your plants look good.. they are definitley not getting all the nutrients that they could be getting.. either not enough nutrients in the soil or the PH isn't right.. but the plant/s looks good and stable..

Lower leaves turn yellow and die for a variety of reasons.. most of which are not worth dealing with.. most common is the leaf is just not getting enough light.. to many leaves covering it...

look into a thick bush... a bush outside, under the sun,...

it can be 5 feet thick, but only the outer one inch is green and leafy.. if you look into the bush it is dark and nothing but a bunch of sticks.. no light, no love, no growth...

to fully assess your plant I need a wider shot and a shot of the stem.. is the stem red at all?

smb

: )

and now you KNOW!!!!!