No. The soil will dry out in about 5 seconds in summer, and 9 inches isn't enough for the roots even if it didn't dry out. In fact, I suggest you limit plants in that area to succulents like groundcover sedums. And even then, they may struggle in a dry spell.

The roots can grow laterally; i'm PRETTY SURE i've seen this in nature - on rocky cliffs and so on.

My concern is that in winter, the roots will not be insulated from freezing and will be damaged or killed; zone 6b: down to around 5 bellow zero.

Yes, you probably have seen that in nature. However, in that situation, the plant grew from seed and sent it's roots into cracks and crevices. You have to start small.

Drought will be much more your enemy. Low winter temps will hardly be an issue with root systems; soil is a fabulous insulator.

Viburnum lentago is native much farther north than zone 6b. I have purchased this species from nurseries growing in zone 4 (-30ºF). Nannyberry is much less happy with high summer soil temperatures. It performs very poorly here in central KY, where we can reach zone 5b/6a temps regularly, and I have relatively deep clay loam circumneutral soils.

All that said, I don't have any good advice for a different species of viburnum to attempt on such shallow soil conditions, except...Viburnum molle.

Kentucky viburnum (very similar to arrowwood, Viburnum dentatum) grows quite happily in its native haunts on shallow soils over limestone outcrops. If you can reproduce those conditions, then you may have success with one of the rarest viburnums in the US.

Hi,

What is the true maximum width size (at full maturity) of an unpruned Amelanchier canadensis, Canadian Juneberry/Serviceberry. I've seen large Amelanchier arborea examples that were around 35' wide. The majority of all internet information on A. canadensis (as well as A. laevis and the x grandiflora hybrids) is that the tree gets only 20' or 25' wide. I have a feeling that this is not really true; that the real maximum width is really around 35' and probably much more for a mature A. arborea.

Also, what is the true width and also height of Viburnum lentago. Supposedly, 30' tall if trained as a single-trunk specimen and only 15' tall if left to its natural shrub inclination; and 12' wide. What would happen on its own, un-trained?

Thanks,
Steve

njbiology wrote: "My concern is that in Winter the roots will not be insulated from freezing and will be damaged or killed...."
As you drive around NJ you can no doubt notice the number of poly houses used for overwintering container stock. The vast majority of these are unheated. They even use white poly to prevent the houses from heating up on sunny days. The root zone is sub-freezing on a typical winter day. It just so happens that viburnums and serviceberries are perfectly tolerant of root freezing. Some mid-Atlantic growers only put them away to protect them from deer and rabbits, not the cold.