Another Plant Question! 'Terrestrial' Fertilisers?

Bit of a random one this, but I'm currently running a small QT which isn't actually quarantining anything at the moment. I don't really want to leave it running for no reason (missus will be onto me about the electric usage!) but equally I don't want to pack it all away.

My thought is to use it to try and propagate some of my plants outside of my main tank. The idea being that they can grow to a decent size without any unwanted fishy attention before I then return them to the main tank. I'm particularly thinking about my Java Ferns which are sprouting quite a few new leaves at the moment.

What I'm wondering (finally got to the point!) is whether I could utilise a 'terrestrial' soluble fertiliser to help them along seeing as they'll be no fish in there? I have some Miracle Gro All Purpose in mind which looks to have a 24-8-16 NPK ratio. I know the high Nitrogen and relatively high Phosphorus wouldn't be good with the fish, particularly as there's ammoniacal nitrogen in there as well, but will it matter in an empty tank?? I'd perhaps expect an algae bloom but this wouldn't really be a problem in that tank. 

Good suggestion - I know I commented on your post about the Walstad method a bit back but it never crossed my mind to try it with my QT tank.

Just a couple of queries; Would this still work with Java Fern as I understand they draw their nutrients straight from the water column (i.e. do beneficial nutrients still leach up from the soil)? Do you think it would do any harm turning off the filter (or only putting it on periodically) and also heater (or turning the heater right down to <20c) with it just being plants?

Cheers

I think I'll give it a try......

I have seen some good videos on youtube regarding this method, have a look at  http://www.youtube.com/user/Dustinsfishtanks

He's a bit nuts! Some good videos though.