To overwinter spring bulbs in pots outdoors, give them good drainage and protection suited to your winter climate; insulation alone may not protect roots during prolonged deep freezes.
Essential Concepts
Keep bulbs cold, not waterlogged; bury pots or use an unheated garage in severe winters.
Related posts:
Growing bulbs: https://www.rhs.org.uk/bulbs
Growing tulips: https://www.rhs.org.uk/plants/tulips/growing-guide
