I've had my tomatoes outside in approx 30cm pots for 6 weeks now. Notwithstanding a magnesium deficiency, I believe I have successfully treated with epsom salt, they seem to have been fine.
Over the last couple of weeks the lower leaves on a couple of the plants have first gradually gone completely yellow, then turn to brown and started to wither away. It starts at the leaves on the very bottom stems and gradually moves upwards. The upper leaves and fruit of the plant seem to be fine although I have noticed growth has slowed significantly.
I initially suspected overwatering, however I've reduced the watering frequency and it's made no difference.
I'm in the UK. Any pointers appreciated!