When planning your vegetable garden and other gardening tasks – you need to look at both “First Frost” and “Last Frost” data for your area.

Cover image is frost on a sage plant.  Some plants can take frost – some can’t.

Which Garden Tasks go by Last Frost Date?

Last frost date tells you when you can safely put your tender young seedlings into the ground. You can’t just walk away though – gotta cover them in case of cold snap.  Note that these dates are only average.

Vegetable seeds. You need to wait until the soil is warm enough for the species. Last frost is only a guide. Sunflowers don’t mind cool soils but Malabar spinach does. I traditionally plant my sunflower seeds on Last Frost day. It’s a kind of celebration.

Prune Frost Damage. Last frost date means you can usually (I stress usually) prune any frost damage off plants like yellow bells that may have been nipped by the cold.

Other Pruning. Last frost date can also help with other pruning. Count back 8 to 10 weeks from the last frost date and that’s generally the ideal time to prune rose bushes, and winter dormant fruit trees like apples, peaches, and plums. In Low Desert – you can’t do that because there isn’t 8 weeks in some of our region!  So just pick the middle of the cold period to prune.

Succulents. If you have cold-tender succulents like the desert rose (Adenium) or elephants food (Portulacaria), you need to wait longer past this last frost date because they can be get damaged by cold below 45 degrees.

How Can You Predict the Future?

We can’t. All we can do is look at the past history (up to 200 years of it in some areas) and give an average.  Now despite all these years of historic data, farmers only use the last 30 years of data – because the world has been getting warmer (for whatever reason).  Best to use the average of the most relevant data.

Compiling Last Frost Data

Your donation dollars plus tax dollars at work! The numbers in the chart below are courtesy of the National Climatic Data Center (NCDC), National Oceanic and Atmospheric Administration (NOAA).  You can also find this plus your local area chill hours (critical for selecting fruit trees) and rainfall data on the United States Geologic Survey (USGS site) – but you gotta dig.

Best site for gardening frost data – AND in an easy to use format (just enter your zipcode) – the nonprofit National Gardening Bureau (NGB) has compiled them into a very useful frost database you can use to look up your area.  Feel free to join this lovely non-profit, and don’t forget to tell ’em I sent you.

So When is Last Frost?

The dates listed are normal averages for a light freeze (keep reading for definition). The possibility of a freeze occurring after the spring dates and before the fall dates is 50 percent. That’s a fifty/fifty chance folks.  Are you the betting sort?

These freeze/frost designations are categorized by their effect on plants that we typically grow in out gardens.

Light freeze – 32 F down to 29 F
Tender plants killed. Many tropicals damaged. Citrus ripening may get damaged inside the skin. Little destructive effect on temperate plants.

Moderate freeze – 28 F down to 24 F
Widely destructive effect on most leafy vegetation, with heavy damage to fruit blossoms. Many plants native to the Low Desert may freeze to the ground. Baby saguaros and other cactus seedlings killed unless sheltered under nurse plants.

Severe freeze – below 24 F
Many Middle Desert plants damaged. Some will die entirely. Much depends on the following day and how soon it warms up, and or gets sunny. Some Middle Desert native plants can stand these temperatures if it warms up early in the morning. Upper Elevation native plants are entirely genetically used to this.  Think pine trees in ski areas.

Frost Data Charts:

These are based include information based on the towns where the trackers of Google say you (yes, you dear readers) are located.  If I missed a place where you live, please let me know and I can get you that information.

Thanks for your visit today.
Jacqueline

More Details in my book

The Month By Month Guide offers tips for your landscape (yes even lawns and roses) in every month of the year.  I have a few copies left and am offering them to you – my loyal readers. When you buy from me you get a signed copy!

From the review:

“A great reference book is key to successful gardening in the region where you live. Arizona, Nevada & New Mexico Month-by-Month Gardening takes the guesswork out of gardening for anyone residing in the Southwest. With this book, you’ll know what to do each month to enjoy a thriving garden all year, from January to December. Chronologically organized, this guide is full of critical gardening when-to and how-to advice, along with illustrated step-by-step instructions.

The book’s author is Jacqueline Soule, a Tucson-based gardening expert. She knows this arid region inside and out, and she’s written several articles and books packed with her gardening advice. Arizona, Nevada & New Mexico Month-by-Month Gardening showcases Soule’s expertise in one easy-to-read guide.”

Profits from the sale of this book go to the Horticulture Therapy non-profit Tierra del Sol Institute.   Recent price increase, due to the US Postal Service price increase in July 2024.  It is now $30.

Or perhaps you wish Vegetable Garden Help

May I recommend my book?  The Southwest Fruit & Vegetable Guide offers not just growing guides but some of the latest varieties – including ones specifically for raised bed and container growing. Price is what you would pay on Amazon – only when you buy from me you get a signed copy!

From the review:

“In this updated 2nd edition of Southwest Fruit & Vegetable Gardening, you’ll find much-needed advice and practical tips on growing an edible garden, no matter which part of the southwestern US you call home.

Profits from the sale of this book go to the Arizona-based Horticulture Therapy non-profit Tierra del Sol Institute.

Legal Notes

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