nice little plant you got there mate....however to get some benifit out her/him you need to get it under some kinda light envirolights are cheap at the mo then extraction/intake/mylar gees is it worth it lol you say the plants 5 week old it should be waste height by now and showing its sex....im not into outdoor growing but best chance i rekon is if you can repot it and whack it outside you may be rewarded! and let the big lamp in the sky do its job......whats the name of the strain is it indica/sativa based? and unfortunatly its illeagle to grow in the uk but ok to buy seeds and ok for the goverment to tax you 17 percent on any grow gear purchased (tossers) and id ditch the miricle grow mate canna in general dont get on with it,get a decent compost and bigger pot and as i said the outdoors is your best shot,heres a couple of pics that might help you to choose to be self suficient and grow your on weed....mine are 26 days into flower......best of luck anyways.

s.e.t theses are grape crush/mazar and very white the vw has 10 weeks to go and the other 2 around 6 weeks