Determining when to plant seeds in your Tray so that they are ready at the right time depends on a few factors: 1) the last frost date for your area, 2) what you want to plant and 3) how quickly each seed type germinates and grows into a seedling ready to transplant.
Last Frost Date
The last frost date is, on average, the last day in the spring that you might have a frost that can damage tender plants. It is a useful date to know when starting seeds indoors. A great resource for specific information for your area is a local master gardener, someone at a garden supply store or a local cooperative extension agent. You can also check the internet for Last Frost Dates in your part of the world.
Rate of Growth
You will find that seeds started in the Garden Starter Tray germinate and grow much faster than you may have experienced with other seed starting systems. That said, not all plants germinate and grow at the same rate. For example, tomatoes and peppers need about 6 weeks until the seedlings are ready for transplanting. In comparison, beans and cucumbers grow much quicker and need only 2 weeks of growth in the Garden Starter Tray until they are ready to transplant. This information is sometimes provided on the back of seed packets, but as with much gardening, the best guidance is from experience: your own, or a trusted expert at a gardening store or local cooperative extension service. Use this information with the last frost date to calculate the earliest date to start seeds.
When to Transplant
Some plants can withstand frost, others require frost free days and certain soil temperatures to thrive. For example, beets, lettuce and some flower seedlings can all be transplanted several weeks before the last frost. Summer crops, such as cucumbers, tomatoes, melons and beans, should only be transplanted after the last frost date. Your seed packet is the best source of “when to plant” information. Keep in mind, you do not need to seed the entire Tray at one time. Instead, you can stagger when you seed your Tray. For example, you can seed some Grow Sponges with spring crops that can withstand a frost, transplant the seedlings outside and then seed the remaining Grow Sponges with summer vegetables or flowers that need warmer outdoor weather to thrive.