Okay, two things which you may consider... Firstly most potting mixes (including Black Gold) contain a significant proportion of sphagnum peat moss. With sphagnum once it dries out completely it becomes kind of a bitch to get it moistened up again (it becomes hydrophobic). A lot of the time this has already been remedied, in part, by the manufacturers addition of a wetting agent (such as yucca extract) which prevents the water from beading up on the surface and aids in the absorption. It always helps to wet your soil\medium down prior to planting anything in it. I use a hand-pump pressure sprayer for this but you could also use a regular spray bottle.
Second thing is that in this mix there appears to be earthworm castings, forest humus and compost. Earthworm castings and compost are themselves forms of 'humus' or mostly stable\thoroughly decayed organic matter (detritus). These are all awesome ingredients that impart unique blends of nutrients and micro-organisms to the medium, and humus is also responsible for holding water as well as retaining major nutrients; but too much without correction for soil texture\drainage isn't ideal. There should be pumice and perlite in there but obviously I can't see\feel your mix to gauge if it is what I would consider to be properly blended by itself.
When I mix my own stuff up now I do a simple 'test run' watering in a container with just the medium. I pre-moisten the mix as described above, fill up a random planter with it and then water it good. Run-off should occur in well under a minute.
