Any time, you first add nutes/ferts to young plants....
add them in 1/4 strength....use 1/4 for a week,
then use 1/2 strength the second week if no problems come from the first week....
And so on... let your plants talk to you ... let them tell you what to do...
Because they are smaller, they also will not take up as much water as a full grown plant...
As they grow, you will add more and more until full strength...
Good Luck...