The picture below shows a row of Rhododendrons and one tree (Gleditisa triacanthos). While I removed some groundcovers the owner of this corner unit came out and asked me why the Rhodos on the left were struggling so much. After all, the entire row was planted at the same time.
Good question! So let’s have some fun. Study the photo and then see how many different ideas you can generate that could potentially explain this mystery.
Ready? Below are my own ideas and you are always welcome to post your own comments with this blog post.
- As a certified arborist I immediately considered competition between tree roots and Rhododendron roots. Considering the size of the tree, I suspect it’s a huge drain on available resources. That could easily explain why the specimens closest to the tree are struggling.
Related to this is shading. It’s distinctly possible that right after landscape installation the Rhodos nearby received more shade than the ones on the right. Shade means less sunlight and therefore less food production and growth.
2. Sticking with the tree a bit longer, I also checked on allelopathy. Allelopathy refers to “chemical modification of a site to facilitate better tree growth and to control ecological volume and essential resources”. Basically the tree uses chemicals to tell neighbouring plants that they’re not welcome.
Gleditsia triacanthos exhibits moderate allelopathy through roots. Bingo! No wonder the Rhododendrons are struggling.
3. The owners have a dog and it’s possible that little Fifi urinates right by the door which would affect the soil closest to the Rhodos on the left.
4. The Rhodos on the left are also closer to a roadway corner which means there is a higher chance (larger surface area) of strong reflected heat hitting the Rhodos on the left.
5. Finally, about half-way on the wall is a vent and I noticed debris on top of the soil similar to lint that accumulates in my own drier. It’s possible water carries chemical residues down slope to the left. That would be one extra problem for the specimens on the left.
Conclusion
This case nicely shows how much landscape professionals need to know in order to answer client’s questions. The lady approached me and I had to think quickly. Fertilizer? Sure, it can’t hurt as long as she applies it to the drip line.
After she disappeared into her unit I started thinking about my list above. What do you think is the problem here?
