Seed Starting Indoors Complete Guide

Starting plants from seed is a relatively easy project if you plan ahead. Planning and equipment needed is important, so here’s some items you will need:


  • Read the back label for instructions on how to plant and when to plant determined by the last frost date in your area.
  • You won’t be planting all your seeds varieties at the same time.
  • Remember the larger the seed the deeper you’ll need to plant the seed.


  • Use a label and put name of seed variety, date you seeded it and the date it should germinate.
  • All the information will be at hand when you need it.

Seed Starting Soil

  • It is important to use sterile seed starting soil because baby plants with baby roots need loose soil to grow.
  • Some recommended organic starting soil would be:
    • Black Gold (Sun Gro) Organic Seedling Mix or
    • Espoma Organic Seed Starter Mix.
    • Both are easily found in your local garden stores.

Water and Spray Bottle 

  • If you’re using tap water that has chlorine, let the water sit overnight to dissipate the water or use distilled water.
  • Avoid softened water, which can contain salt.
  • The spray bottle will be used when watering the seedlings.
  • It’s important that you don’t overwater or allow the seeds to sit in water.
  • Allowing it to be a bit dry is fine.

Bowl For Mixing 

  • You need to mix the soil with water in the bowl.
  • The consistency needs to be moist but not sopping wet.

Pots, Trays and Dome 

  • If you are using last year’s pots, trays and domes, they need to be washed so no disease is transmitted.
  • Pots can be any variety of cell packs and individual pots.
  • The clear dome will keep moisture on the seeds in their trays while germinating.
  • The water tray underneath the seed tray is so water stays doesn’t spill everywhere.
  • Seed-starting kits can be bought that have the pots, trays and dome.

Light Source, Heating Mat and Timer

  • Overhead lights are used once the plants germinate.
  • An overhead light is preferable to window light because stems may lengthen toward the outside light.
  • To germinate seedlings, need a consistent heat under tray.
    • But if you don’t have a heat mat, the germination time will take longer.
  • A timer is needed so the seeds have the necessary light and dark.
  • Make sure your light source can be raised as the seedlings grow taller.


  • Using Vermiculite on tiny seeds that are on top of the soil will prevent the drying out of seedlings.


  • A supplemental liquid, organic or water-soluble fertilizer is good for the seedlings to grow.
    • Fish emulsion, worm casting tea, Espoma’s Grow, Black Gold All-Purpose Fertilizer or Miracle Gro Water-Soluble All-Purpose Plant Food


  • Air circulation is important.
  • A small fan far enough away to create a gentle breeze across the seedlings is good from time to time.


  1. Look at the back of your seed packet.
    1. Read the instructions on planting depth and how many days from your frost date.
    2. Note how small or large the seed is for planting.
  2. Make a label for each seed variety, date seeded and germination date.
  3. Remember to plant only the number of seeds you will need and not the whole packet.
  4. Take the mixing bowl and fill it with seed starting soil.
  5. Mix with some water.
  6. Test the soil after mixing by taking a fistful of soil.
    1.  If the soil is too loose, you may need to add more water.
    2. The soil consistency should be moist but not sopping wet.
  7. Put the soil into the planting pot.
  8. Press down enough on the soil so it’s not tight into the pot, but so there aren’t any air pockets and at the depth you will be planting the seed.
  9. Put in at least 3 seeds per pot, depending on how large your pot is.
    1. After putting seed into the pot, you will be putting more soil on the top loosely and not patted down.
    2. If the seed is supposed to be planted on top of the soil, then put vermiculite on the top and not soil.
  10. After each seed’s variety has been sown, place the pots in their holding tray.
  11.  Use your spray bottle to spray the top of the soil with water enough to thoroughly moisten the soil.
    1. Don’t ever drown the seedlings.
    2. Spray just enough to keep them moist.
  12. Once all your seeds are finished, take the seed trays to their starter home.
    1. This is where you have already set up an overhead light, heat mat, moisture dome and timer.
    2. Seeds will start in the dark with the dome on top, but no light until they germinate.
    3. Lights need to start at the low position and will be raised as the seedlings grow.
  13. Seeds need warmth to germinate.
    1. If it’s too cool, they may germinate slower.
    2. Most seeds germinate at 78 degrees.
    3. The waterproof heating mats works well.
    4. After germination air temperature can be a cooler 65-70 degrees, but not below 50 degrees.
  14. Prior to germination, cover your seed trays with the moisture dome to help trap moisture inside.
    1. You can use a clear plastic bag, but it should be supported so it doesn’t lay flat on the top of the seed tray.
    2. Remove the moisture dome as soon as the seeds sprout.
    3. Once seedlings are growing, reduce the watering so the soil can be partially dry, but not dry enough to wilt the seedlings.
  15. Once the seeds have germinated, you need to put them under the lights for the seedlings to grow further.
    1. For optimal growth they will need 16-18 hours of light per day. 
    2. A timer is beneficial for this purpose.  
  16. When the seedlings get their “true” leaves (usually the 3rd leaf that looks like the mature leaf, not rounded), the seedlings will have used up all the fertilizer in the starter soil.
    1. A half-strength supplemental liquid organic or water-soluble fertilizer will need to be added every other week until transplanted.
  17. Use a fan or circulate the air occasionally otherwise water borne diseases can develop.
    1. After the “true” leaves develop apply the diluted fertilizer every other week.
  18. Once the seedlings become bigger and healthier a new, larger pot will be necessary.
  19. Transplant the plant into larger container with transplant soil or container soil to replace the seed soil.
    1. When the weather is better you will need to gradually get them used to the outside weather and temperatures before putting them into the soil.
  20. Watch your weather so plants can gradually be introduced to the outside.
    1. Putting them outside too early could kill the plant.
    2. Using a cold frame or cover crop fabric is helpful.