When Can You Put Tomato Plants in an Unheated Greenhouse?

Greenhouses are an excellent way to extend the growing season for tomato plants. In colder climates, an unheated greenhouse allows you to start your tomato plants earlier in the year than you would be able to outdoors. But when is the right time to transplant your tomato plants into an unheated greenhouse? Here are some things to consider:

First Frost Date

Knowing your area's first frost date is crucial when deciding when to move your tomato plants to an unheated greenhouse. The first frost date is the date when you can expect the temperature to drop below 32°F. Tomatoes are sensitive to cold weather, and even a light frost can kill them. To be safe, you should transplant your tomato plants into the greenhouse two weeks after the first frost date has passed. This will give your plants time to recover from any recent cold snap and adjust to the new environment inside the greenhouse.

Soil Temperature

Tomato plants thrive in warm soil, so it's important that the soil inside your greenhouse is warm enough before transplanting. The ideal soil temperature for tomatoes is between 65°F and 85°F. If the temperature inside your unheated greenhouse is consistently below 65°F, it's not yet time to transplant your tomato plants. You can use a soil thermometer to measure the temperature of the soil in your greenhouse. If the soil is too cold, you can warm it up by laying down a layer of black plastic or using a space heater for a few days before transplanting.

Daytime Temperatures

Tomatoes are sun-loving plants and need plenty of light and warmth to grow and mature. It's essential to monitor the daytime temperatures inside your unheated greenhouse before transplanting your tomato plants. If the daytime temperature is consistently below 60°F, it's still too cold for your tomato plants. You should wait until the daytime temperature is consistently above 60°F before transplanting your tomato plants.

Acclimation Period

Once you are confident that the soil and daytime temperatures inside your unheated greenhouse are suitable for your tomato plants, it's time to begin the acclimation process. This process involves exposing your plants to the greenhouse environment gradually. You can start by leaving your plants in the greenhouse for a few hours each day and gradually increasing the time over a week or so. This will allow your plants to adjust to the new environment and harden off before being exposed to the greenhouse's full conditions.

In Conclusion

Transplanting your tomato plants to an unheated greenhouse can extend your growing season, but it's essential to do it at the right time. Factors like the first frost date, soil temperature, and daytime temperatures inside your greenhouse should all be considered. Once you are confident that your plants will have the necessary conditions to thrive, be sure to give them an acclimation period so they can adjust gradually to their new environment. With the right timing and proper care, your tomato plants will produce a bountiful harvest inside your unheated greenhouse.