Here are a few plants that are bad for dogs (keep in mind that this may not be all of them). Consider removing them before you adopt a dog, especially when they are in your backyard.  Research the effect of any plant before buying it.

• Castor bean or castor oil plant (Ricinus communis)
• Cyclamen (Cylamen spp.)
• Dumbcane (Dieffenbachia)
• Hemlock (Conium maculatum)
• English Ivy, both leaves and berries (Hedera helix)
• Mistletoe (Viscum album)
• Oleander (Nerium oleander)
• Thorn apple or jimsonweed 
• Sago Palm Plant (Cycus revoluta)

Sources:

Poisonous Plants for Dogs | PetMD 
Poisonous Plants for Dogs – American Kennel Club (akc.org)