Updated: Apr 17
Now that we have determined WHEN to start seeds indoors lets talk about HOW to grow plants from seeds, step by step, and specifically about how to plant seeds indoors with a goal of later transplanting them outdoors to the garden.
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1. Choose the Right Container or Pot
You may think it does not matter what container or pot you start your seeds in, but I disagree. Using the right container or pot to grow your plants from seeds plays an important role in the health of the plants. If your container is too large, too deep or has poor drainage your plants will be weak and susceptible to a number of issues including rotting off, disease and mold.
As a general rule, the smaller the seed the smaller the container. Look for a container that is around 1.5 inches deep to start small seeds in and sow them in rows 1 inch wide. This way you can use the blunt end of a pen or Sharpie to lift the rows and gently break seedlings apart to transplant. Larger seeds such as sunflower, nasturtium, cucumber and squash, do well planted in plugs or 2 to 4 inch containers - planting one seed per pot.
Once seeds have germinated, make sure there is sufficient drainage on the bottom of your plant container to allow the surface of the soil to dry out between waterings.
2. Use High Quality Potting Soil
It is important to choose a high quality potting soil when growing seeds indoors. When choosing potting soil, look for one that is sterile and has both peat moss and vermiculite (or perlite) in the ingredients. The peat moss enables the soil to retain moisture without seeming waterlogged and causing plant roots to rot, and the vermiculite (or perlite) improves drainage. Most Pro-Mix brands of soil or Sunshine Mix (may be labeled Sungrow) work well for starting seeds.
3. Plant Fertile Seeds
Using high quality seeds should provide you good germination (sprouting) rates. If seeds are not stored properly from year to year or are too old they may not germinate well. If you are purchasing seeds ahead of time, store them in a dry, dark cool place. (I like to store mine in the fridge with silica packages in my seed storing container.)
Check out Zappa Seeds for quality online seed ordering.
4. Plant Seeds at the Correct Depth
Check the back of your seed package to find out how deep to plant your seeds. Some seeds need to be sown on the surface and exposed to light to germinate (ie. celery), others like to be covered in a thin layer of soil and others planted up to 1 inch deep.
Always moisten soil prior to planting seeds and for best success, plant in soil that is room temperature or slightly warmer.
How to Plant Seeds:
To surface sow seeds, set or sprinkle seeds onto the surface of your moist soil and press seeds gently into the top of the soil so that when you water they are not dislodged.
To plant seeds 1/8 - 1/4 inch deep, sprinkle seeds on warm, moist soil; next sprinkle a fine layer of dry soil on top of the seeds; and finally, water gently with lukewarm water (try not to use cold water).
To plant seeds 1/2 inch or deeper, poke your finger or the blunt end of a pen into the soil to make a hole the correct depth (if you are concerned with getting the depth accurate, mark it on your finger or the blunt tool) and press down into the center of the pot.
5. Provide Heat
Most seeds germinate (sprout) best at a temperature of 21 - 25 degrees Celsius (70 - 77 degrees F). If your house is cool, your seeds may benefit from using a heat mat designed for sprouting purposes. (I have never used a heat mat myself and haven't had a problem with germination.) Some people even germinate seeds on the warm top of the fridge!
6. Consistent Moisture
To encourage germination, cover your seed tray or plant pots with saran wrap, a clear plastic lid or keep them inside an indoor greenhouse to increase heat and humidity and to protect seeds from drying out. Remove the cover immediately once you see the seeds have germinated (sprouted). If you are using a heat mat, remove seeds from heat as soon as they germinate.
After germination most plants benefit from allowing the surface of the soil to dry out between waterings. This should happen in 1 to 3 days. If this is not happening, trouble shoot the cause. Are there drainage holes in your plant container? Are you using high quality potting soil? Are you watering too heavily? Is the pot too big for the plant?
Allowing the surface of the soil to dry out benefits your plants by allowing the roots access to adequate oxygen as well as helping to prevent rot, disease, mold and algae.
7 - Plant Seeds at the Correct Time
Refer to the back of your seed packages to find how many weeks prior to your last expected frost you should be starting different varieties of seeds indoors. Seed packages are not always 100% accurate. I keep notes in my gardening journal and adjust my seed start dates based on past years' experience. (You can find my printable seed starting guide as well as dates for when to start your seeds indoors here.)
Some seeds do not do well started indoors. Click here to find out what seeds to start indoors and what seeds should be planted directly in the ground outdoors.
8. Provide Sufficient Light
Lights for starting seeds indoors can vary from using a south facing window (completely possible although you will likely end up with leggy seedlings), broad spectrum grow lights, 40 watt florescent daylight bulbs, or 1800+ lumen and 4000+ kelvin florescent or LED shop lights. (The higher the kelvin number the closer the light is to daylight.) Keep grow lights on for 14 - 16 hours a day and at a height of 6 - 18 inches above small seedlings. Move lights higher as plants grow taller.
9. Transplant as Needed
Watch seedling growth closely and transplant when the height of the plant gets much taller then the depth of the container. Keeping these two fairly close in balance will aid in providing consistent moisture without your plant container becoming waterlogged.
Your seedlings will benefit from using a 10-52-10 fertilizer once a week for the first six weeks or until you see good root development on the bottom of the pot they are planted in. Once you see good initial root development switch to a 20-20-20 for an all around plant fertilizer. If you prefer organic, research alternate methods like fertilizer tea, fish fertilizer, mushroom compost or worm castings.
11. Harden Off Your Plants
Before you transplant your seedlings outdoors you need to harden them off so they don't die of shock with the temperature and light changes. Check out my step by step guide on how to harden off your plants in a week.
If you have problems with seedlings becoming leggy (tall and spindly) check out my post How to Fix and Prevent Leggy Seedlings.
I hope you feel now feel confident on how to grow your plants from seeds step by step. If you have found this article helpful and would like to see more gardening tips and tricks, subscribe to my blog (the bottom of the home page) and follow me on Pinterest, Instagram, Facebook and/or YouTube!