What I Love About Starting Seeds With Soil Blocks

On By durhammastergardenersIn Uncategorized

By Marcia Kirinus, NC State Extension Master GardenerSM volunteer of Durham County

I began seed blocking after scouring the internet for an efficient seed-starting method. By chance, I stumbled upon this technique, and I was immediately hooked. It’s smart and straightforward. The seed blocker resembles a ravioli maker, but instead of pasta, it’s filled with a fine seedling mix.

(Left to right) The soil block tool; side view and from the bottom. Filling the the soil block tool with seedling mix. (Image credit: Marcia Kirinus)

How to Use the Soil Block Tool

After loading the blocker with the seedling mix, you press out 40 small blocks, each measuring 3/4.” Then, you place one seed on top of each block. The soil block becomes its own container, eliminating the need for plastic pots. This method can be used for various seeds, including flowers, vegetables, herbs, and potentially shrubs and trees, though I haven’t tested it for those yet.

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(From top to bottom, left to right) 1. Two different size soil blocks. The smaller one I use with most seeds. The larger one is used for larger seeds such as green beans and sunflower. 2. A tray of 40 basil plants of different varieties. 3. A close up of a single stock plant (Matthiola incana); note the beautiful root structure. 4. Seeding eggplant. The block on the left is completely and lightly covered with vermiculite. (Image credit: Marcia Kirinus)

Advantages of Using a Seed Blocker

Cost Effectiveness

  • Eliminates the need for plastic pots, saving both money and space.
  • Ensures precise seed usage, reducing waste from over-seeding.
  • Requires only the purchase of seedling mix and seeds after acquiring the tool.

Efficient Use of Space

  • Soil blocks serve as their own containers, saving space compared to traditional pots.
  • Maximizes space under grow lights, enabling more seedlings to be started simultaneously.
  • No storage needed for plastic pots

Enhanced Germination and Growth

  • Seeds germinate quicker due to the small block size.
  • It produces sturdy, robust plants as the roots are air pruned and ready to pop into the ground.
  • There is little to no transplant shock.
  • The seedlings are uniform in size.

Environmental Benefits

  • Eco-friendly by reducing plastic waste from pots.
  • Reduces the amount of seedling mix needed, minimizing environmental impact.

Convenience

  • Easy transplanting directly into the garden once seedlings reach the appropriate size.
  • Saves time on thinning seedlings and transplanting into larger containers.

Side Benefits

  • It is a satisfying meditative task. You really get to study each seed type because you are handling one seed at a time at a close range.

Disadvantages to Using a Seed Blocker

  • It can be challenging if you’re very busy and unable to water or tend to the seedlings daily. The small blocks dry out quickly, risking loss.
  • The same applies when they’re ready for transplanting; you don’t want them too big, where roots entwine and they become leggy. There is a learning curve to getting this right.

Additional Seed Germination Tips

  • Some seeds require light for germination; research the needs of your seeds. Cover them lightly with vermiculite if they need darkness to germinate.
  • Maintain an air temperature of 65-70°F for cool-season plants like kale, lettuce, broccoli, calendula, and Sweet William. For warm-season plants like tomatoes, peppers, zinnias, and sunflowers, aim for 70-80°F.
  • Proper watering is crucial; avoid overwatering to prevent the growth of algae, which can attract fungus gnats and shore flies. Let the tray dry out between waterings, but don’t allow the seedlings to wilt.

Resources and Additional Information

Check out Michigan State University Extension’s site for a detailed trial on the effectiveness of soil blocking with tomatoes.

https://www.canr.msu.edu/news/impact-of-soil-blocks-on-yield-and-earliness-of-six-tomato-varieties.

For detailed information on how to make your own seedling mix, see Penn State Extension’s Making Soil Blocks.

https://extension.psu.edu/programs/master-gardener/counties/susquehanna/penn-state-master-gardener-articles/making-soil-blocks.

Utah State University Extension offers a great online video with step-by-step instructions on how to make seedling mix, use the soil blocking tool, and start seeds indoors using this method.

https://www.youtube.com/watch?v=JiLGOfm0Z-g

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