Question
Dear Mr. Hyland,

My question pertains to pin oak roots and nearby planted flowers:  Do pin oak roots emit a chemical that keeps other plants from growing?  About 10 years ago there was no problem, the tree was much smaller and the flowerbed was spectacular.  Because the area around the tree is a high foot-traffic area and grass wouldn't grow, I laid a thick cover of coarse chips for 6 feet around the base of the tree.  It's growth really took off, adding about 15 feet to the tree height.  Then, starting about 4 years ago, the flower demise was limited to the corner of the flowerbed closest to the tree, regardless of what type of flowers I planted.  I found many smaller (less than 1/2 inch in diameter) pin oak roots there.  This year almost the entire flowerbed is affected. Is it just coincidence that there are also pin oak roots throughout the flowerbed? There is no evidence of insect infestation, and of course I am keeping the bed watered.  I'm happy to report that the pin oak looks great.  But, can the pin oak roots be committing chemical warfare to maintain its turf?  If so, is there a tree-friendly solution?  I really like the tree.

Answer
No the roots do not contain a chemical that would stop under story growth. The roots a small and shallow. That leaves little soil for plant to grow. especially if the plant needs a good root system. I think it is a combination of too little soil for the plants , shade of the tree for sun loving plants and the tree roots will take up most of the moisture from the soil. Now there my be some chemical reaction to the type of chips used as mulch. Some will increase the acid and many flowering plants do not take to soil with high acid content. Check with your local nursery about flowering plants that grow in the shade and grow in acid type soil. But when you plant them make sure you do not damage the roots of the tree or add more than 3 inches of soil to the area around the tree.