen in attempted commercial plantings of cross species grafted walnuts the scions were actually dropping off of the stocks clean, the unions never having fused completely - after about 10 or more years of top development.

In my area the most visible limitation of susceptible kinds of manzanitas (including the locally native species) is pathogenic spotting and blackening of the leaves due to dampness. However Arctostaphylos manzanita seems to do pretty well here and has made at least a few conspicuous, lasting specimens of some size. Because it is comparatively tractable, handsome and large growing it might be the best bet for attempted grafting onto strawberry tree.

Have never seen Arctostaphylos manzanita in the trade. It is native around here, but the only ones I've seen have been in the wild (or 'domesticated' in someone's rural, shrubby property.

" Also, both of these genera are Mediterranean - want dry summers with
cool nights. Very tough to duplicate that in a place with moist summers
with warm nights."

True but as I've noted before, Arbutus unedo and A. X andrachnoides will grow in the south. They may not exactly thrive and last for centuries, but they aren't going to keel over after this first week of summer as A. menziesii would. Coastal Greece and Calabria/Sicily/Tunisia/etc., even parts of Spain, are muggy in a way that California is not. Not as muggy as the SE, but close enough that Mediterranean plants will often grow in the southeast whilst CA plants will not.

Right, we don't do muggy! A. menziesii will keel over if I try to grow it HERE in a cultivated situation, even though it's all over the roadsides . Quite a few of our CA natives are really garden-unfriendly. The only Arctostaphylos that is basically bullet-proof in the garden is A. d. 'Howard McMinn', although a few others are reliable if given the right situation.

A. manzanita is one of the main species at retail outlets here. More than one cultivar is offered.

http://www.laspilitas.com/nature-of-california/plants/56--arctostaphylos-manzanita-dr-hurd

http://www.laspilitas.com/nature-of-california/plants/84--arctostaphylos-manzanita-x-densiflora-austin-griffiths-manzanita

https://search.yahoo.com/yhs/search;_ylt=A86.J79VfVdY530ACKQPxQt.;_ylu=X3oDMTEwbHI2ZzczBGNvbG8DZ3ExBHBvcwMxBHZ0aWQDBHNlYwNyZWwtYm90?p=arctostaphylos+manzanita+dr+hurd&type=osf01s1&hspart=avast&hsimp=yhs-brwsr001&ei=UTF-8&fr2=rs-bottom%2Cp%3As%2Cv%3Aw%2Cm%3Aat-s&fr=yhs-avast-brwsr001

https://search.yahoo.com/yhs/search;_ylt=A86.J79VfVdY530AC6QPxQt.;_ylu=X3oDMTEwczI1NTJsBGNvbG8DZ3ExBHBvcwM0BHZ0aWQDBHNlYwNyZWwtYm90?p=arctostaphylos+manzanita+st.+helena&type=osf01s1&hspart=avast&hsimp=yhs-brwsr001&ei=UTF-8&fr2=rs-bottom%2Cp%3As%2Cv%3Aw%2Cm%3Aat-s&fr=yhs-avast-brwsr001

Interesting. Have never seen it here.

" Also, both of these genera are Mediterranean - want dry summers with cool nights". Just a small point. Arbutus unedo grows well in southern and coastal areas of the British Isles where the summers are very far from dry. It is considered native in the SW of Ireland.

It's a very tough shrub here - way, way tougher than our native Arbutus. it can tolerate poor drainage (which goodness knows the native cannot), variable watering, neglect, wind, etc etc. So I guess it's not surprising that it grows well there. However, what tanks conifers in the SE US is warm nights, not the humidity so much. The plants don't have the opportunity to 'shut down' at night.

The problem is the imprecision with which we (people generally, not just gardeners) use the term humidity. There are plenty of places that are always very humid but never have high dew points. For example somewhere like the Scilly Islands - coastal UK generally - and the west coast of NZ. The extremely warm nights in the SE US are more related to their dew points being very high. But I've noted Brighton in early Sept. was a bit muggier than I expected it to be. The Pacific waters north of Santa Barbara CA probably stay below 60F all year, while the English Channel might have been as warm as 65F? Thus making the air a little more humid: though still in a place that is quite far north and where the overall atmospheric circulation is with relatively dry, comfortable air. There's no superheated Gulf of Mexico pumping sauna like air, as happens to us in the eastern 2/3rds. Some friends of my parents who are Irish but have lived in the States for 30 years admitted to being back in Ireland and finding the air uncomfortably muggy sometimes, because they had become used to eastern USA air conditioning and our very dry interior air in buildings. I experienced the same thing in AU & NZ. People just don't "sweat" (no pun intended) the air being a little muggy in a building. (or in one case the train: the supposedly luxury "Tranzalpine" train in NZ felt like a damp locker room to me. The carriages are tightly sealed because the diesel locomotives have to go through some tunnels...but they really need a damper that opens for the rest of the trip. I found it vaguely disgusting. It makes the odors of other people carry over more than they otherwise would. The California Zephyr also has to close the vestibules to pass through the Moffat Tunnel: but in a place with the bone dry air of the Rockies, being sealed up to the outside is a *good* thing!)

Further complicating this, however, is the the ultimate culprit with many plants (but not all) is probably soil temperature, and the somewhat related factors soil structure and degree of moisture variability. So this explains why ironclad rhododendrons like 'Mars' are seen in southern Japan and not the SE USA. We have the triple whammy of searing sunny periods to warm the soil up, which is clay with a terrible structure, and sudden, voluminous downpours in summer to saturate the soil and drown roots. While Southern Japan has aerated volcanic soil, cloudier summers, and more steady rainfall. Even though the raw dew point and temperature averages are probably similar to parts of the SE US.

Anyhow, back to the matter at hand! I will scrounge around to try to find someone who can make one of these grafts...maybe Ian if I can get him interested. There's no harm in trying. Or no harm to me anyhow, if I can get someone else to do the hard part which is the grafting. I just have to buy the plant if the graft appears to take. In researching the Ericaceae of CA, I found out there are others I'd never even heard of: Comarostaphylis diversifolia, Summer Holly
Probably not quite that hardy (or tolerant to eastern conditions!) but interesting to know about. Wow!

There's a Summer Holly against a wall on the heavy* soil of the Carl English Botanical Garden in Seattle. This is of course not a torrid summer situation.

http://arthurleej.com/p-o-m-Dec04.html

Jacobson also did a Plant of the Month about Arctostaphylos manzanita, with local pictures.

http://arthurleej.com/p-o-m-Mar08.html

*On another part of the site forming a pond during winter

The reason I like Bill Cullina's comments so much is because he speaks from first hand, field observations. I have several of his books and here's what he says about Archostaphylos uvi-ursi. This is certainly one of our finest groundcovers, and also the most adaptable species.... Bearberry will survive heat and humidity that will kill other species, provided that it has perfect drainage..... It is intolerant for all but poor, acid sand.

In the 90's I belonged to the IPPS, I remember a Long Island bus tour to Planting Fields arboretum. On the way there we passed acres and acres of dwarf pine and bearberry growing in pure, xeric sand. The same can also be seen in some parts of the NJ Pine Barrens along with huckleberries, trailing arbutus and sweet fern. That's one reason why Botanical clubs love to go botanizing there.

Devin shows bearberry in its natural setting in this youtube

Thanks sam. Unfortunately I can't find the citation of him trying several hardier western species, but I know I read it somewhere! Bearberry is the only one kinda native to the eastern US...albeit at higher elevation and/or latitudes...so it would make sense it has a little tolerance of heat and humidity. I am surprised they are found as far south - and as far down - as Long Island.

OOPS - wasn't my fault! Someone spelled it wrong in this thread haha. Anyhow they have one Bearberry at Longwood...so at least if I want to grow that tiny, boring one, I have a chance haha.

What kind do you think this is? So far it looks like Arbutus x andrachnoides. Owen Johnson says in Champion Trees of Britain & Ireland (2011, Royal Botanic Gardens, Kew) that this hybrid is "never long-lived", lists one measured as being 17 m x 132 cm (below forking) during 2003, from an 1891 planting at 'Woodlands', Alvechurch, Worcs. (Another, at Inzievar House, Fife, is listed as being 24 m x 76 cm in 2001 "when probably dying of honey fungus").