You are in zone 5a. The average last frost date is between May 1-10.
These dates are guidelines and you will need to watch the weather trends.
When your seedlings have generally reached 3 to 4 inches in height and an established root systems.
Bulbs can be directly placed in the garden in the Spring.
Remember that all seedlings and plants need to be hardened off before planting.
Here are some articles that will help you.