Personally, I'm not a big fan of the thallids, but if they work well in your deck, keep them. I would suggest putting at least one more Overwhelm in your deck. Also, if your saproling deck is based on having a ton of creatures, try Conclave's Blessing, Scion of the Wild, and Life and Limb. They only problem with Life and Limb is if all creatures are destroyed, all your forest are gone. But other than that, this is a pretty good looking deck.
When something dies, all things benefit. Well okay, just our things."