Blaiyze

G'day folks! I'm very new to VS, so please bear with my derpiness. I've picked up some tree seeds and want to replant so I don't completely deforest my game, but uh...yeah. I can't figure it out? I have the seed in hand, and right click soil and nada enchilada. I've tried planting it on tilled soil as well to no effect. The handbook mentions saplings but I've literally never come across a sapling, just seeds. So...how the heck do I plant these suckers and grow trees?