British Columbia: Toxicity under araucaria araucana

We have about twenty osmanthus delavayi planted under a monkey puzzle tree which are dead six months later. Does anyone have knowledge of alleopathy as a result of planting under monkey puzzle trees or California sequoia?

 

Probably has nothing to do with the tree, unless it blocked the rain too much for them.

 

Doesn't appear to be a light issue: there are several of the same plants planted at the same time with less light doing just fine, a positive characteristic of osmanthus. The dead plants are under the dripline of the tree including the south side which gets lot of light. Not salt from the driveway either: we never used salt and the rest of the adjacent plants are doing just fine. The mystery broadens...Thanks for your contribution.

 

Continues to sound like it was too dry under there.

 

My first inclination is to blame drought from root competition, but it appears that related Araucaria species (A. angustifolia and A. cunninhamii) have been studied for their allelopathic effect. See: Braine, Jessie Willian, et al. "Allelopathic effects of Araucaria angustifolia needle extracts in the growth of Lactuca sativa seeds." Journal of Forest Research 17.5 (2012): 440-445.; and (for A. cunninhamia [sic]) Singh, Harminder Pal, et al. "Allelopathy of gymnospermous trees." Journal of Forest Research 4.3 (1999): 245-254.

It is therefore not outside the realm of possibility that A. araucana has some of the same or related compounds present in its tissues and that this might be responsible for the curious death of these Osmanthus delavayi. To be sure, I have seldom seen plantings under monkey puzzles, but the assumption is that root competition is the limiting factor. I would be interested to hear from others who have had trouble (or no trouble) establishing plants under these trees. What about weeds?

 

It is true these trees tend to be a solo act. But killing shrubs within 6 months would be quite a demonstration of lethality. And why the worst effects in the same part of the planting that would probably also be the worst for dehydration? Other kinds of trees and shrubs that are blatantly allelopathic have produced a uniformly empty dead zone around their stems. However, I don't know if this is universal.

 

Bracken and grasses at least have no problem growing under A. araucana, but other plants could differ of course. Not an easy one to make observations on, as most people like to have their araucarias in the middle of a lawn, rather than in shrubberies.