Are you soil or hydro?
I don't hydro so can only offer soil info.
If soil what kind? does it have nutes in it or did you use a seed starter?
I use a seed starter and after 2 weeks would be a good time to start 1/4 strength nutes.
If pre mix soil it may have enough nutes to take you about 1 month but I would suggest to start
nutes at 1/4 strength around week 3 anyway.
What size pot? If in a solo cup start thinking of up potting to about 1 gal. Bound roots can cause
some symptoms that would lead you on a wild nute chase.
Good luck