What soil are they planted in? Looks like fertilizer burn. Do you have drainage holes for water to run out? Fertilizer salts can accumulate and burn leaf tips.

Also, you need to deadhead (cut or pinch off) all those dead flowers so the plants will continue to produce more flowers. Your plants aren't dying. Just rinse the soil and pinch.

I didn't fertilize them until a week ago (the pic was taken about a month ago) they r doing fine now.
can I replant the seeds?