Which bulbs can I plant outside?
Since spring-flowering bulbs can easily withstand even a fairly harsh winter, almost all of them can be planted outside. They even need a cold period in order to flower. The exceptions are hippeastrum (amaryllis) varieties and narcissus “paperwhite”. ...FAQ
Depth of planting
A basic rule is to plant at least twice as deep as the height of the bulb with a minimum depth of 2 inches or about 5 cm. Too shallow planting leads to poor, incomplete root development and short scrawny plants. Shallow planting also increases the risk of frost damage. Planting too deeply increases the chances of the bulb rotting and also weakens the growth considerably as it pushes upwards