Question
Some of my established,previously happy potted plants have developed dull leaves: meyer lemon tree(in full sun) and an acanthus (in mostly shade.)  What do they need? Thank you.

Answer
My first thought about the lemon is that it is probably aphids. Look closely at the leaves. If you see sticky residue, or little spots, or ants, it is aphids. In that case, wash the plant with soapy water. Then when it drys, spray with Safersoap insecticide.
If it is not aphids, washing the plants would still be a good idea, to get the dust off of the leaves.
Another way to have healthy leaves is to spray them once a month with liquid kelp.
Fertilize with 20-20-20 when the temperature is below 95 degrees once or twice a month during the growing season.
Watch the water amount closely. Try not to get water on the leaves, except when you are washing them.
bakerplanter