To calculate the last frost date for greenhouse planting, start by researching your local area's average last frost date, which is typically based on historical climate data. This can be found through local agricultural extensions or online databases. Once you have an estimate for the last frost, adjust it for your greenhouse environment.
Greenhouses often maintain warmer temperatures than the outside environment due to insulation and passive solar heating. To refine the estimate, monitor the greenhouse temperature over several weeks in early spring, checking for any frosty conditions. This can be done using a thermometer or automated temperature monitoring system. If your greenhouse stays consistently above freezing, you may be able to plant earlier than the outdoor last frost date, but it’s important to factor in extreme cold snaps and potential heating requirements.
