What is a half-hardy perennial? How do I grow them?

Half hardy perennials are plants which will last for many years, providing that you give them protection from the cold in winter.
Most half hardy perennials are used for normal summer bedding plants – geraniums (Pelargoniums) Busy Lizzies (Impatiens) and Dahlias are just a few!
Begonias and dahlias will live for several years if they are protected from cold conditions. The dahlias die down, but will come back from their tubers providing they are kept frost-free.

Some plants can be fully hardy in milder areas, but it is better to protect half hardy perennials if you want to be sure of success.

Impatiens or Busy Lizies are typical half hardy perennials

Half hardy perennial Impatiens - Busy Lizzy - has to be sown in heated conditions then hardened off before planting out after the spring frosts.