What is the cause of Seedling stretch?

[Madbud]

Seemed like a good time for a discussion on seedlings that sprout like spaghetti. I start seeds in solo cups of soil after they sink sink in water. Nearly 100% germination and i learned a long time ago if it stretches 3 inches, add 2 inches more soil, problem solved. But what causes the stretch? Light too dim or too far away, lack of airflow? Like to hear some science and bro science(and a big NO to paper towels).

 

[MEGA956]

Maybe a mix of environment and genetics? Do hemp seeds do the same thing?

 

[Cirroji]

i always assumed more stretch = them trying to naturally get to an area with better lighting aka closer to the "sun"

 

[BigBlonde]

But what causes the stretch?

A light intensity that is too low is probably the most common cause.

 

[steamroller]

Too much water.

 

[Madbud]

So do you get stretch? If not for adding soil as support, mine would fall over.

 

[TSD]

I always assumed it was lighting. I'd honestly rather have a little stretch than a plant that stays short and squat and all the leaves are right near the dirt... extra stalk isn't a bad thing if you're training either.

 

[Madbud]

I lowered the light on these. The middle pair sprouted yesterday, the other 4 this morning. Its a 150w led at about 25% and now about 28” to see if the others stay short. Small overhead fan too. The other snapshot shows a soda bottle dome on a helmet head that needed a little more humidity.

 

[TSD]

Mine stretched too cause I used a t5 and had it too high, I added a bit of soil to a few, trying to strengthen the stalks with the fan. I added a bit of soil to a few, and if they still look lanky when it's transplant time, I'll bury them a bit extra. All my lower shit gets stripped and I'm outside anyway, so a little stretch isn't a huge deal.

 

[Madbud]

I started with flourescent shop lights many moons ago because they can be within an inch or two. Frankly i like them better than led, bigger leaves, but its a hassle switching lights now.

 

[steamroller]

If light can be set lower power then go even lower and then lower the light physically even more.
I start under low power aquarium LEDS and keep the light pretty close. Less than 8 inches for first week.
Do you have IR to check leaf temperature? Just make sure they don't cook.

 

[Madbud]

Yeah, thats an idea, i have an ir thermometer!

 

[quirk]

In low light conditions, a hormone is released that stimulates rapid stem cell elongation in an attempt to get the light it requires. While this is taking place, root development is minimal.

 

[Madbud]

Recalling something about moon phases for planting root or stem type plants too.

 

[Madbud]

So both my ambient room temp and soil temp is low 80’s F. Just wait a couple days to see if lowering the light has an effect on the stretch.