Trimming onion seedlings
I notice a lot of people recommend trimming onion top seedlings. I planted two flats about 3 weeks ago one NY Early and the other Red Bulb. Right now the tallest ones are about 7 inches. Not sure how much taller they will get indoors but it doesn't seem they are bothered by growing into the lamps or falling over a bit.. The bulbs are old school T12 cool whites and also 2 40 watt CFLs.
I've read people's opinions saying that trimming promotes stronger roots and thicker stems but have yet to find a single incident of anyone doing a side by side study.
How necessary is trimming onions? And what is the science behind it?