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

    You can keep the the plastic

    The Editors's picture

    You can keep the the plastic on the ground and cut holes to plant the cucumbers.

    I need help.. First time

    I need help.. First time growing anything ever.. I started tomatoes indoors under t5 high output lights.. They were doing great.. Now all a sudden the leaves r turning black on the edges and in the middle.. Starts out looking like someone put clear coat on parts of the leaves then it turns gold color then turns black brown and gets crispy.. Anyone have any ideas for me I'd be very grateful

    It sounds as if you may have

    The Editors's picture

    It sounds as if you may have a tomato disease called early blight which is caused by a fungus. To avoid this, avoid overhead watering and only water at the base. Make sure plants are spaced farther apart to improve air circulation. If the infestation is heavy, sulfur dust may help protect new leaves from infection. Ask your garden center.

    I started seeds indoors and

    I started seeds indoors and they were doing good. I took them outside and I forgot to bring them in one night and it poured the rain and they got over watered and died. I want to start the seeds over by planting new ones. I was wondering if I could just let the soil dry out and take the plants that died out or if I would have to start over with new soil? I read about plants damping off and it has me worried that that happened because they turned yellow and died. But can I reuse my soil or not?

    Most plants won't die because

    The Editors's picture

    Most plants won't die because of one night of rain.  If the soil is stays wet, however, they could certainly yellow and die. We're not clear that they have a disease.
    If you can get the soil to dry out, you need to bulk it up by mixing in plenty of organic matter; the rain washes away nutrients so you need to add those nutrients back to the ground.
    If poor drainage and waterlogging are a consistent problem, you may need to rethink your planting site, the type of plants that you grow, how to add drainage, and/or a raised bed option.

    I have 2 questions...I want

    I have 2 questions...I want to plant all of my vegetables, flowers and herbs by the moon phase and sign. #1 When starting seeds indoors, would go by the phase/sign favorable for that particular plant or is that only for sowing directly into the ground? #2 When transplanting my seedlings into the ground (I know favorable signs are Cancer, Scorpio and Pisces), do I follow the moon phase favorable for that plant as well or is that only for seeds? Thank you!

    Hi Crystal, It's great to

    The Editors's picture

    Hi Crystal, It's great to hear from you!  Gardening by the Moon applies to both seeds and transplants.
    The dates are related to whether the plant bears its crops below or above the soil.
    We just added our Gardening by the Moon calendar to make planting dates easier! See below page--and then click on your region:
    http://www.almanac.com/content...
    All the best! The OFA staff.

    started seeds far too early

    started seeds far too early .. tomato
    how do I slow them down a bit about 3 inches high .look great.... pepper about 1 inch high ..slower growing .. look great .. they may be O . K .
    .... urgent .... worried ....

    It's fine to transplant the

    The Editors's picture

    It's fine to transplant the seedlings into bigger containers that can be put outdoors during warmer days and moved back indoors at night.

    I started my seeds in an

    I started my seeds in an indoor greenhouse and the cukes, melons, and squashs are 6inches tall already and its going to be another month before I can plant them in the garden. Can I cut them down without them dying?

    I live in Sudbury Ontario

    I live in Sudbury Ontario Canada. I started scarlet runner beans indoors three weeks ago, they are now a foot tall and due to our exceptional winter, I will not be able to plant them for at least two months. Should I be cutting them back? They are growing so fast you can almost see them grow. April 2 2014

    You could transplant the

    The Editors's picture

    You could transplant the seedlings into bigger containers that can be put outdoors during warmer days and moved back indoors at night. The only problem may be space (the runner beans grow really tall and need a trellis).

    Thank you for your response.

    Thank you for your response. I have already moved them into bigger pots and have staked them with bamboo, I guess I just have to hope that they survive until I can plant them.

    I started some tomato plants

    I started some tomato plants indoors and have some seedlings. Unfortunately they are yellow. What did I do wrong? Is there anything I can do to save them or the pots that haven't germinated yet? Any help would be appreciated.

    It could be related to

    The Editors's picture

    It could be related to over-watering, but it could also be a disease called Fusarium Wilt which affects seedlings; the symptoms are yellowing and wilting lower leaves.  Take a sample to your local garden nursery or cooperative extension as it is hard to diagnose online.
    The most practical way to control Fusarium Wilt is to plant disease-resistant tomato varieties. Ask you local nursery.
    Spraying with a copper-based fungicide such as Kocide or Fungus Fighter may help in some cases but usually the plant will need to be pulled. You really want to avoid replanting tomatoes in that diseased soil for at least two years, some say four years. Crop rotation is always essential.
     

    Thank you for the advice. I

    Thank you for the advice. I stopped watering and they're looking ok, but now I'm dealing with moldy peat pots. I'm learning as I go!

    I live in WNC and would like

    I live in WNC and would like to start my tomato plants today, in peat pots. I have many different kinds of heirloom tomato seed. The signs are in the reigns today but the full moon is waning. What to do? My mom always planted by the signs.

    We recommend to plant and

    The Editors's picture

    We recommend to plant and transplant when the Moon is in a fruitful sign (Cancer, Scorpio or Pisces). It is also suggested that you plant veggies that bear above ground crops in the light of the Moon (from the day the Moon is new to the day it is full). Feb. 20-21 are Scorpio if you want to follow the signs. If you want to wait for a waxing Moon it will be new on March 1.

    Thank you for your response!

    Thank you for your response! I had already planted 7 peat pots with tomato seeds. I will definitely follow your advice and come next light moon, I will plant more. Thank you again.

    Hello! I am a new gardener.

    Hello! I am a new gardener. I've been composting for about 18 months now and I've been doing a lot of research at my local library. Needless to say, I was so excited to actually begin planting my asparagus seeds indoors last week. I know asparagus takes at least one season to be harvestable, but it's been a week and I haven't had any germination. I used a 60/40 Miracle Gro potting mix (I'll use seedling mix next year)/compost mixture. I put a "hot house"--a shallow under-the-bed storage unit--over my seedlings only to grow mold! I sprinkled some cinnamon on my seedlings and replaced the "hot house" today. So, all in all, I haven't had any germination. The plants are being grown in my basement. I don't the exact temperature of my basement, but I'm assuming it's about 65 degrees. Should I just be more patient? Does asparagus take a long time to germinate? Sorry this post is long. I just want to start growing food for my new family! Thanks!

    Asparagus is slow to get

    The Editors's picture

    Asparagus is slow to get going from seed. It can take three weeks before the seeds germinate. The seeds should be planted about 1/4-inch deep using a sterile seeding mix for best results.

    How do you get rid of

    How do you get rid of earwigs? Over the past 2 years I tried to grow lettuce but at harvest they were full of drawings.

    You can trap earwigs in

    The Editors's picture

    You can trap earwigs in rolled up newspapers or in old tuna fish cans baited with fish oil or vegetable oil. Place traps near the problem areas and check them each morning. Shake live insects into a pail of soapy water to kill them.
    Converting the backyard to a dry, sunny environment with few hiding places will also help control earwigs. Remove any shelter sites, prune low-growing bushes, avoid growing the earwigs' favored food plants, and destroy moss and algae. Avoid overwatering and don't use thick organic mulches.
    A variety of insecticides available labeled for earwig control. Talk to your garden center. Read the label to determine the proper sites and vegetable restrictions.
    We appreciate your interest in The Old Farmer's Almanac and our web site.

    Last year...WOW...sluGs...! I

    Last year...WOW...sluGs...!
    I live in north western Washington state...what in the world to do about slugs ...I've tried beer in a bowl...salt at every strategic point...it makes a huge problem for gardening...but keeping them off of my sliding glass door and windows would be nice...they even slip in under the threshold from time to time?
    Please advise...
    Thx, Serena

    For slugs use a small, fairly

    The Editors's picture

    For slugs use a small, fairly shallow dish. Put oil (canola, corn, vegetable) in the dish, about 1/2 cup or so. Then pour some soy sauce in the dish. The slugs are attracted to the soy sauce and once they get in the dish they can't get out because of the oil. Here are a couple of more tips. Spread wood ashes, crushed eggshells, or copper sheeting around the area where you see the slugs. You can also try this spray: Stir together 1 quart of water, 1 tsp of liquid dish soap and a pinch of cayenne pepper. Do not dilute before spraying.
    Also, you might enjoy our video, "The Slug Board Game" (humor required) here: http://www.almanac.com/video/g...

    This will be my first year

    This will be my first year attempting to grow herbs indoors in a small apartment in Newark, NJ. I have the perfect spot picked out for my 'babies' but I was wondering if I needed to invest in a heating mat, as I'd like to start germinating in mid-February.

    A heating mat isn't

    The Editors's picture

    A heating mat isn't necessary, but it does help to encourage germination, so seeds sprout faster, which is especially helpful for those plants that have a long germination period. Some herbs may prefer different soil temperatures than others; check the seed packet or catalog description. There are also home-made versions that provide bottom heat as well; some people set their containers on top of the refrigerator, which provides a little warmth. A heating mat specifically made for seed starting provides more control over the soil temperature.

    How do you get rid of the

    How do you get rid of the mold/mildew on the plants?? I just noticed my flats are covered in it! We are going to be moving them outdoors soon. Should they even be moved or will it infect everything else?

    You should physically scrape

    The Editors's picture

    You should physically scrape off the mold/mildew and then try sprinkling your flats with ground cinnamon.

    Why do you recommend not

    Why do you recommend not using potting soil? I live in the Midwest and have used potting soil for the past couple of years and didn't seem to have a problem using it. Why would using soilless peat moss, mixed with equal parts vermiculite and perlite be better, besides allowing oxygen to flow?Thanks!

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