My current grow, I transplanted and backfilled support when they were 3 to 3.5 inches tall. They stretched some more and got another 1" to 1.5" of fill support. And with all that, I still have 3 or 4 plants (out of 18) that need some form of support to keep them off of the ground.
The following link doesn’t necessarily relate to the great outdoors, but it might be useful