Starting Seeds Indoors: How and When to Start Seeds

All About How to Start Vegetable Seeds Inside

January 6, 2021
Cabbage Seedlings
Pixabay

Learn how to start seeds indoors, when to start seeds indoors, and which vegetable seeds should be started indoors from The Old Farmer’s Almanac.

Why Start from Seeds?

When planning for a garden, a key thing to consider is whether you want to start your garden from seeds or from young plants (“transplants”) bought from a local nursery.

Each option has its advantages and disadvantages. Buying transplants is certainly a lot easier and more convenient, but you are also limited to only growing the types of vegetables and flowers that you can find. Seeds, on the other hand, offer a wide range of varieties to try. Here are the main things to think about:

  • 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 may be of 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!

For absolute beginners, it’s not a bad idea to start off with buying transplants, as you won’t have to stress over things like the timing of starting seeds or the care of young seedlings. That being said, there are many vegetables—such as carrots and radishes—that do best when started from seed, so consider employing both methods to suit your needs.

Pepper seedlings

Starting Seeds Indoors vs. Outdoors

Once you’ve decided to try your hand at starting your own seeds, it’s time to think about starting them indoors or outdoors. There are many benefits to starting seeds indoors rather than waiting to sow them outdoors (aka “direct-sowing”). The main reason is to get an early start on the gardening season, but that’s not the only consideration:

  • In colder climates 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. Slow-growing crops such as tomatoes may not even have enough time to reach maturity if they are started outdoors.
  • 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. 

See our article about direct-sowing seeds outdoors for more information on that topic.

Which Seeds Should You Start Indoors?

Not all seeds should be started indoors. In fact, most vegetables grow perfectly well when started outdoors and even prefer not to be transplanted. Ultimately, it’s important to consider how each type of vegetable grows.

Consult the table below to see which crops are typically started indoors and which are typically started outdoors. 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 personal preference, your location, and the plant itself.

  • Crops that are best started indoors include broccoli, brussels sprouts, cabbage, lettuce, and tomatoes. Those with a slower root development, like cauliflower, celery, eggplant, and peppers, should also be started indoors.
  • Tender vegetables like tomatoes, eggplants, 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.
  • Plants that do not transplant well and are therefore best started outdoors or in containers include cucumbers, muskmelon, pumpkins, squash, and watermelon. These are all tender, however, so refrain from sowing them outdoors while frost is still a threat.
  • Some plants truly resist transplanting. For example, root vegetables like carrots and beets don’t like having their roots disturbed, so it’s usually safer to just start their seeds outdoors in the ground rather than transplant them later on. Plants with long tap roots also do not like to be transplanted; examples include dill and parsley.
  • Finally, plants like radishes and 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.

Seed-Starting Preference by Plant

Plant Start Indoors Start Outdoors (Direct-Sow)
Arugula   X
Beets   X
Broccoli X  
Brussels Sprouts X  
Cabbage X  
Carrots   X
Cauliflower X  
Celery X  
Corn   X
Cucumbers   X
Eggplant X  
Green Beans   X
Kale   X
Kohlrabi   X
Lettuce X X
Okra   X
Onions   X
Parsnips   X
Peas   X
Peppers X  
Potatoes   X
Pumpkins   X
Radishes   X
Rutabagas   X
Spinach   X
Squash (Summer)   X
Squash (Winter)   X
Sweet Potatoes   X
Swiss Chard   X
Tomatoes X  
Turnips   X
Watermelons   X

Tips Before You Start Seeds Indoors

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. You may have to soak, scratch, or chill seeds before planting, as directed on packet.
  8. Seeds sprout best at temperatures of 65 to 75°F (18-24°C). Don’t let it get too cold.
  9. Rotate your seedlngs. 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.

Seedlings. Photo by Sergii Kononenko/Shutterstock
Photo by Sergii Kononenko/Shutterstock

When to Start Seeds Indoors

  • Our Planting Calendar 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.
  • Do not sow too early in the season or you’ll end up having to transplant seedlings into bigger containers more often because conditions outside still aren’t suitable for outdoor planting. 
  • Your packet of seeds will often list when the seeds should be started indoors. For example, it may say, “start indoors 8 weeks before last expected frost date in your area.”

Types of Seed-Starting Containers

Plastic Food Containers (Yogurt Cups, Sour Cream Containers, etc.)

Plastic food containers such as yogurt cups or sour cream containers make for excellent seed-starting pots. Simply clean them out and poke a few drainage holes in their bottoms. They are generally large enough to house one or two small seedlings for a few weeks. Eventually, seedlings will need to be transplanted into their own pots.

Seed Flats or Trays

A seed flat or tray is a single tray-like container that is useful for sowing very tiny seeds such as basil or easy-to-transplant flower seeds. The seeds are sown in the tray and, when big enough to handle, are transplanted on to their own individual pots or plug trays. The compact size of seed trays makes for a very efficient use of space during this first stage of growth.

  • For easy cool-season crops—everything from onions to celery to cabbage—you can sow multiple seeds in the same container or seed flat. You can even stack trays up after sowing to save on space. After two or three days, start checking daily for signs of germination then move them out to the greenhouse or cold frame to continue growing. Or you can continue to grow seedlings on indoors, using grow lights to ensure strong, even growth.
  • Note: Larger seedlings, or those of tender crops such as tomatoes or peppers, will likely need to be potted up to a larger container at least once. They grow fast and will need to be pricked out into individual pots before they are transplanted into their final outdoor growing spots once the threat of frost has passed.

Plug Trays

Plug trays are basically containers with individual pockets for each seed. They minimize root disturbance and save time, because often seedlings can go straight from their plug tray to the outdoors.

  • Trays with smaller plugs suit most leafy greens and radishes, especially if they will be transplanted promptly (within three or four weeks of sowing).
  • Those with larger plugs are great for sowing chunkier seeds such as beans and bigger, hungrier seedlings such as those of the brassica family (broccoli, cabbage, cauliflower, etc.). 

Well-made trays of rigid plastic can potentially last for many years, but if you want to avoid plastic, look for alternatives made of biodegradable fiber. 

How to Sow Seeds

  1. Fill clean containers with an all-purpose potting mix or seed compost. Pre-formed seed starters (such as Jiffy pellets) work well, too. Do NOT use regular potting soil. It’s not fine enough for many seeds’ roots to easily penetrate the soil and does not allow oxygen to flow. If you don’t use a pre-made seed-starting mix, see how to make your own seed-starting mix.
  2. If you are using plug trays, push potting mix down into the plugs with your fingers so it’s nice and firm, then add a little more potting mix.
  3. Now make shallow depressions with your fingertips. Plant your seeds into the depressions 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. Many vegetables, including common crops such as salads, onions, beets, peas, and radishes, may be sown in pinches of three to five seeds per plug for planting out as a cluster of seedlings. Larger seeds, like beans, are sown individually into deeper holes made with a finger, pencil, or dibber.
  4. Once you’re done sowing, sieve a little more potting mix over the top. Gently skim over the surface of the tray with your hands to ensure all the seeds are buried. Water trays carefully using a watering can or clean turkey baster. 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. Go over the trays a couple of times so that the potting mix is completely moistened through. Label trays with the variety and date of sowing.
  5. 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.”
  6. Check trays and pots regularly for moisture. Lifting them up is a good way to judge how much moisture there is in the potting mix. If it’s light, water. One way to achieve a thorough watering is to pop trays into a reservoir to soak up water through their drainage holes. Remove them once you can see it’s moist at the surface.
  7. When seedlings start to appear, remove the plastic covering and move containers to a bright window or under grow lights. 

VIDEO: Demonstrating How to Seed

See the seed-starting steps described above.

Pricking Out, Potting Up

If you grew seedlings all together in a tray, you can transfer them into their own plugs or pots of potting mix. Start pricking them out as soon as the seedlings are big enough to handle.

Carefully ease the seedlings out of the tray they were growing in then gently tease them apart. Try to retain as much of the original potting mix around the roots as you can. Work with small batches of seedlings so they don’t dry out while their roots are bare.

Make holes in the potting mix with your finger, a pencil, or something similar. Lift each seedling carefully and avoid pinching their delicate leaves, roots, and stems. Carefully feed the roots right down into the hole then gently firm the seedling in. You can bury some of the stem if the seedlings are looking a little leggy and drawn. This will help to support them.

Once you’re done, gently water the seedlings with a watering can. Don’t worry too much if the seedlings get a little flattened, they’ll soon recover.

Preparing Seedlings for Planting

Water seedlings to keep the potting mix moist, but be careful not to overwater. If you’re growing in a greenhouse, tunnel or cold frame, ventilate it on mild, sunny days. This will help keep the air inside moving, and reduce the risk of disease and molds.

Cool-season crops such as lettuce, onions, beets, or peas can go straight outside as soon as the ground is ready, meaning that the soil is no longer cold and wet, and has reached around 50ºF (10ºC). You can help encourage stronger seedlings in preparation for the move by occasionally running your hand gently over the seedlings.

Plant seedlings out while they are still quite young if outdoor conditions allow—sometimes as soon as three to four weeks after sowing. Younger seedlings tend to establish quicker than those that have become root bound in their containers.

VIDEO: Demonstrating Potting Up

Moving Seedlings Outside (aka “Hardening Off”)

    Once you have raised your seedlings indoors, it is important to take steps to acclimatize them to their new outdoor home however, or you risk losing your plants and wasting all that hard work. This is a process known to gardeners as “hardening off.” This will prepare the seedlings for the harsh realities (i.e., climate) of the outside world! 

    Hardening off should take a minimum of a week and may take up to two. Suddenly moving plants from a stable environment to one with wide variations in temperature, light and wind can seriously weaken plants.

    1. For most plants, start hardening off about a week before the final frost date for your area. See our Gardening Calendar for safe dates to plant outside and work back from there. Withhold fertilizer and water them less often.
    2. Seven to ten days before transplanting, set the seedlings outdoors in dappled shade for a short time. Make sure the spot is sheltered from winds.
    3. Gradually extend the amount of time that plants are outside over the course of a week or two, until they’re staying out all day.
    4. 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.

    If you’re not able to be around to bring your seedlings back in during the day, another option is to place your seedlings into a cold frame and gradually increase the amount of ventilation by opening vents progressively wider each day. Make sure to shut them down completely before dark.

    VIDEO: Demonstrating Hardening Off

    How to Transplant Seedlings

    After the hardening-off period, your seedlings are ready for transplanting. Read our article about transplanting seedlings.Consult our library of Growing Guides, which provide planting, care, and harvesting information for all the common vegetables, fruit, and herbs.

    Free Online Gardening Guides

    We’ve gathered all of our best beginner gardening guides into a step-by-step series designed to help you learn how to garden! Visit our complete Gardening for Everyone hub, where you’ll find a series of guides—all free! From selecting the right gardening spot to choosing the best vegetables to grow, our Almanac gardening experts are excited to teach gardening to everyone—whether it’s your 1st or 40th garden.

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    Reader Comments

    Leave a Comment

    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.

     

    question about seed timing in chicago.

    I was wondering if its still early enough to plant seeds for tomato plants in the chicago area? I started some seeds prior to this month but some had become leggy and dampening had affected some of them. so I was wondering if im able to still plant seeds and have decent size plants by the start of june or end of may?

    thanks

    mildew

    I have old seeds and wanted to see if they are viable, so I started them indoors early. Some of them have germinated, but I am noticing blotches of mildew on the soil. Did I hear peroxide and water will take care of this? If so, what is the ratio? Thank you for your help.

    mildew on soil

    The Editors's picture

    The most common cause of mildew on soil is high humidity. Increase the air circulation by lifting the lid (or whatever is covering your seedlings). See if you can scrape off the mildew without harming the seedlings.

    We would not recommend hydrogen peroxide on the plant at this time. It’s more of a container cleaning agent before you even start.

    When starting seeds, you want to be sure that your starting medium is viable, new/fresh, and soilless, which being very light discourages humidity and encourages circulation.

    We hope this helps.

    Seed starts in Western Ontario

    Hello! When should I start my veggie seeds here in this part of Ontario, Canada? If I started now, I'd expect it to be about 7-8 weeks before the last frost.

    Most vegetable and annual

    The Editors's picture

    Most vegetable and annual flower seeds can be started indoors about 6 weeks before the last frost. Check our Planting Dates for Seeds chart. Link is at the top of this page.

     

    seedlings

    What do I do if my seedlings are flowering but they cannot be moved outdoors for 3-4 weeks.

    Starting cucumber seeds

    At what point can I start germanating my cucumber seeds for my first garden. I live in south east Texas so I have no idea about last frost, so I want to be ahead of game but don't want to start to soon thanks

    cucumber seed starting

    The Editors's picture

    You might be interested in our cucumbers page here:

    http://www.almanac.com/plant/cucumbers

    On it, it says:

    • Cucumbers are seeded or transplanted outside in the ground no earlier than 2 weeks after last frost date. Cucumbers are extremely susceptible to frost damage; the soil must be at least 65ºF for germination. Do not plant outside too soon!
    • For an early crop, start cucumber seeds indoors about 3 weeks before you transplant them in the ground. They like bottom heat of about 70ºF (21ºC). If you don’t have a heat mat, put the seeds flat on top of the refrigerator or perch a few on top of the water heater.

    To find out your frost date, go to this page and type in your zip code:

    www.almanac.com/gardening/frostdates/

    Then, count back 3 weeks from the last expected spring frost date to find the date to sow the seeds indoors. Good luck!

     

    Perennial Seed starting

    Do you have an Indoor seed starting chart for annual/perennial flowers ?

    School Garden - starting some plants indoors -

    Hello! I am a teacher-librarian in a K-8 school in Bowmanville, Ontario. Our school is starting a habitat area on the school yard with some native plants (eg woodland sunflower, and hopefully a raised bed for veggies. I want to transform part of my large library space into an indoor growing space so we can start seedlings in the spring. What will I need in the space to start seeds indoors. It is in a corner with about 10 feet of two storey windows that face west and one window about 3 feet wide that faces north. Do I need special lighting?
    Also, is it possible for me to grow anything indoors through the winter? Herbs, maybe?
    I don't have a lot of background in gardening but lots of enthusiasm and a school full of students who want to learn to be responsible, sustainable citizens in suburbia.
    Thanks for your help. I have appreciated reading the comments you left for other folks.
    Brenda

    How early is too early

    Hi,

    I am in Ottawa, Ont. Canada.. Zone 5a.

    I am curious of early is too early to start plants indoors. I started some pepper plants and tomato plants beginning of Dec with hopes to grow mature plants and transfer them outdoors in april/may.

    I would still keep them in pots while hardening them off for 2 weeks before transplant.

    I will also start new seedlings in Feb to be safe but wanted to know if my December plants would help me get a bigger headstart or bigger headache than worth.

    and yes.. i have bigger pots and room in the house.

    starting seeds early

    The Editors's picture

    If you start seeds too early, it can make it difficult for the plant to survive transplant shock when transferred outdoors, even after they were hardened off. Also, keep track of the days to maturity. For example, if you have a determinate tomato plant that matures in 80 days, and it was growing indoors since mid-December, then it might produce fruit (if pollinated) before it gets transplanted out in April/May. It would probably be too hard on the plant once it is in fruit, but you can certainly try it: at that point, it might be best to just keep growing it indoors (especially if you have a greenhouse). Indeterminate tomato varieties might be better than determinate, as they might continue to flower and set fruit after recovering from transplant shock.

    Tomato seeds from last summer

    Tomato seeds from last summer reseeded in my vegetable garden and 4-5 of them look very healthy. Do you think they'll produce fruit, or since they were in the ground with very cold temps (in MD) over winter, should I throw them out?
    Thanks for your feedback.

    Hi Dana, Don't throw them

    The Editors's picture

    Hi Dana,
    Don't throw them out. If you have room in your garden let them grow and hopefully you'll have a nice harvest later this summer. If these plants are from heirloom varieties you should get some tasty tomatoes.

    I started some flower and

    I started some flower and vegetable starts indoors and one morning woke to them all eaten. What could have done this? I have looked for worms, but none around. No bugs of any kind to be seen.

    Hi, Bradford, our condolenses

    The Editors's picture

    Hi, Bradford, our condolenses for your seeds. It sounds like dampening off. Even in the best soil, this rot can happen: the seedsling just disappear. Some sources recommend having a blower on them (a fan is just too powerful). Heat lights might help, as they promote drying. At this point, consider it a valiant attempt and put it behind you—and go out and get some seedlings and get growing! You can still have a fabulous harvest.

    hello This year if my first

    hello This year if my first year gardening and me and my father decided to grow multiple types of flowers from seeds and use paper pots and potting soil, we lightly water them every day and we make sure not to over water them, we occasionally taken them outside on nice days to get some sunlight and oxygen, we use stardarnd light bulbs and keep them next to a window when they are inside. The flowers have sprouted into stems and they looked great for a while until the steams either started to die, slouch, or just not bloom into flowers? my dad told me he heard that this could be "stemming" where they grow a little and die?
    is there anything I can do so save these flowers? please help
    thank you!!

    One of my indoor seeds

    One of my indoor seeds recently sprouted but 95% of the others have not Yet. It has only been about 3 days since planting. Should I remove the plastic cover and move them into the sun or wait until more have sprouted?

    Do no remove the covers until

    The Editors's picture

    Do no remove the covers until the seeds have sprouted. There is more advice above.
     

    I.started my seed indoors

    I.started my seed indoors yesterday march 24 was that too late to start the seeds?

    Hi Stacey, It depends on

    The Editors's picture

    Hi Stacey, It depends on which vegetable and where you live. Here is a personalized planting calendar that will give you dates for starting seeds indoors and outdoors for your location, based on your frost dates: http://www.almanac.com/gardeni...
    Hope this helps!

    Hi, Stacey, It's not possible

    The Editors's picture

    Hi, Stacey,
    It's not possible to know the answer to that question without knowing, for starters, where you are. In starting seeds, your goal is to have them ready to plant safely after the last frost in your area. Anyone can only estimate this event, based on historical weather patterns. To find the average date of your last frost, see here:
    http://www.almanac.com/content...
    For the frost date in your area, put in your zip code, and when that date approaches, be aware of local current and expected weather conditions. (The dates are averages, not absolutes.)
    For more advice on how to make sure your seedlings succeed, see the advice above.
    Best wishes for a bountiful harvest—
     

    Help! I started my seedlings

    Help!
    I started my seedlings indoors about 4 weeks ago. There was not enough light and now they are about 3 inches tall and leggy. Should I start over or if I correct the lighting will the seedlings fill out?

    Hi Cindy, Some seedlings

    The Editors's picture

    Hi Cindy,
    Some seedlings start out by growing tall before getting more leaves. Move the seedlings to a spot with more light. You can also start some new seedlings as a backup. Good luck!

    I have covered my ground with

    I have covered my ground with plastic do you keep plastic down for the cucumber area

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