How to Calculate Last Frost Dates

Each year, there are two periods of frost: the first frost, which occurs in the autumn, and the last frost, which occurs in the spring. The last frost is so-named, because it marks the end of the winter, and the beginning of the new planting season. It's essential to know the last frost date before planting new seeds, because it's difficult -- or even impossible -- for many seeds to germinate during a frost period. Keep in mind however, that last frost dates are only predictions. The weather can change each year.

Instructions

- 1
  Log onto Almanac.com. This is the website of the Old Farmers Almanac. This publication has been providing long-range weather predictions and tide-tables since 1792.
- 2
  Click the "Gardening" link on the left-hand side of the page to open a sub-menu.
- 3
  Click the link that says "Frost Dates" located beneath the Gardening section.
- 4
  Scroll down the list to find an area near you. If you see a city near you, take note of the last frost date indicated by the chart. If you don't see a city, scroll down until you see a link that says "For more locations click here."
- 5
  Click your state, as found in the "Select a State" box. This will open a PDF document with a detailed list of your state's cities listed in alphabetical order.
- 6
  Find your city in the left-most column and match it with the three boxes found under the "Spring (Date)" column. The subcategory "90" means that there's a 90 percent chance of a freeze on that date. The subcategory "50" means that there's a 50 percent chance of a freeze on that date. The subcategory "10" means that there's a 10 percent chance of a freeze on that date. The later dates have higher probabilities of being the last frost date. However, there are no guarantees with weather.

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