After years of being under a deck, garden plants have decided to regrow and are coming up along the edges, and also through the deck slats, I had started to remove them as they came through, but after a couple of months of being ignored, they have become prolific, and I even spy a sago palm and for sure don't want that to get robust. Any ideas on how to rid my deck of these volunteers ?

BurnOut is a less-toxic herbicide that might work. It works on contact only (doesn't kill the roots), and may need repeated applications until the plant gives up.
If you want to nuke them--go with glyphosate (Roundup), but I'd try the BurnOut for a season first.