Struggling to Keep My Plant Growth Experiment Consistent

[tomcowell]

Hi everyone,
I'm a college student taking an introductory biology lab, and my current project is looking at how different LED light colors affect basil seedling growth over four weeks.
I thought this would be pretty straightforward, but I'm running into a problem. Even though I'm using the same pots, soil, watering schedule, and light duration, a few of the seedlings grew much faster than the others in the same group. Now I'm not sure if it's just natural variation between seeds or if I'm missing a variable that I should be controlling.
At this point, should I start over with a larger sample size, or is this kind of variation expected and something I should discuss in my analysis instead? I'd love to hear how others have handled this in their own experiments.
FNF