I just spent 50 minutes on Garden 6, its my fifth spectre. Usually on my fifth run, I try to collect all the seeds. I have been successful at this for the past 5 Gardens. Garden 6 is the relatively easier garden in the new field (Garden 6, 7 and 8), and garden 7 has given me problems with two spectres already (i'd imagine how frustrating it'd be to find all the seeds).
So, Garden 6 was a breeze, and collected all seeds in about 30 minutes (note, I was playing leisurely and fooling around with my buds). Well, all except one. It says 26 seeds out of 27. Now I'm tearing my hair out, I jumped to every nick and cranny blasting pollen everywhere and none seems to fly about. I don't know where this seed is. In the end, I ate nearly all the crystals so I had to just call it quits. Agh, I spent 50 (expletive) minutes on NOTHING!
Ouch, I know the feeling, that can be quite frusterating. One of the older archived topics has maps of 6-10, so you might check those to see where the missing seed is. And yes all seeds on 7 is very annoying.
In garden six there is a hidden seed close to the ground on the far right.