Too much water on those fast draining mixes tends to leach out the nutrients; so you probably need to add fertilizer much more often.

Thanks John!

I've been using Fertilome 9-3-6 (slow release N). Do I need to change to something else in these circumstances?

I just acquired a jug of Osmocote Plus but haven't used it yet.

I would use a fast acting release fertilizer, one readily available to your plants as soon as your feed them while you wait for the slow release Osmocote to start breaking down or start to release some fertilizer after a few warm days of good weather and a few waterings......

Mike