In the case of dogs eating garden plants and bulbs, the risks range from vomiting and diarrhea to seizures, and death. Here are the plants and bulbs to avoid:
Spring crocuses are attractive to many dogs. Ingestion can cause vomiting and diarrhea leading to dehydration.
All parts (flower, plant, and especially the bulb) contain poisonous alkaloids with potential to cause excessive salivation, vomiting, diarrhea, convulsions, and heart problems.
All parts, and especially the bulb cause vomiting, diarrhea, sometimes with blood, depression and tremors.
Toxicity is based on the type of lily. The calla lily, amaryllis, lily of the valley are all deemed dangerous to dogs by the ASPCA. Clinical signs: intense irritation of the mouth, tongue and lips, excessive drooling, vomiting, difficulty swallowing.
All parts, specially the bulb, cause hypersalivation, and the same reactions as hyacinths.
BOTH tulips and hyacinths are more likely to be ingested in larger amounts than many other bulbs since they often come in bags of bubs, so dogs have access to a greater volume of them.
There is also a good list with pictures of plants that are toxic, or safe to have in the home, and/or garden for companion animals.