Understanding USDA Hardiness Zones
Why they matter, why they don't.
If you’ve read through my guide on when to start winter sowing, you know that I’m a broken record when it comes to winter sowing within certain windows. While knowing your zone can be helpful when it comes to choosing which perennials to grow in your garden, understanding your climate and knowing your last frost date are where you want to primarily shift your focus when it comes to winter sowing.
What are USDA hardiness zones and what do they tell you?
The U.S. Department of Agriculture takes data from roughly a 30-year period to determine average extreme minimum temperatures across the US and then categorizes this data into 13 zones based on 10 degree differences.
One very specific piece of information this data provides is which plants are hardy to certain zones. In other words, knowing your zone helps you know which plants are perennial where you live, and are therefore most likely to thrive and overwinter. That is really the extent of the usefulness of zone awareness.
What this data doesn’t tell you are things like:
How many days you experience that minimum low temperature
What climate or region you are a part of
If you happen to be in a microclimate within your zone
How close you are to the other states within your zone
Your first and last frost date
How warm your winters are
How hot your summers are
Generalizations
With USDA hardiness zones, we are able to make some generalizations. These generalizations being:
Toward the lower end of the hardiness zones (toward zone 1), winters tend to be colder
Toward the higher end of the hardiness zones (toward zone 13), winters tend to be warmer
So what do zones have to do with winter sowing?
Apart from choosing your perennial seeds based on the intention of overwintering, zones are essentially irrelevant to winter sowing.
Winter sowing made simple:
There are two windows for winter sowing:
When the weather in your area becomes consistently cold
The weeks leading up to your last frost date
When the weather in your area becomes consistently cold
This window is for anything requiring cold stratification (like native plants and perennials) followed by cool season vegetables, herbs, and hardy annuals.
This window extends to the start of the second window, and many seeds from this window can still continue to be winter sown at the start of the second window.
The weeks leading up to your last frost date
This window is for your tender annuals; anything that is frost sensitive—including seeds for your warm season vegetable and herb garden.
Were you helped by this? What questions do you still have about zones or when to start winter sowing? I’d love to hear!