Digitalis is poison if ingested. There are many garden plants that are poison, even some that are commonly used as food. Rhubarb leaves contain lethal amounts of oxalic acid. Peach pits contain amygdalin, which becomes cyanide in the digestive tract. Apple seeds also contain amygdalin. But the most poisonous risk found in many flower gardens is Ricin, or castor bean plants. The seeds, which are attractive, contain enough poison to kill an adult, and children should be warned or kept away from them. there is no antidote for ricin poisoning.
And on the subject of poison, most snail and slug bait contains metaldehyde, which is poison to all mammals as well as to slugs.