I was browsing through a couple local nurseries lately and noticed Sea Buckthorn plants on sale (discounted). I guess the nurseries are trying to clear out inventory that didn't sell over the summer. These plants had both male and female grafted onto a single plant, so two separate plants aren't needed for pollination. I am tempted to go back and buy one. I like the fact these plants are cold-hardy, nitrogen-fixers, produce very healthy fruit, and grow in poor soil. However, I am wondering if these plants are invasive. I had read that Autumn Olive are good, but invasive, so decided against them. Does the same problem apply to Sea Buckthorn? Is Sea Buckthorn invasive in the Lower Mainland? Or parts farther north (like Williams Lake)?
Depends on your soils. On sunny, well-drained coastal sandy soils, Sea-buckthorn is very vigorous and suckers widely, so outside of its native range I'd say yes, very likely to be invasive. Much less so on other soils, and not at all in shade. I like it, but it is a valued native species here. I'd not recommend it for BC.
Apparently not much spreading in BC so far. CPNWH Search Results (pnwherbaria.org). With the same source not returning any collection records for the United States at all. Otherwise there is this: sea buckthorn, Hippophae rhamnoides Rhamnales: Elaeagnaceae (invasive.org). BC collections of the Elaeagnus on the other hand have been more numerous. Mostly single individuals rather than thickets of it, but still perhaps a basis for possible concern about an increased presence in the future. CPNWH Search Results (pnwherbaria.org)
Hmmnn... oh no! It seems like all the nitrogen-fixing trees or shrubs I know about are invasive. Are there any nitrogen-fixing trees or shrubs that are not invasive? Ideally, plants that are native to B.C.?
Red alder (Alnus rubra) is a nitrogen-fixing, hardwood tree which, being native, cannot by definition be called invasive. (This was pointed out to me by @Daniel Mosquin.) Only you can decide whether its aggressive characteristics suit your needs. It does prefer moist soil. E-Flora BC Atlas Page
Ditto for Sitka Alder Alnus alnobetula subsp. sinuata and Thinleaf Alder Alnus incana subsp. tenuifolia, though the latter only in interior BC. Buffaloberry Shepherdia canadensis is also a BC native and in the same family as Sea-buckthorn so is also N-fixing; this might be your best option as it also has (at least semi-)edible fruit.
I agree with Ron. It suckers but that doesn't mean it's invasive. The UW Arboretum plants have not taken over in decades of growth. I grew a couple at the Good Shepherd Center in Seattle for many years with minimal hassle. A great plant with lacy leaf, willow-like, rather viciously armed but superfood.
See my post above - it depends on the soil. On sand dune systems (its preferred habitat), it can be expected to be very invasive. The seeds are readily dispersed by birds, so not a good idea to plant it within bird dispersal range of dune systems.
