Soil blocks are a game-changer for gardeners and flower enthusiasts looking to simplify seed starting while keeping things eco-friendly. By ditching plastic seed trays, you’re giving your seedlings a healthier start with better root systems and less transplant shock. And, best of all, you’re saving a tremendous amount of space.

Here’s everything you need to know to get started with soil blocks.

What You’ll Need:

  • Soil Block Maker: Choose the size that fits your seeds—the mini 20 blocker is good for tiny seeds such as those for flowers and the medium 5 blocker works well with larger seeds.
20 mini blocker

mini 20 blocker

5 block blocker

5 blocker

  • Mixing Bin: A big tub or bucket to whip up your soil mix.
  • Tray or Flat Surface: To set your blocks keeping in mind to keep seeds of same type in same tray as each variety of seeds have different germination rate.
  • Soil sifter: I use the 1/4 inch mesh size purchased from The Gardener’s Workshop (not an affiliate link).

Soil Block Mix:

There are many different recipes for making the soil block mix, but I like to keep it simple by using my favorite potting mix from the hardware store. The key is to sift the potting mix to cull out large pieces. Sifting out the large pieces helps make the soil block form stay intact. Mix the soil with enough water that when squeezed it drips water but it’s not so soggy that it won’t hold the soil block shape.

How to Make Soil Blocks:

  1. Load the Block Maker: Push the soil block maker into the mix, packing it tightly. Scrape off any extra soil to level it out.
  2. Form the Blocks: Place the block maker on your tray and eject the blocks. Keep them snug but with a little breathing room.

Sowing Seeds in Soil Blocks:

  1. Plant Your Seeds: Drop a seed into the indent of each block. Press seed lightly to ensure good soil contact.
  2. Cover Lightly: Dust a thin layer of soil or vermiculite over the seeds. For light-dependent seeds like snapdragons, skip the cover.
  3. Water Wisely: Mist gently to moisten the seeds without disturbing them.

Nurturing Your Seedlings:

  • Keep your soil blocks damp but not soggy by bottom watering (adding water to the tray) making sure the blocks don’t sit in water.
  • Warmth and humidity are keys to good seed germination.

Potting Up into Larger Soil Blocks:

When your seedlings outgrow their mini blocks, it’s time to give them more room. Here’s how:

  1. Make Bigger Blocks: Use the same soil mix to prepare larger blocks. Larger blocks usually come with an attachment that creates a space the size of the mini blocker so that the mini blocker can just be placed into the space.
  2. Transfer Carefully: Place the smaller block into the hole and press gently to secure it.

Transplanting into the Garden:

  1. Prep Your Bed: Dig holes just deep enough for your soil blocks.
  2. Handle Gently: Lift each block with care to avoid damaging roots.
  3. Settle In: Place the block into the hole, backfill with soil, and pat it down gently.
  4. Water Well: Give the transplanted block a good soak to help it settle in.

Pro Tips for Thriving Soil Blocks:

  • Start small and size up as needed. Tiny blocks are perfect for tiny seeds.
  • Avoid overwatering—too much moisture can lead to algae growth or crumbling blocks.

Soil blocks are a simple, sustainable way to grow your seedlings strong and healthy.