Starting Seeds Indoors: How and When to Start Seeds

Learn All About Starting Vegetable Seeds Indoors

March 19, 2020
Cabbage Seedlings
Pixabay

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 Indoors Start Outdoors Variable
Broccoli Beets Beans
Brussels Sprouts Carrots Celery
Cabbage Corn Kale
Cauliflower Garlic Spinach
Eggplant Okra  
Lettuce Onions  
Peppers Peas  
Pumpkins Parsnips  
Swiss Chard Potatoes  
Tomatoes Radishes  
Watermelons Squash/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.

    SUPER DISCOUNT!

    Celebrate Almanac Tradition and Save 57% with a Charter Membership in The Old Farmer’s Almanac Best Value Club

    Best Value Club

    You are invited to join The Old Farmer’s Almanac Best Value Club at a Special Savings!

    An incredible value—57% off for you!
    For traditional Almanac fans:
    Just $29.97! You save 57%!

    Get the best value for your Almanac dollar with these essentials. Claim you Old Farmer’s Almanac Best Value Club Charter Membership today!

    YES, sign me up now!

    Reader Comments

    Leave a Comment

    seedling growth

    Some of my seedlings have grown rapidly and are getting "leggy." Do I pinch off / back the top set of leaves after the 2nd set of leaves appear? Thanks.

    Leggy Seedlings

    The Editors's picture

    No, legginess is a sign of too little light, so you’ll want to move them to a brighter spot, if possible. A sunny window, or even a not-so-sunny window and some supplemental lighting should help. Pinching them back will likely stunt their growth or even kill them at this point, so refrain from doing that!

    Depending on what kind of plant they are, it may be time to replant them in larger pots. Leggy tomato seedlings, for example, can be planted about halfway up to their leaves, as new roots will sprout from the stem. This is not the case for most other seedlings, though.

    Seedlings

    Hi there, this is my first year planting seeds indoors and I am just wondering, do I leave the seedlings under the lights under I start the hardening off process OR once I transfer them to bigger containers can I then put them in my living room (most sun exposure) till they are ready to go outside...... I've researched online but there is soooo much information out there

    Seedling Lighting

    The Editors's picture

    Until they are planted outside permanently, the seedlings should be given as much light as possible indoors. After transplanting to larger containers, we would recommend keeping them under the lights for at least a few more days, as this will allow them to recover before being exposed to harsher light.

    After that, you can keep them in your living room with more sun exposure, but bear in mind that they will still be fragile and should be provided with enough water. Also be sure to rotate them every couple of days to ensure even growth!

    mold on seed pots

    I started my seeds indoor in cardboard cups and last years potting soil that was supposed to be suitable for seeds. After the first week I have little plants coming up but blueish green mold (?) around the boarders of the cups. Is that a concern?

    Mold on Seed Pots

    The Editors's picture

    Hi Deborah, The blue-green mold could become an issue if it moves to the roots of the seedlings. A cause of the mold could be that the soil is too wet, and that there isn’t enough airflow. An easy fix is to have a small, low-power fan running nearby to provide air circulation. 

    another reason for starting your own seeds

    Another good reason for starting your own seeds is succession planting. You can fill any empty spots as they come open in your garden by starting seeds at times when plants are no longer available for purchase, or those plants are beyond their best date for transplanting. Thanks!

    strawberries

    Hi there,
    when do I plant strawberry seeds -- to be used in hanging baskets
    thank you

    Planting strawberries in pots

    The Editors's picture

    Late spring is the right time of year to plant bare-root runners that have been cold-stored. Brought out of the cold and sold on, they will get away very quickly indeed to give a pick of fruits in as little as two months. Or, you can plant regular pot-sold strawberries which should also bear fruit in the same summer.

    7 day free trial

    I created a sign on and the only way I can use this app is on my desk top computer. I have a phone and a tablet, which is convenient to accompany me in my garden. This seems more of an inconvenience if I have to write it down to transfer onto my computer. Do you have any idea how long it will be before you have it available for phones/tablets?

    viewing your plan on mobile.

    The Editors's picture

    Hi Deborah, It sounds like you need to bring our garden plan out to the garden. This is possible on any mobile device. If you wish to view a plan that you made in the PC/Mac Garden Planner on any mobile device (including Android), you can simply use the ‘Publish Plan to Web’ feature of the Garden Planner (the button next to the Print button) to upload a copy to our web servers, so the plan and plant list can be viewed on any device.

    FYI, we are currently working on a new version of the Garden Planner that won’t rely on Flash Player, which it currently runs on and which is not supported on mobile devices. Our recently released Garden Journal (included with your subscription) is the first phase of this work, and it will run on smartphones and tablets as well as computers; however it was only recently that the vector graphics capabilities of all browsers reached the performance level we require to re-write the Garden Planner into HTML5 and it’s a big project, so it will take more time to complete the work on the Planner itself. We expect it to be ready for release by early 2020, with support for mobile devices following after launch.

    If you have further questions, let us know!
     

    advertisements

    I can't read the article I was interested in because everytime I clicked on what I thought was a link to the article it was an ad. One I remember had something to do with VA benefits. I respect the Farmer's Almanac and I know there's useful information hidden under the ads, but I will have to look elsewhere for it.

    ads

    I can't read the article about starting seeds indoors there's a ad that covers it and it moves with the screen

    Managing Ads

    There is a place at the bottom of the ad that you can click on to remove the ad. Easy peasy.

    Spindly seedlings

    Following germination seedlings grow rapidly but with a very fine stem with first leaves some 20 cm or so above ground level within a matter of days . What am I doing wrong ? Your advice will be appreciated

    Spindly Seedlings

    They may well need brighter/more light. Then again, some seedlings are just like that.

    You can also try brushing the tops of the seedlings lightly, it simulates wind. I'd wait till they were bigger first. (It incourages stockiness.)

    Spindly Plants

    Sounds like you started your seeds in a warm area without a bright light. You are better off starting over and begin the new seeds in fresh potting soil and in the same location as you did your first ones. As soon as they sprout move them to a cool area (Around 50 degrees) and place a grow light down to where it is within a couple of inches above the plants. A simple grow light can be made by replacing the regular florescent bulbs in a shop light with all frequency bulbs. When plants begin to touch the bulbs raise the light a couple of inches. Do this until they can be moved outside during the day. It is also important to check moisture. I find the best way to do this is to feel the soil. If it is cool everything is cool (OK). If it doesn't feel cool add water. Good luck.

    Your help with gardening.

    Thank you!

    Miracal-Gro

    I am starting an herb garden and purchased Miracle-Gro potting mix before discovering this website. Is it okay to use to start my seedlings or should I buy the recommended vermiculite and perlite. Having little experience at growing any advice would be much appreciated!

    Potting Mix

    The Editors's picture

    Yes, that potting mix should be just fine. It likely contains vermiculite and perlite already, so just keep an eye on it to make sure it stays moist. If the mix also contains chunks of bark and other materials, you may want to sift the large pieces out in order to give your seedlings an easier time getting started (otherwise, they’ll have to grow around these obstacles). Happy planting!

    starting seeds hardening off

    More question then comment but do commercial green houses harden off the plants we buy from green houses?

    Greenhouses

    The Editors's picture

    In most cases, it’s safest to assume that the seedlings you buy have been grown indoors and will still need to be hardened off before being planted in your garden. They may not need to be coddled quite as much as home-grown seedlings, but it depends on the conditions inside the greenhouse they were grown in and how similar they were to local outdoor conditions.

    My seeds germinated sooner than expected

    I thought i did everything right. Two weeks ago I started my seeds indoors. I checked my "last frost date" (April 15), time til plant outdoors (6-8 weeks), days til germination (14 days average) checked it all on the calendar, grew with lights. I guess maybe i did it too well. My seedlings are HUGE! They aren't leggy, but are outgrowing their starting trays, How should i plant them up? What size peat pots should I use and then how do keep them well lit? Also can anyone advise on fertilizer after they are potted up?

    Go Kelly Go!

    You sure did everything right! Maybe you started a little early, but that sounds like a success story to me. The size of the pot depends on two things: what is in it, and how long before they go into the garden. I would suggest that with the great results you're having to use the biggest pot you can, because once the roots start poking through the peat they need to go into the ground - and at the rates your little babies are growing April 15th is a long way off. As far as lighting, if you can keep them under the same lights that would be best. Otherwise put them in a south-facing window. When you transplant them use good soil (personally I like Fox Farm's "Happy Frog") and you shouldn't have to fertilize them for a month or so.

    Root Riot plugs

    I have had GREAT success using Root Riot plugs for my seedlings. They keep moist but not wet - just the perfect moisture content for the seedlings. I also have the tray on a heat mat in a west-facing window so they get morning sun, but not all-day sun. Plus their initial waterings are made with a solution of diluted Mychorrizae (sp?). Even with seeds that are a couple years old, I still get strong germination rates.

    Sprouting Tip For Hard Shelled Seeds.

    Have you ever had peppers or tomato seedling leaves get stuck in their hard seed coat after germinating? I have, and it is not easy to remedy once it happens. My solution to this which I have been using for years is to plant the seed with the root tip UP, not down. When the seed root emerges, it makes an immediate U-turn downwards. What emerges above the soil is the middle of the seed stem in an inverted U shape. The leaves are still in the seed coat below the surface where it is still moist. Eventually the inverted U pulls the leaves up and out of the soil with the seed coat still buried. Works every time. Not so helpful on seeds that are difficult to tell which end is the root end (round seeds).

    Planting seeds under plastic.

    If I plant seeds under plastic do I take it off when seedlings appear? Also, do I have lights on only in the daytime?

    When they reach about 1 inch

    When they reach about 1 inch no more then 2 inch, take off the dome, the longer you keep the dome on, the taller and weaker the seedlings will grow, the longer they are the more apt they are to brake in the wind and such.

    seedlings

    Hello I have planted my seedling they were planted Friday April 22. Of course they have not sprouted yet but I have accidentally over watered them and was wondering what I could do or if I could put them in the sun to absorb the water. Please help

    watering seedlings

    The Editors's picture

    Does your seedling tray/pot have drainage holes? Make sure they are not clogged. (Stick a toothpick up the hole and wiggle around.) Are you using loose, well-draining soil? If not, you really have to repot. Don’t move the tray/pot to the sun until the roots are healthy again. Don’t water again until the surface of the soil is dry to the touch. However, do not try it out either or that’s just too much shock. Do not fertilize until the plant has recovered. We hope these tips help.

     

    Pages