To summarise, I extracted a normal looking mature rose embryo from an Iceberg OP red hip.
The embryo was immediately placed in a jar containing a 10% X (full strength 15N/4P/26K) fertilizer solution. This jar was then placed in a dark cupboard, hoping for a sprouting to occur.
The reasoning behind this trial was to see if the relative lack of visible+UV light energy might act as an extra stimulant to rootlet formation in those embryos which fail to root in full light environments (a phenomenon sometimes coined as “radicle blunting”). I also replaced the usual tap water with a very diluted fertilizer solution as the germination medium, hoping that it may complement the darkness by acting as a separate stimulant to rootlet formation (as well as overall seedling growth).
When the embryo commenced to sprout at the radicle end in the dark liquid environment (around day 7), it was then transferred out of solution, and sowed into a pot containing seed raising mix and allowed to germinate, exactly as if it were a rose achene/seed. Whilst in the pot, it received once daily applications of the same diluted fertilizer solution.
Here it is as a fully developed seedling, this morning, pulled out of its potting mix:
For now, I am encouraged by this single result to continue this dilute fertilizer + darkness regime on any subsequent embryo work I do, unless any negatives show up.