I got some Miracid 30-10-10 for my Garden Hydrangeas, would this be good for Citrus?

If you flush your containers on several occasions every year, before, during and after each growing season, then you're good to go with almost any fertilizer available... Washing the medium out is done in order to avoid salt build-up in the soil. Accumulated salts can do a great deal of damage to a tree.

Best,
Igor