You might find it easier to add to the individual pot as it is not always
easy to mix it evenly through a full bag of compost.

If you are keeping your plants outside then it is a bit early to add the
fertilizer though if the plants are inside then go ahead.
Also depends on the life of the fertilizer, as slow release comes in forms
from 4 months to 2 years

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk