Starting Seeds Indoors: How and When to Start Seeds

Starting seeds properly can make or break your entire growing season! Here’s what you should know about starting seeds, including when to do it, which seeds to start indoors (or outdoors), and how to do it correctly.

Why Start from Seeds?

Rather than start vegetables from seed, many folks opt to just buy young plants from commercial sources. While there’s certainly nothing wrong with that practice (in fact, it can save you from a few headaches later on), there are good reasons to start your own plants, too!

  • Mainly, people start seeds in order to get a jump on the gardening season.
    • In regions with short growing seasons, starting seeds indoors allows you to gain a few precious weeks of growing time, which can really make a difference when frost looms in the fall. 
    • In warmer regions, starting seeds indoors can allow you to get in an extra round of crops (especially cool-weather crops) before the heat of summer stifles growth. 
  • If you want to grow a lot of plants, buying packs of seeds is usually cheaper than buying individual seedlings from the nursery.
  • While some nursery plants are grown really nicely, others are poor quality. When you plant your own seeds, you have control over the way the young plant is raised. This may be especially important if you are an organic gardener.
  • Finally, there isn’t always a great selection of plants at local nurseries. When you plant from seed, you have a much wider choice of varieties, tastes, and textures—and you can experiment with new ones, too!

Which Seeds Should You Start Indoors?

Consult the table below to see which crops are typically started indoors, which are typically started outdoors, and which can be variable. (Note that gardeners in warmer climates will be able to start more crops outdoors than gardeners in colder climates.) 

Keep in mind that there isn’t a hard-and-fast rule about what you can start indoors and outdoors; it varies by your experience, your location, and the plant itself.

It is important to consider how each type of vegetable grows. For example, root vegetables like carrots and beets don’t like having their roots disturbed, so it’s usually safer to just start them outdoors in the ground rather than transplant them later on. Meanwhile, veggies like tomatoes and peppers are very susceptible to the cold temperatures of spring, so it’s best to start them indoors and keep them safe from unpredictable weather. Finally, plants like peas are so fast growing and cold tolerant that it just makes sense to get them right in the ground! 

For seed-starting information customized to your location, check out our free online Planting Calendar.

Start IndoorsStart OutdoorsVariable
BroccoliBeetsBeans
Brussels SproutsCarrotsCelery
CabbageCornKale
CauliflowerGarlicSpinach
EggplantOkra 
LettuceOnions 
PeppersPeas 
PumpkinsParsnips 
Swiss ChardPotatoes 
TomatoesRadishes 
WatermelonsSquash/Zucchini 
 Sweet Potatoes 

Before You Start Seeds

  • Be seed-savvy. Obtain seed catalogs from several companies and compare their offering and prices. Some of the regional companies may carry varieties better suited to your area.
  • Make a list of what you’d like to grow. A good rule-of-thumb is to imagine your garden one-quarter the size that it really is. This allows for good spacing practices! See Vegetable Gardening for Beginners for popular beginner vegetables.
  • Prepare for some losses. Though it’s good not to plant too much for your garden space, it’s also good to assume that some of your seeds won’t germinate, or that they will inexplicably die off later. Plant a few extra, just in case.
  • Consider a grow light if you start in late winter. Most veggies need between 6 to 8 hours of direct sun (minimum), so it’s important to have a grow light if you are sowing your vegetable seeds indoors in late winter. A grow light will also keep your seedlings from getting too leggy. Learn more about using grow lights.
  • Team up with a neighbor and share seeds if you have leftovers!
  • Use clean containers. Most seed catalogs offer seedling flats, peat pots, and other growing containers, but egg cartons make good containers for the earliest stages of seed starting, too. Be sure to poke holes in the sides near the bottom of the containers you use in order to allow excess water to drain. Keep in mind that you might need to transplant your seedlings into larger containers at some point before moving them into the garden.
  • Label your containers now! There’s nothing more frustrating than forgetting what you planted, especially when you are testing out different varieties of the same plant.
Seedlings. Photo by Sergii Kononenko/Shutterstock
Photo by Sergii Kononenko/Shutterstock

When to Start Seeds Indoors

  • We’ll get right to the answer: Just check our Planting Calendar, which lists the ideal dates to start your vegetables indoors. We’ve created a customized tool that’s based on your zip code and local frost dates!
  • As a general rule, most annual vegetables should be sown indoors about six weeks before the last frost in your area. See local frost dates.
  • Don’t start your seeds too early, especially tomatoes. Wait until six weeks before your last frost date to start tomato seeds.

How to Start Seeds

  1. Fill clean containers with a moistened potting mix made for seedlings. If you don’t use a pre-made seed-starting mix, you can make your own by combining peat and equal parts vermiculite and perlite (see the video on creating your own seed-starting mix further down on this page). This combination holds enough water, but allows oxygen to flow and the delicate roots to easily penetrate the soil. Don’t use regular potting soil, as it may not be fine enough for seeds to root through properly. Pre-formed seed starters (such as Jiffy pellets) work well, too.
  2. Plant your seeds at the depth listed on the seed packet. Most seeds can simply be gently pressed into the mixture; you can use the eraser end of a pencil to do so. When choosing which seeds to plant, choose the largest seeds in the packet for the best chance at germination.
  3. Cover containers loosely with plastic or an otherwise clear, waterproof covering to keep them from drying out too quickly. Poke a few holes in the plastic with a toothpick for ventilation; mold growth can occur if containers are not allowed to “breath.”
  4. Water newly started seeds carefully. A pitcher may let the water out too forcefully, dislodging the seeds or young seedlings’ fragile roots. A mist sprayer is gentle but can take a long time. We recommend using a meat-basting syringe (aka “turkey baster”), which will dispense the water effectively without causing too much soil disruption.
  5. When seedlings start to appear, remove the plastic covering and move containers to a bright window or under grow lights. 
  6. When the seedlings get their second pair of leaves, prepare individual pots filled with a potting mix with plenty of compost. Move the seedlings carefully to the new pots and water well. Keep seedlings out of direct sun for a few days, until they’ve had a chance to establish themselves in their new pots.
  7. As seedlings continue to grow, be sure to water them as needed; while young, they are very susceptible to drying out.

Tips for Success:

  • You may have to soak, scratch, or chill seeds before planting, as directed on packet.
  • Seeds sprout best at temperatures of 65-75°F (18-24°C).
  • Find a place in the kitchen where there is natural bottom heat—on top of the refrigerator or near the oven are good spots. (Move the tray if the oven is on, as it may become too hot!)
  • If you keep your seedlings next to a window, remember to rotate the containers every so often to keep the seedlings growing evenly. If you’re using a grow light, remember to raise it a few inches above the tallest seedling every couple of days.

Make Your Own Seed-Starting Mix

Seeds should be planted in a potting mix that caters specifically to their delicate roots and sensitivity to moisture. It’s easy enough to buy a pre-made seed-starting mix—or, create your own:

Moving Seedlings Outside (aka “Hardening Off”)

Before transplanting seedlings to your garden, you’ll first need to do something called “hardening off.” This will prepare the seedlings for the harsh realities (i.e., climate) of the outside world! 

  1. During their last week indoors, withhold fertilizer and water them less often.
  2. Seven to ten days before transplanting, set the seedlings outdoors in dappled shade that is protected from winds for a few hours each day, gradually increasing their exposure to full sun and windy conditions. This is the hardening-off period.
  3. Keep the soil moist at all times during this period. Dry air and spring breezes can result in rapid transpiration. If possible, transplant on overcast days or in the early morning, when the sun won’t be too harsh.

Watch our video on hardening off for more info:

How to Transplant Seedlings

After the hardening-off period, your seedlings are ready for transplanting. Here are a few tips:

  • Set transplants into loose, well-aerated soil. Such soil should capture and retain moisture, drain well, and allow easy penetration by the seedlings’ roots.
  • Soak the soil around new seedlings immediately after transplanting.
  • Spread a light layer of mulch to reduce soil moisture loss and to control weeds.
  • To ensure the availability of phosphorus in the root zone of new transplants (phosphorus promotes strong root development), mix 2 tablespoons of a 15-30-15 starter fertilizer into a gallon of water (1 tablespoon for vining crops such as melons and cucumbers), and give each seedling a cup of the solution after transplanting. 

Read more about transplanting seedlings.

Tomato seedlings

Learn More About Gardening

Here’s another “quick and easy” method to plant seeds. Also check out our video on the top tips for starting seeds.

Also, consult our library of Growing Guides, which provide planting, care, and harvesting information for all the common vegetables, fruit, and herbs.

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