AusBonsai

ive been growing these seedling for a month, and i want to know when i cant start to fertilize them. i know there still young so its probably not going to happen anytime soon but when should i start? all of them have got there first true leaves about a week ago. could i give them some thrive shake 'n' feed slow release fert it has nkp of
N11 K3 P8 should i give it some and see how they go?

also i have 2 little apple trees seedlings, ive had them for about 3 months now when can i start to feed them?

Baz,
Red gum love fert. They do not seem sensitive to P so you can give them any fert you would give to any other tree.
I'd be fertilising lightly now to keep them growing.
This is the stage when I usually prick out seedlings into individual pots to give them a bit of room to grow. Mine have not objected to pruning the main root when pricking out seedlings like these and as for other species cutting the root at this stage will force more lateral roots.