You can start seeds indoors before you are ready to do your outdoor planting. It is most common to do this in the spring, before the last frost. But, you can also start your seeds indoors during the hot summer months in preparation for a fall planting of some cool season vegetables. After you have started your seeds indoors and they appear to be thriving, when is it time to transplant?
About 3 weeks after sprouting, your seedlings should have 2-3 sets of true leaves. At this point the cotyledons have died off and you should have only one seedling per pot or cell (thin any extras). Depending on the size of your container, you may need to repot to a larger container to allow the roots plenty of room to grow before transplanting outside. You don’t want to crowd your little plants. Make sure the container is big enough so the plant learns before going outside that their roots are allowed to stretch, grow, and thrive.
About 10 -14 days before your expected transplant date (when the danger of frost will have passed), begin to harden off your plants. Do this by taking them outside to a wind sheltered spot for an hour the first day then bring them back inside. On the second day try for two hours outside, then bring them back inside. Continue to increase the time spent outside each day until the plants have spent the whole day outside. This will prevent shock when they get put in the ground.
Your seedlings are ready to transplant when they look strong and vibrant. Make sure your garden soil is well prepared and you have amended your soil if needed. Make the hole in your garden space and carefully remove your plant with its soil from the transplant container. Gently break up any roots balls that may have formed and put your plant in the hole. Water thoroughly.