How to Find Your Last Frost Date
And why it matters… or does it?
We hear a lot about first and last frost dates.
But what are they?
And do they really matter to the average gardener?
Well, the answers may surprise you. As with lots of gardening guidelines, first and last frost dates are more important for some gardeners than for others. So, let’s take a dive into when and how your last frost date can make a difference in your gardening.
As you are planning for your spring planting, there's one really important date to mark on your calendar: your average last frost date.
What is a last frost date?
Your average last frost date is the last day ON AVERAGE that a nightly low temperature reaches 29-32 ℉.
Where can I find my average last frost date?
These averages are determined by zip code, and you can easily look it up when you start planning. I use the NOAA website which has an easy interface to reseach by zipcode.
But remember it is an AVERAGE. For example, in the Denver area, the historical average last frost date is May 11. But in actuality, that date could be as early as April 5 and as late as June 8 – and has been in the last few decades.
As the climate changes, however, those last frost dates are changing. While our historical average is May 11, the average for the last ten years is May 5 – and that's the date I generally use.
So, in practical terms, what does a last frost date mean for gardeners?
It's a date to use as you are planning seed starting. Looking at your seed packets, count back from your last frost date the number of weeks prescribed to know when to start your seeds. And it is the first date that you can think about planting out tender plants.
But I always have some frost protection around just in case! We will talk more about that soon. For now, mark your last frost date down on your calendar. The time will pass quicker than you think!
Last Frost Date FAQs
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The average changes over time, and climate change contributes to these changes. But your average last frost date is just a guideline for planning your garden. Keep in mind that sudden cold snaps can still happen after the average last frost date.
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If a late frost is predicted, take steps to protect your plants, such as covering them with frost cloths, blankets, or row covers. You can also move potted plants indoors temporarily. This helps minimize damage to sensitive plants and gives them a better chance to thrive.
For more on last spring frost protection, check out this video.
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While some cold-hardy plants like certain vegetables or flowers can be planted before the last frost date, tender plants (like tomatoes and peppers) should wait until after the frost risk has passed. If you’re eager to plant early, consider starting seeds indoors or using cold frames to extend your growing season.
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Frost-sensitive plants typically include most annuals, warm-season vegetables, and tropical plants. These plants require warmer temperatures to thrive and can be damaged or killed by frost. Check seed packets or plant tags for frost tolerance information.