My seedling has been above the soil for a little over 48 hrs. It has grown to 2.5" tall and has 4 small leaves. How high should I expect it to grow before the next set of leaves?
It depends on light intensity. Mine usually have their third set by 2 1/2" tall. Insufficient light causes plants to stretch.
The general consensus is that seedlings need very little light. I have my HLG 260 turned all the way down running 18/6. Should I turn up the light if my plant doesn’t grow a third set of leaves by 3 to 4"? Thanks.
Spectrum and intensity both. If you for example have lights in 5,000K you might see more stretch. My custom lights are 3,000K about 18" off young plants and turned down to around 125 watts.
Compared to a flowering adult plant, sure. But they still have to have spectrum and intensity otherwise you will get what you are experiencing now. Normally my first set of leaves is so tight to the ground it’s hard to get water in there.
So the HLG 260 rspec is supposed to have a full spectrum of light. I am currently at 24" above the top of the pot so around 21.5" from top of seedling. I asked in another post if too much light is harmful to seedlings and didn’t get an answer.
Too much is harmful but these QB’s are a bit more ‘diffuse’ light: it’s not concentrated like other light technology. This actually allows for great canopy penetration when lights are tuned correctly you can SLAM them over a flowering plant–like 6" or so—for light into canopy. You don’t have to be 3 feet above plants to get coverage that you have to do with more point-source light (MH/HPS, LEC, China blurples etc)
The Rspec has some additional red for flowering but will do fine from seed to jar.
This was true for my first ever, still in veg atm, and there finally growing up a little bit taller and the nodes are spacing a little better
Also can depend on strain. Most of my sprouts (indica dom) stay low and wide but some Gorilla Glue seeds I’m growing right now are stretching more than usual.