When to Start Your Seeds Indoors | Gardener's Supply (2024)

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Learn how to create a seedstarting schedule

By Kathy LaLiberte

Seedlings in a seed-starting tray. Photo: Carrie Bettencourt

Years ago, I was diligent about keeping a gardening journal. I didn't make daily entries like Thomas Jefferson and other famous journal keepers, but on a weekly basis I would record the major tasks I'd accomplished, a general weather summary (hot, dry, wet, cold), what plants were in bloom, and what crops were coming in. As my life became more and more crowded, those entries trailed off. It's a shame, because I really miss being able to peruse journal entries from years past. I would like to be able to remember when I picked my first tomato, or whether the lilacs bloomed early or late. But all those rich and wonderful details of prior gardening seasons are now lost.

One piece of record-keeping that I have managed to maintain are my annual seed starting calendars. I do know which week I planted my pepper seeds last winter, and the date I sowed the alyssum. And I know whether I started my onion seeds earlier or later than the year before. Because I start over 40 types of plants from seed (and about 70 different varieties), my seedstarting schedule is essential.

You'll find my own schedule below for reference, sorted by "start" week before last frost date. But this is not necessarily the exact schedule I'd recommend for you. I garden at the cold edge of zone 4. My grow lights are in a cool upstairs bedroom where seedlings grow quite slowly. But once it's April, all the seedlings go out into my warm and sunny greenhouse where they grow very rapidly. Each year, I consult my records and make a few adjustments to my schedule. My goal is to produce seedlings that are mature—but not overgrown—when it's time to go into the garden.

When to start (before your last frost date)	What to start
11 weeks	heliotrope, candytuft, primula, leek, viola, snapdragon, early greens (to be planted out in the cold frame or greenhouse beds)
10 weeks	delphinium, matricaria, onion, parsley, Greek oregano, impatiens, rudbeckia, early broccoli
9 weeks	pepper, coleus, shallot, eggplant, cherry tomato
8 weeks	tomato, alyssum, cleome, salvia horminum
7 weeks	ageratum, zinnia, more lettuce, radicchio
6 weeks	bachelor's buttons, agastache, aster, basil, marigold, sweet pea, calendula
5 weeks	sanvitalia, cabbage, convolvulus, nicotiana, lavatera, nigella, phlox, phacelia
4 weeks	morning glory, nasturtium, melon, cucumber, squash

Your own seed starting conditions are probably quite different from mine, and your planting schedule should be adjusted accordingly. Asking a garden-savvy neighbor when they sow their seeds is one easy way to get started. But if you want to figure out your own planting schedule from scratch, here's how to do it:

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Seed packets, sorted by planting date.

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, lavatera, nasturtiums, sunflowers, bachelor's buttons, nigella 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. Unfortunately, you'll probably find that planting instructions are pretty vague. Home gardeners would have a much easier time if seed companies would provide us with the information we need. At the very least, you should find something like, "For earliest bloom or fruit production, start 6 to 8 weeks before last frost date."

Sort your packets into piles according to these recommendations, 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. For detailed instructions on starting 500 varieties of annual and perennial flowers, I highly recommend Eileen Powell's book, From Seed to Bloom (Storey 1995).

Creating the Calendar

Start by finding the average last frost date in your area. You can get frost dates online by entering your zip code. To calculate your planting dates, you need to count back from last frost date in one-week increments. (I base my calendar on Saturdays, because that's the day that I usually have available for seedstarting). In my area, the last frost date is May 15. For me, when I count back from May 15, Week 4 is April 15, Week 11 is the week of February 26, etc. 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.

Making Adjustments

Now that you have a great schedule, here are a couple reasons you may want to make some adjustments:

Start earlier: Seeds take longer to germinate and plants grow more slowly when air and soil temperatures are cool (below 70 degrees F). If you plan to start your seeds in a cool basem*nt 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 other season-extending techniques, such as row covers or pop-up covers — 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.

A pop-up-style cover protects transplants from spring chills.

Start later: If you grow your seedlings in a greenhouse or an especially warm room (more than 70 degrees F.), 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.

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FAQs

When to Start Your Seeds Indoors | Gardener's Supply? ›

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.

What month is best to start seeds indoors? ›

Mid-March is the best time to start many vegetables and annual flowers indoors for transplanting outside once the threat of frost has passed.

When should I start seeds indoors in my area? ›

When should you start seeds indoors? Start seeds six to eight weeks before the last frost in your area. 2 Most plants are ready to go outside four to six weeks after you start the seeds.

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Can you start seeds indoors too early? ›

If you start too early, you might end up with leggy, overgrown plants that need babying until the frost disappears and the soil warms. Start too late, and you'll be drooling over your neighbor's BLTs while forlornly waiting for your plants' blooms to turn into fruit.

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What are the best conditions for starting seeds indoors? ›

Most seeds will not germinate without sunlight and will perform best with 12 to 16 hours each day. Indoors, place seed containers in a sunny, south-facing window and give the container a quarter turn each day to prevent the seedlings from overreaching toward the light and developing weak, elongated stems.

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Is February too early to start seeds indoors? ›

Most seeds require about a 6-8 week growing period before they're ready to be transplanted, which means the bulk of your indoor seeding should happen in February (early-to-mid February for Alexandria, and mid-to-late February for Lothian).

Learn More Now ›

Is April too late to start seeds? ›

April is the best time to plant most of your vegetable seeds after your last frost for all zones. It's still not too late to plant tomatoes and peppers from seeds as well! Check out the below vegetables that can be started in April. Be sure to check your gardening zone for last frost dates.

Tell Me More ›

Can I start seeds in January? ›

Look through your catalogs and find the vegetable seeds for your garden. Some flower varieties should be started in January. In a warmer environment you can plant certain vegetables, but must be ready for a frost. Indoor herbs are always great to grow in a sunny windowsill.

How long can seedlings stay in egg cartons? ›

But you also can't leave your seedlings in their egg cartons for too long, waiting for the weather to heat up. Seedlings should be moved to the garden once the roots reach the bottom of the tray, but before they start to grow into a circle.

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When to start tomatoes indoors? ›

Quick to germinate and grow, tomato seeds are best sown indoors about six weeks before your average last frost date. (To determine your last frost date, ask a gardening neighbor or contact your Master Gardener program.).

Is March too early to start seeds indoors? ›

March is the perfect time to get those tomato and pepper seeds started indoors so they can be ready for an early spring planting! Also now is a great time to start planting cool weather vegetables that can withstand those last frost days of March and April.

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Is it too late to start seeds indoors in May? ›

You may think it's too late to grow all your favorite vegetables from seeds, but warm May temperatures have made the soil perfect for sowing seeds. Warm soil will allow for fast germination and growing plants!

When to Start Your Seeds Indoors | Gardener's Supply (2024)

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