How To Start Seeds Indoors

Learn how to start seeds indoors with these step by step beginner friendly instructions. With a list of all of the supplies you need, and helpful photos to set you up to grow plenty of healthy seedlings for your vegetable garden!

Seed trays all lined up on a patio to be hardened off.

Starting your own seedlings can save you a ton of money if you’re planning to grow a big garden because buying starts at the greenhouse or garden centers can really throw a wrench in your budget!

If you’ve been intimidated by the idea of starting seeds indoors, don’t be! There are definitely some tips and tricks you need to learn, but if you have the right supplies and get on a good watering schedule, you’ll be on the right track!

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A wire rack with grow lights, seed trays and seedlings. It is being used for indoor seed starting.

what do you need to start seeds indoors

supplies

Seed Starting Mix – The seed starting mix you choose will either set you up for success or failure so it’s really important to use a good one! I use Promix mixed with worm castings (1 part worm castings to 5 parts Promix). You can also make your own if you’re a little more adventurous!
Seed Trays – There are so many options when it comes to seed starting trays that it can be really overwhelming! Johnny’s Seeds has a great resource explaining what trays are best for what seedlings, but the majority of plants can be started using 50 cell trays so that’s what I would suggest if you’re wanting to keep things simple. Don’t forget the flat trays without drainage holes to go underneath as well for easy watering.
Heat Mat – While you can get away without a heat mat for germinating seeds, you will get higher seed germination rates with one and waste less seeds in the process. Look for one that fits the shelving unit you plan to use. If you don’t want to start with a heat mat, choose a very warm place in your house instead.
Grow Lights – Look for lights that are advertised as “grow lights” and make sure the length is right for the shelving unit you plan to use. You will need 2-3 lights per shelf depending on how deep the shelves are. I use 3 for my 24 inch deep shelves. I have seen people use fluorescent lights successfully as well, I don’t have any personal experience with them though.
Wire Shelving – Wire shelving works best for seed starting because it won’t be damaged by watering and the grow lights can be hung from the shelves above easily.
Seeds – The fun part! Source fresh seeds from reputable sources so that you aren’t wasting your time and money on supplies for seeds that won’t germinate well! I like Johnny’s Seeds and Baker Creek for high quality organic seeds.

Some gardeners swear by using soil blocks over seed starting trays and one of these years I am going to try it for myself! For more info on using soil blocks, check out the Seasonal Homestead. I do believe both work well, it’s mostly a case of personal preference.

Prepare Seed Starting Mix – Scoop enough seed starting medium to fill your trays into a bucket or tote. Wet the medium down until it is moist but not soggy. (it should not be drippy when you squeeze it, but just hold it’s shape)
Fill The Trays – Fill each cell of your seed starting trays with seed starting mix. Tap the tray firmly on a hard surface to make sure there aren’t any air pockets. Fill the cells to the top but don’t pack them too much.
Sow The Seeds – Follow the directions on the back of your seed packet in regards to timing and depth for each particular seed. Some seeds need to be planted a 1/4 inch deep and covered, others don’t need to be covered at all.
Place On The Heat Mat – Cover the tray with either a clear plastic humidity dome or a piece of plastic wrap. This will help the seeds to germinate and shed their seed coating once they have emerged. Place the thermometer piece into the seed starting mix and plug it in. Set the heat to 78 degrees F.
Once The Seeds Have Germinated – As soon as you see that half of the seedlings have germinated, remove the humidity dome and unplug the heat mat.
Place Under Grow Lights – Immediately place the tray of seedlings under grow lights positioned just a few inches away from the tops of the seedlings. If the lights are too far away, your seedlings will get leggy stretching for the light.
Water – Make sure your seedlings are watered enough, but not too much. The soil mix should dry out a bit between waterings but not dry out completely. Bottom water the seedlings by pouring water into the base tray. Let the soil soak it up and pour out whatever water is left over after a half hour or so.
Fertilize – After the seedlings have developed their first set of true leaves, fertilize with a balanced fertilizer or fish emulsion (diluted according to each product)once a week.
Hardening Off – Raise the lights as the seedlings grow. Once your seedlings are two weeks away from the date they should be planted outside, start hardening them off.

why you should start seeds indoors

Starting seeds indoors gives you a head start on the season as opposed to direct sowing them into the garden.
More budget friendly than buying starts (if you need a lot of seedlings)
There is a wider variety of seeds available compared to what you could find at your garden center.
Oftentimes plant starts you buy carry a disease or pest that you don’t want to bring home to your local garden center.
When you start your own seedlings, you can succession sow certain crops for an extended harvest throughout the growing season.

FAQ about indoor seed starting

When should I start seeds indoors?

Each type of seed has a specific time it should be started indoors to be ready to be planted outside at the best time.

Most seed packets will tell you to start the seeds anywhere from 4-12 weeks before your area’s last frost date (this is an estimated average).

First find out what date that is, and then count back the number of weeks the packet specifies and that will give you the correct time you should start that type of plant indoors.

What seeds are best to start indoors?

You can start most seeds indoors, besides root crops which do best planted directly into the garden.

Do I need grow lights?

Yes. If your seedlings don’t get between 12 and 16 hours of direct light a day, they can grow long and leggy, reaching for the light.

If you don’t have any other option, you can grow decent plant starts using natural light if you start them under a South-facing window.

What temperature do seeds need to germinate?

Most seeds germinate well at a soil temperature 65–75°F (18–24°C). For best results use heating mats to have better germination rates with warm season crops, especially if your seed starting room is cool.

How often should I water my seedlings?

When the seedlings are small, you’ll need to water them about once a week. As they grow, they’ll need to be watered more often. Keep the soil moist but not soggy.

What is “damping off” and how do I prevent it?

Damping off is a fungal disease that will kill seedlings. To prevent it, use clean seed starting containers, make sure there is adequate air flow in the room and bottom water your seedlings.

When the seedlings have their first sets of true leaves, put a fan nearby to help with airflow and strengthen their stems so that they’ll be able to handle wind better when they’re planted outside.

Bottom watering just means to pour water into the tray beneath the cell tray so that the plants can “wick” it up. After a half hour or so, drain out excess water that the plants haven’t needed.

Can I use garden soil To start seeds indoors?

No. Garden soil is too dense for the fragile seedlings and can contain disease. Use a sterile, fluffy seed-starting mix instead.

When do I transplant seedlings to bigger pots?

Transplant into larger containers when they have 1–2 sets of “true leaves” and outgrow their starter cells.

When and how do I harden off seedlings?

Starting 1–2 weeks before transplanting outdoor, gradually introduce your young seedlings to outdoor conditions a few hours a day, increasing time and sun exposure daily. Hardening off is necessary to avoid transplant shock that can cause seedlings to be stunted or die.

Don’t start the hardening off process on a bright sunny, windy day. The best way is to wait for a day that is overcast and calm. Or choose a spot that is protected from the elements like a carport or covered porch.

How To Start Seeds Indoors – Guide For Beginners