Do you ever have plants that don't do well? That seem limp, flat and lifeless, or fail to grow? You wonder if it's a deficiency: not enough nitrogen, not enough sunlight, not enough water. But, perhaps it's not a deficiency at all. Perhaps something is in excess, like aphids, or mealy bugs, or scale . For example, you may have an excess of cats' bottoms in your plant pots.
[This has been tagged under wildlife, but this is Cally, MIL's cat, and she's not really wild, just grumpy.]