How to start seeds with soil blocks

Jess from Earth, March 24, 2023

What are soil blocks?

Soil blocks are cubes of soil you make with a hand tool called a soil blocker to start seeds in. They replace plastic cell trays. They are great for plants because they allow the roots to become air pruned, meaning the roots will naturally stop growing when they reach the side of the block (versus getting root bound in a plastic container). They also reduce the use of plastic trays, and the soil blocker can be reused each year, so it really helps the earth!

Step 1: Gather Supplies

You will need:

  • Soil Blocker (I got mine from Johnny’s Selected Seed)
  • Soil Mix (I use the 512 mix from Johnny’s, you can buy any or make your own! Just be sure it’s for seed starting)
  • A solid container with a flat bottom where you can mix soil and water (make sure it’s big enough to fit the soil blocker flat and move around a little)
  • Cup to scoop out soil from the bag
  • A solid bottom tray to place the blocks on (I like one with an edge so I can water them in the tray)
  • Filtered Water
  • Seeds, Labels, Marker
  • Indoor grow light (I’ll make a post on my set-up soon!)
  • Power strip and timer
  • Seedling Heat Mat (optional, helps with crops like peppers)
  • Fan (optional, but helps make stronger seedlings)

Step 2: Form Blocks

Set up a table where you can work, cover it with newspaper if you are worried about getting messy 🙂

Mix a few cups of soil with filtered water in the container until it’s like mud. Push soil to one side to make a nice solid area of soil to dip the blocker into.

Holding your soil blocker straight over the soil mix, push it straight down into the mix in one motion, filling each cell of the blocker completely.

Carefully pick up the soil blocker full of soil, and set it onto your seedling tray, push the handle straight down in one motion to release the soil blocks onto the tray. Fix any broken blocks by hand.

Repeat until you have enough soil blocks for all of your seedlings, one per plant.

Step 3: Plant Seeds! 🙂

You’ll notice most soil blockers leave a dimple in the middle of each block to place your seed.

Carefully remove one seed from your seed packet and place in the middle of the block, at the depth recommended on the package (or usually twice the depth of the seed size). Cover with a bit of the soil mix.

I like to only put one seed per block because then you don’t need to thin (remove) extra seedlings. Plus I think seeds are precious and it makes me sad to waste any. Just replant any blocks that do not germinate or recycle the soil.

Step 4: Set trays under lights

Now it’s time to set your new soon to be seedlings in their new home, under the lights! Some seeds require light to germinate, and you also want to make sure the second the seedlings pop up from the soil they have light.

You can cover the tray if you’d like to help keep the soil blocks moist, just be sure to remove the cover as soon as the first seedling comes out of the soil.

If you are growing a hot crop, like peppers, using the seedling heat mat under the tray will help speed up germination. Some seeds will not sprout unless it’s a certain temperature.

Step 5: Caring for seedlings

Have the fan ready to turn on once the seedlings start growing, the moving air helps reduce fungus or mold on the top of the soil blocks, and helps strengthen the stems of the seedlings. You can also gently brush your hand over the seedlings each day and blow on them to expose them to what the wind will be like when they move outside.

Keep the seedlings just a few inches away from your lights so they do not have to stretch to reach the light, this will help prevent them from getting leggy (really long stems in between sets of leaves).

I leave my lights on for 12 hours per day.

Check the soil blocks a few times each day. Water them from the bottom with filtered water that is room temperature when they start to dry out.

Here is how I water:

Check out my YouTube Channel @jess_from_earth

If you use Johnny’s mix or something similar, they will have enough food from the soil to grow until you transplant them into their next home. So you will only need to water.

Thank you! Please leave any questions, ideas for new posts, or comments below! -Jess 🙂

Tags: soil block

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