Be Careful with Shore Pine in the Winter-
Shore Pine is one of North America’s most beautiful two-needled pines, with short bright green needles and great bark. It has similarities to many other smaller pines which often have multiple crowns, like pinyon pines. Shore pine does have one distinct difference however, and that (appears to be) cold hardiness.
I say ‘appears to be’ because it’s more of a hunch. It does seem that at least some populations of Shore Pine are not as cold hardy as its relative, the continental, mountain-dwelling Lodgepole Pine. In some respects this is not a surprise, since many Shore Pines live close to the Northwest coastline in the same sort of zone as the Japanese Black Pine does. Anton Nijhius of Vancouver Island, Canada collects many Shore Pine, and says that some of them live at 4,000 ft in a lot of cold on the Island, so there is definitely some room for argument here, and possibly different strains.
That Shore Pine does fantastically in the ground in Portland Oregon, where it can get down to 10 F in rare storms, and yet does less well in pots (occasional branch death, tree death) supports the idea that it is a root hardiness issue. But again this is a bit of conjecture.
Japanese Black pine roots begin to die at about 12 F / -11 C. Given what I’ve seen and experienced, and other anecdotal stories from others who otherwise have excellent horticultural skills in colder climates than mine, Shore Pine bonsai can be even more sensitive to cold than Black Pine bonsai, and so my recommendation is that Shore Pine bonsai should be protected from strong freezes. Perhaps even 50 miles inland from the coast, in more continental climates where everything is more severe, Shore Pine should be protected in the winter.
Given the natural beauty of the plant, there are simple solutions that can allow us to enjoy this native tree as a bonsai. If you live in a region that frequently gets below 25 F / -4 C in cold snaps, consider taking protective measures starting in fall.
For more, please visit these posts about winter and our bonsai:
Post-note: Cold hardiness for trees in pots is a massively different matter than cold hardiness of plants that are normally put in the ground, and that we read about in gardening manuals. A plant with a cold hardiness of Zone 4 might not survive in a small pot sitting on a bench in that zone. Root hardiness is the issue that bonsai practitioners need to be aware of, and that information is less easy to find.