Cuphea plant leaves turning brown

[carmeljacques]

Last spring I purchased a cuphea plant and planted it in a large redwood planter in a partially shaded spot on my deck. Since then it has developed lots of new growth along the existing stems and some new stems as well. Recently, however, a lot of the leaves have started to turn brown/grey from the tip of the leaf back. Does anyone know why this is happening? Am I over/under watering (I use a moisture meter and try to keep the plant moist but not wet) or is this normal at this time of the year? There is no indication of any insect infestation.

[lillgardnr]

with browning leaves you should check the ph level of the soil. have you used fert.?

[carmeljacques]

I did fertilize using Grow Power Plus which has some added acid (2 % humic acid - used in our area to dissolve the chalk rock which underlies all our gardens). Is it likely that this makes the soil too acidic?