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

    Growth stops

    I have grow lights in my house which I keep at least 70 degrees. The seeds germinate quickly and well, but then there is not much more growth. I tried adding a diluted liquid fertilizer. This has been true of basil, broccoli, cauliflower, parsley, peppers, etc. The lights are a few inches above the plants, but they just don't grow more than a couple inches.

    Seedlings

    The Editors's picture

    Seedlings spend most of their first weeks putting down roots, so it’s not unusual for growth to appear to slow down after the initial burst of leaves—in reality, the seedlings are just doing more growing under the soil. However, stunted growth can also be a sign that they’re lacking something—usually light or root space. Once seedlings have a few true leaves (these are the leaves produced after the initial “seed” leaves that have a different look to them), you may need to transplant them to slightly larger containers to give them more room to grow.

    seedling video

    I found these videos very helpful & interesting. Showed me things I didn't know about. I hope I get better luck in planting this year. Thank you

    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?

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