I can't help you with a closet grow as I haven't worked with that limited a space. But I've seen postings here in the past where they accomplished just what you're looking to do. Keep reading all the postings you can find.
grey1223 Reviewed by grey1223 on . First Grow - Loose ends need tying please: Hello all. Thank you for providing such ample knowledge to us new folks. Plan/Space: Closet: - Dimensions: 18" x 6' x 6.5' - Soil - Budget not a big issue - I want an effective system Goals: Rating: 5