DougL said:For containers, and especially seedlings, you need to fertilize at half strength or less.
Now, compost won't work well in a container as a fertilizer. First of all, it's a VERY mild fertilizer, and even in the ground it's a VERY slow fertilizer. Containers don't have anywhere near the bacterial population that you need to break down organic fertilizers of any kind. So they kinda just sit there.
If this is fertilizer burn, you need to flush the mix with water. The stuff will leach effectively. Yeah, it'll get really wet. But let it drain, and it'll be fine.