We know spring is in the air when this question begins to be asked by Maryland residents who contact our horticulturists. While this date can fluctuate from year to year, historical temperature data provides a guide to help predict this very important date.
To find your average last frost date, enter your location or zip code into the frost date app from The National Gardening Association: https://garden.org/apps/frost-dates/.
You will receive a chart like the example below:
Frederick, MD | 10% | 30% | 50% | 70% | 90% |
Last 32° | Apr 19 | Apr 13 | Apr 9 | Apr 4 | Mar 29 |
The chart indicates a 10% chance that the temperature will go down to 32°F on April 19. There is a 90% chance of 32°F on March 29. In other words, April 19 has a lower probability of a freeze and would be a "safer" planting date. You would still have to monitor your local weather forecast. This data is derived from the 1981–2010 U.S. Climate Normals from NOAA.
Much planning and effort go into planting a vegetable and flower garden and so gardeners anticipate this date with great expectation. The last frost date in the spring and the first frost date in the fall dictate how long your growing season will be. If you want to grow plants from seeds indoors, you need this date in order to determine when to start your seeds. If you buy plants from a garden center or nursery, it is important to know this date so you can plan when to put your plants in the garden and minimize the risk of cold damage.