Stalks

hey just wondering if anyone has some info on weird situation.

iv a few plants on an outdoor grow and the stalks on them are twice as thick on the top as they are on the bottom. bit strange as iv only ever encountered it the other way round.
just wondering if anyone has heard of it before and is there anything to worry about or whats causing it.

how old/high are they? Maybe they got too much stretch early on,do they have plenty of sunlight at their current spot? have a look at tomato cages to hold them up and secure branches, what strains have you out?

yeah loads of light and they can hold themselves up, they're about 16 inches tall, they were planted two months ago, all are fresian dew. iv never tried this strain before. it doesnt seem to be causing any problems, its just a bit bizarre