Question: Can I discard spent coffee grounds in my houseplant pots?

T. Dominguez, Santa Fe

Answer: Sure you can, but I don’t exactly recommend it. Putting the grounds directly on houseplant soil might not pose a problem, but it’s hard to be sure. Research on the composition and chemistry of coffee grounds has shown wide variability. Some of this variability stems from differences between species in the Coffea genus grown for commercial production — most commonly either Coffea arabica or Coffea canephora (syn. C. robusta). And then there are many varieties and cultivars too. Plus, the darkness of the roast affects the grounds’ pH, with lighter roasts tending to be more acidic, but not uniformly so … more on this later.

While it is hard to find published research results on…