Not sure when it's time to plant? This Clever Tool Takes the Guesswork Out of Spring Planting

A simple soil thermometer can help you plan the perfect garden. Planting too early or late can lead to disaster, but this tool helps you pick the optimal time.

Gardener transplants seedlings
(Image credit: AlexRaths / Getty Images)

Spring is the season for getting all your planting in order. It takes some serious effort to plan out which seeds to start indoors vs. outdoors. Figure out which seeds need to be stratified and what temperature it needs to be before transplanting delicate seedlings. It’s a lot. Luckily, there is one simple measurement you can take that will help you know when to begin planting outdoors.

Determining soil temperature is critical to the success of your transplanted seedlings and seeds sown outdoors. If seeds are sown too early, the ground will be too cold for them to germinate and they can begin to rot with spring rainfall. Even seedlings you diligently started indoors can be ruined by planting too early or too late.

A soil thermometer is an inexpensive, crucial tool that tells you exactly when the ground is ready, guaranteeing a higher success rate for your spring garden. Read on to learn more about how a soil thermometer can up your gardening game.

Article continues below

Air Temperature vs. Soil Temperature

Checking the temperature of a hot composting pile

(Image credit: Alamy)

Day-time air temperature can be deceiving when determining when to plant seeds and when to transplant seedlings in the garden. A warm and sunny spring day makes you think it is time to get planting, but air temperature is only half of the story.

Soil holds on to cool temperatures longer and needs many days of warm weather to be suitable for some seeds to germinate. Soil temperature is important to the success of seed germination and to the health of newly transplanted seedlings. The perfect temperature for planting varies depending upon the variety of vegetable or fruit. Tomatoes, cucumbers, and peas need soil temperatures of at least 60 degrees Fahrenheit (15.5 C) and others like okra prefer up to 90 degrees Fahrenheit (32 C)! A simple soil thermometer can help you make the most of your gardening experience.

How to Use It Correctly

Now that you have your soil thermometer, what do you do with it? The best way to determine soil temperature is by taking readings in the early morning. This is when the ground will be at its coolest and will let you know if it is safe for your seedlings or will allow your seeds to germinate.

Insert your thermometer probe 2 to 3 inches (5-7.6 cm) into the soil for taking a reading for seeds. And sample at least 4 to 6 inches (10-15 cm) deep for transplants. Hold the probe in the soil for one minute and note the temperature. Take soil temp readings three consecutive days to get an average reading. This will be more accurate than just a single reading one day.

Shop Spring Planting Essentials

Kathleen Walters
Content Editor

Kathleen Walters joined Gardening Know How as a Content Editor in 2024, but she grew up helping her mom in the garden. She holds a bachelor’s degree in History from Miami University and a master’s degree in Public History from Wright State University. Before this, Kathleen worked for almost a decade as a Park Ranger with the National Park Service in Dayton, Ohio. The Huffman Prairie is one of her favorite places to explore native plants and get inspired. She has been working to turn her front yard into a pollinator garden.