First time trying a plant deck...

So here goes :


remember its my first time trying this.....

With only 10 Plants, you can't seriously run 3 copies of Mark of the Rose. Lord Poison belongs at 3 (as does Tytanial imo, but you can keep her at 2 if you want). Shrink is random here, and Book of Moon is not as useful in this deck as it is for some other decks, unless you plan on taking out Black Garden (which I would suggest because Black Garden really needs the deck to be built around it). Compulsory Evacuation Device is really an overreaction to Stardust Dragon. CED is, and will always be, a -1. You can take out Stardust easily with Tytannial or Gale or almost any synchro, so I'm gonna say ditch it. The deck needs Pot of Avarice so you can re-use cards like Lord Poison and Lonefire Blossom. The Extra Deck is missing Queen of Thorns. I'd also suggest adding in Ryko and/or Lyla to the deck to give you more control cards and a way to load your graveyard for Lord Poison, PSZ, Miracle Fertilizer, Mark of the Rose, and Pot of Avarice.

After taking up fixes i end up with 20 monsters...isnt that too much for a plant deck?

Nah, especially if you're running Pot of Avarice 20 monsters is actually right in the middle of where you should be (I say 17 is bare minimum and 22 is about maximum for Plants).