The onions that I sowed a few weeks are growing really well. I’ve heard that onions (and other alliums) are “heavy feeders,” so they benefit from a good amount of fertilizer.
In general, from what I understand about fertilizing seedlings, seedlings get the nutrients that they need from their seed for the first few weeks of growth, but once they have a couple of true leaves (not cotyledons), you can add fertilizer, but only very weak strength fertilizer as you don’t want to burn the roots.
Yesterday was the first application of fertilizer. I used very weak fertilizer – a few granules of MiracleGro in a half gallon of water. I’m nervous about burning the roots and I’d rather err on the side of too little than too much.
Another thing I’ve read about onions is that you can trim them (kind of like grass) while they’re growing indoors to keep them from getting too leggy. They say to keep them at about three inches tall. The tallest of my onions are right at three inches, so I think I’ll wait another week before giving them a haircut.
It was good to bring them upstairs in normal light because I didn’t realize the pots were growing algae! I couldn’t see the green under the purple LED grow lights. I clearly have been watering too much.