Soil Blocking: A Better Way to Start Your Seeds Off Right

Skip all the little plastic pots and get healthier seedlings with soil blocking.

When starting seeds indoors, skip the little pots and single-use plastic clogging landfills by using a technique called soil blocking. Besides eliminating waste from the seed-starting equation, soil blocking will result in stronger seedlings that resist becoming root-bound. Less waste, healthier plants? Now, that's some major garden goals! Here's how to make and use your own soil blocks for starting seeds.

What Is Soil Blocking?

Soil blocking is a simple seed-starting technique that involves compressing a specialized soil mixture into cubes. The free-standing blocks of soil have increased oxygen exposure on all sides, allowing roots to grow vigorously without confinement. Not only do your seedlings end up with healthier roots, but they also don't suffer transplant shock like other pot-grown starts do.

Investing in a quality soil blocker, also called a soil block maker, is key to your seed-starting success. These devices come in a number of sizes, typically making ?-inch to 4-inch square blocks. Depending on the amount of space you have available, you might consider a system that uses different-sized soil blocks that work together, allowing you to transfer smaller blocks into larger ones as your seedlings grow.

Soil Blocking Recipe

Creating a soil mixture rich in organic matter with excellent water retention and good drainage might sound impossible, but can be achieved quite easily when you mix your own blend. There are a lot of different blocking recipes out there, so feel free to experiment with what works best for your growing climate and conditions. Potting soil alone won't work for creating blocks; you need a mixture of peat, compost, soil, and sand or perlite to retain both shape and moisture. The base soil block recipe I like to use, which makes about a gallon of dry mix, is inspired by a mix in Eliot Coleman's book, The New Organic Grower:

Soil Mixture:

• 6 cups sustainable peat or coco fiber

• 4 cups coarse sand or perlite

• 2 cups garden soil

• 4 cups compost, screened through mesh

• small handful of garden lime (optional)

• small handful of organic 4-4-4 fertilizer

1. Mix everything together well.

2. Scoop the desired amount of soil mix into a flat-bottomed utility tub, keeping in mind that the depth of the mixture in the tub must be deeper than the soil blocker itself.

3. Add enough water so that the mixture has the consistency of wet cement. If your mixture is too wet, the blocks will have trouble keeping their form.

How to Make Soil Blocks

Press the blocking tool into your soil mixture, giving it a good twist before lifting up. Make sure that soil has filled each cell in the mold before gently extracting the cubes and setting them ? inch apart in a tray. A standard flat seedling tray works well for holding soil blocks; just be sure the tray has drainage holes in it to avoid standing water. Give your soil blocking tool a quick rinse between each extraction to keep block shape uniform.

Related: The 11 Best Seed Starting Trays of 2024 to Help Kickstart Your Garden

Once you've created all the soil blocks you need, place a seed in the small divot created by the soil block maker. As strange as it may seem, do not cover the seeds with additional soil. Just be sure that the seed has good soil contact; use your finger or the bottom of a pencil to gently press each seed against the soil.

Seedling Care and Transplanting

The key to keeping your soil blocks from falling apart is watering from the bottom up. Using a fine mist spray works well while seedlings first develop; however, soaking the blocks in a shallow amount of water or a gentle nozzle spray from the bottom will be your go-to method for watering until transplant day.

Depending on your climate and soil block size, watering needs will vary. It's important that the blocks don't get overly damp, but also don't dry out. Dryer, warmer growing zones, as well as smaller soil blocks, will dry out the quickest. After the first week, you'll get the hang of their individual needs and a routine that keeps them consistently moist.

Related: Build a DIY Seed-Starting Station to Begin Your Garden Indoors

Once your seedlings have several sets of true leaves, they're ready to transplant into the garden. Larger plants such as tomatoes, eggplants, and peppers will need to be established in at least a 4-inch block before transplanting. Some gardeners prefer to "pot up" into a larger container before bringing it into the garden, but it's not necessary.

Carefully place your blocks directly into the garden soil using a trowel. Then water well and apply a layer of compost around your transplants. You'll be amazed how quickly they will take off from there. Here's to stronger, more sustainable seedlings this growing season!

Frequently Asked Questions

How long can seeds stay in soil blocks?

As mentioned before, your seeds need to have several leaves before transplanting. However, keep in mind that you shouldn’t wait longer than 4 or 5 weeks or if there are several visible roots. Plants’ roots don’t like to be “disturbed” and that may compromise their health.

Are there any disadvantages when soil blocking?

Soil blocking isn’t a complex project, but it does require time and effort. This isn’t a disadvantage per se, you just need to make sure you have the flexibility for it. When it comes to plants, some seeds may be difficult to start growing in
certain conditions, especially if you didn’t follow a proper technique.

What kind of seeds are best recommend for soil blocks?

Small seeds such as eggplant, celery, parsley, pepper, or even cilantro or green
onion are perfect for a beginner-friendly soil-blocking project. Corn, carrots,
and tomatoes are also doable, but you’d need a bigger space for them.

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