I've never heard of root-boosting as a method to lengthen the roots; I always use it as a pre-flowering nutrition boost to improve yield size and color.
A week before you change the lighting hours before you plan on pushing the plant into flowering phase, uncover the roots with your hands (this only works with soil and unfortunately not hydroponically) and pour 1-3 cups of pure, unpolluted water ( I use spring - don't use distilled as there are traces of nitrites in it and will throw off your nutrition feed.
Wrap banana peels around the roots loosely and recover the roots. Do not add additional water to the top of the soil for a day or two. When you change the lighting to induce flowering, the peels will have already begun to decompose and will release bursts of potassium and beneficial vitamins during flower, resulting in higher yield. The plants are also much brighter in color.
To help with your question, if you use soil, place your seeds in the ground deeper than normal. The extra weight will strengthen the roots and stem, and be less likely to bend or break in it's future.
Picked my fucking brain, hope this helps,
MaryJane