Just the top of stem is ready, why and why just top half?

[BornTo420]

I searched here and found info on red stem but I only have a red on the top edge only. They just received their first full dose of Bloom nutrients @ 975 ppm & 5.8 ph. The temperatures outdoors have been ranging from 80 highs to 65 days, to 69 to 50 degrees at night.

Hope the picture helps.

 

[GodSpeed]

That isnt anything to worry about BT420 some strains show red in there genetics also if the stems are holding weight like a big leaf these stems tent to go a redish color.

Time to start worrying if your stems start to look like this.