What is Vernalization - and Why it Matters in the Garden

You may have noticed that some plants will not bloom or produce unless they’ve experienced a cold winter or an extended cold treatment (such as in a fridge)? That’s thanks to a natural process called vernalization.

Vernalization is only necessary for certain plants which need a period of cold temperatures before they can flower or produce seed. This chill “wakes up” the plant’s internal clock, indicating that winter has passed and it’s safe to grow and bloom.

For example, biennials like foxglove, hollyhock, and sweet William, as well as many bulbs (like tulips and daffodils) and perennial vegetables (like garlic), rely on vernalization to trigger flowering. Without it, they may stay leafy and never bloom. This is why many of these are fall-planted, to ensure they receive a cold treatment to encourage blooming.

In Saskatchewan's Zone 3 climate, this cold period happens naturally outdoors, but if you start seeds indoors, you may need to mimic it. You can do this by placing seeds or bulbs in a cool, moist environment—like your fridge—for several weeks before planting.

Understanding vernalization helps you plan better for spring blooms and successful harvests. A little chill now means beautiful colour later!