Lots of things can cause a stretch, lighting, heat, genetics, and of course switching to flower.
I take it your talking specifically about the switch to flower though.
So yes plants will stretch in the 2 to maybe 3 weeks after the flip, indicas will stretch but not as much as sativas (they really stretch).
But you can prepare for it if your worried and it’s not to hard here is how:
- Take the total amount of vertical (height) growing space you have in inches/cm.
- Take the total from #1, and subtract the height of your lights when it’s at its highest point.
- Next, subtract the height of the pot/container your plant will be in.
- Finally, subtract the amount of space you’ll need between your light and your plants.
- This varies depending on the lights; CFLs only need about 4", HIDs need 12+".
- When your plants height reaches half of the number you’re left with, initiate flowering!
Now that being said if your are scroging the general idea is to fill your net 75%, it will depend on strain due to genetics determine stretch alot Durring flip.