Sweet basil: Are dark green and slightly smaller leaves better?

Question

I planted some sweet basil seedlings into two different long planter pots and they come from the same batch of seedlings. They are at the same location and get the same amount of sunlight and water.

However, the soil in the pots is slightly different as I used different soil mixes. In one of them, the sweet basil plants are lush and the leaves are darker green but slightly smaller. In the other one, all the plants are a lighter shade of green though the leaves are a bit larger. I suspect this pot is lacking certain nutrients.

Is that correct? What should I add to it to make it healthier?

EDIT: Added the photo below. It doesn't seem that obvious from close but from afar the leaves on the left are noticeably darker and smaller.

Answer 1

The larger leaf on the right is healthy - the one on the left is smaller and curled, indicating a problem of some sort. Basil leaves can look like this for various reasons - primary causes are insufficient sunlight, too much or too little water, and infection with mildew or insects like aphids or scale.

Inspect the ones which look like this thoroughly - if you can't find any problem with mildew or insects,and they really are receiving enough sunlight (a slightly different position may mean they're not actually getting as many hours as your other plants) then it may be that the soil you used is either not retaining water long enough for the plants to take it up, or is poorly drained, resulting in too much water sitting at the root. More info here.