You might be able to give it enough hours of light but is it enough lumens for a sunflower? I dont know how much lumens they would need but i'd imagine its loads? There's also no wind indoors so the stem would be very thin and weak unless you have a fan blowing against it! I think they can be cut back, i have read you can pinch out sunflower so maybe that is something to consider! I have had an earthwalker throw out a few long/tall branches after slugs ate through the main stem! if it just sprouted now naturally it would not survive so I guess there's no harm in trying
