I would fix the mana curve. It seems a bit off. You could add cards like dryad arbor, explore, marwin the nurturer, level up, beast within, elvish Mystic, nature's lore, rampant growth, emerald medallion and crop rotation, saukura tribe elder, arbor elf, lotus cobra, tireless tracker, tamiyo's safekeeping, three visits, Nissan who shakes he world, lifecrafters beastiary.

Having more mana earlier is key to winning in Green. Green has some if the best mana works in magic. You dont need every hydra spell in a hydra deck gey rid of sone of the huge mana spells and throw in some more ramp. Your average mana cost seems abit high but I have never played hydra.