I have two large and healthy monkey puzzle trees in my front yard. I am interested in planting under the trees (possibly ferns), but the area is currently barren and the soil is hard and clay-ey. I was told by someone that monkey puzzle trees secrete a toxin that keeps other plants from growing around them. Does anyone know if this is true, and if so is the toxin secreted through the roots, or does it reach the soil from the many "needles" that fall off the tree?
The fallen leaves may acidify the soil a little, but I'm not aware they contain any toxins. It is more likely just due to the tree using up all the water in the soil, making it too dry for other plants to grow easily (the hardness of the clay would certainly indicate this is happening). You could try plants that generally do well in shade under conifers, such as Mahonia or Gaultheria.
I am sure that Monkey Puzzle trees do not secrete any sort of toxin. There is a large specimen at the entrance to a park in my home town which is underplanted with a whole load of stuff, Roses, Forsythia and Hydrangea being the only ones I can remember at the moment. Compaction does indeed sound like the most likely reason. I doubt the needles would effect the acidity of the soil too much either. Generally small branches fall from the trees rather than individual needles and in my experience, they do not break down or rot into the ground for a very long time. They are still sharp critters for years after!
Thanks for your advice. I have noticed that the thick branches don't let much rain reach the ground below the tree. Hopefully better soil and irrigation will do the trick.
