Question: Is it true that pecans will keep other plants from growing beneath them? Is there anything I can do to counteract it?

Answer: That’s a physiological process known as “allelopathy.” Some plants do retard the growth of other plants nearby, although much remains to be learned about this phenomenon. To the point, it needn’t be much of a problem with your pecans. If you amend the planting soil carefully prior to putting shrubs, groundcovers and flowers under the pecans, they should do fine. The amount of shade a large pecan casts is actually much more damaging to the plants underneath, unless, of course, they’re shade-loving types.