The best time to start seeds in a cold weather greenhouse depends on the crops being grown, the local climate, and whether supplemental heating is available. Cold-hardy vegetables like spinach, kale, and lettuce can be started in late winter or early spring, as they tolerate cooler temperatures. If the greenhouse remains above freezing, seeds for hardy greens and root vegetables can be planted several weeks before the last expected frost.
Warmer-season crops like tomatoes and peppers require consistently higher temperatures and should be started once daytime temperatures reach at least 60°F. Using heat mats or insulated seed trays can help maintain proper germination conditions. Monitoring soil temperature and daylight hours ensures seedlings develop strong roots and healthy growth before transplanting outdoors or into larger containers.
