why wont the plants grow well?

Hey all,
There are 5 plants growing in an aerogarden classic. One plant is about 5 weeks old, the other is 3 weeks old, and the last 3 are about 1 week old. the 5 week old sour d is still about 4 inches tall and has 4 nodes. Why is this? all the plants i see online look like they are so big and grow so fast but mine seem growing slowly. can someone tell me what to do start to finish please? Thanks!

pics could help diagnose, what is your light schedule, temps, ph, what nutes. 4 inches with 4 nodes ain't bad that is some tight node spacing. I have never grown that strain so i wont be much help but the more info you provide the better the differential we can provide.