YELLOWING USUALLY INDICATES TOO MUCH WATER...DOESNT IT? THEY SAY TO STICK YOUR FINGER IN THE SOIL TO 3 INCHES,,,IF MOIST ITS OK AND THEN WHEN YOU DO WATER IN THE POT WATER UNTIL IT COMES OUT DRAIN HOLES,,,IVE KEPT MY SEEDLINGS OUT OF THE HOT DIRECT SUN,,,(HERE IS PHILIPPINES) HEAT IS TOO MUCH WHEN YOUNG,,GOING TO TRANSPLANT TO GROUND ONCE LARGER,,THEY DO WELL IN MOST ALL DRAINED SOIL...THATS ALL I KNOW BUT GOING TO TRIAL AND ERROR,,,OH IF YOU HAVE DOGS AROUND,,,PROTECT,,,NOTHING WORSE FOR ANY PLANT!!!,

if there is a way you can enclose a space around them to provide both heat and humidity - indoor air tends to be very dry for plants with a central heater on.

Allowing more root space will also help.

Ignore what was said previously by others. Your plants are doing fine. Yellow bottom leaves are old leaves that the plant will discard because they are becoming useless. This is normal. Yellow new leaves are normal. They will turn green.

If there are any leaves in between the new and old leaves that are yellow, then that means you need to fertilize. Still, your plants will be fine.