The timing of flushing depends on specific circumstances, but there are three main instances when flushing may be necessary. Firstly, it is common to flush weed plants before harvest to ensure the harvested buds are free from excess nutrients, resulting in a cleaner and smoother smoke. Secondly, flushing is recommended when transitioning from the vegetative to the flowering stage of growth. Lastly, if your cannabis plants experience nutrient lockout, flushing can help restore balance and proper nutrient absorption.