Many gardeners start seeds too early, causing problems in growth and development of a plant that would otherwise be healthy and beautiful! Growing indoors is fun and easy, once you know how to properly provide and care for your plants. Here is some great information on when to start seeds indoors for optimum growth and performance.
Sort your Seed Packets
Start by separating all your packets of seed into two piles: those that will be "direct-sown" (planted right in the garden) and those that will be started indoors. The outdoors pile will include most vegetables, such as peas, beans, corn, radishes, carrots, beets, lettuce, spinach, melons, cucumbers, and squash. Put a rubber band around whatever seeds you'll be planting outdoors and set them aside.
Most annual flowers will also go into the direct-sow pile: zinnias, asters, nasturtiums, sunflowers, bachelor's buttons, and calendula. If your growing season is very short or your garden conditions are especially difficult, you may decide to put some of these annual flowers into your "sow indoors" pile. Most perennial flowers will need to be started indoors.
Now spread out your "sow indoors" pile and start reading the back of the seed packets. Sort your packets into piles according to these directions, making separate piles for 5, 7, 9 weeks, and so on. Some packets, especially those for perennials, may only tell you how long it takes the seeds to germinate. If that's all you have to go on, take that figure (which is usually a range) and add 6 weeks. Then put the packet into the appropriate pile.
If there's no information on the seed packet, you can pretty safely just start all your seeds about 6 weeks before you'll plant them outdoors. Make note of which plants are too big or too small at planting time, and then you can make adjustments next year based on your notes.
Creating the Calendar
To calculate your planting dates, you need to count back from the last frost date in one-week increments. Some gardeners base their calendar on Saturdays, because that is the day most gardeners have time to plant. Ask a local gardener or call your local extension service if you don't know the last frost date for your area. Simply write the week number (8,4, 6 or whatever) on each seed packet and use a rubber band to keep each pile together. When the planting week arrives, you just grab the right packet and start planting.
Now that you have a great schedule, here are a couple reasons you may want to make some adjustments:
Start earlier: When air and soil temperatures are cool (below 70 degrees F), seeds take longer to germinate and plants grow more slowly. If you plan to start your seeds in a cool basement or cool bedroom, you may want to shift your whole schedule a week or two earlier.
You can see on my schedule that I start some greens and broccoli at the end of February. That's because these seedlings get planted outside about a month before the last frost date. If you have a cold frame or greenhouse, or if you use row covers or water-filled teepees, you can plant tender seedlings several weeks before the last frost date. Just count back from that expected planting date to get the right date to sow your seeds.
Start later: If you grow your seedlings in a greenhouse or a very warm room, you should cut a week or more out of your schedule. Heat promotes rapid growth, and you could find yourself with giant plants that are ready for the garden before warm weather arrives.