During flowering light height will depend on the strain you are growing and light you are using x square metre grow space but during flowering roughly 36 40cm from canopy is a good benchmark. We recommend this product for a pre-emergent application at the time of seeding. You ll want to separate and dispose of any male plants. Source: [url=https://cs.astronomy.com/members/sigurd-reichert/default.aspx]https://cs.astronomy.com/members/sigurd-reichert/default.aspx[/url]