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

Feb 9, 2022advice

Kristin Guy for Better Homes & Gardens on a good way to start your seeds off indoors.

Skip all the plastic pots with this simple technique. Plus, you’ll get healthier plants.

Starting seeds indoors can be an inexpensive and efficient way to fill your garden with plants. However, seed-starting trays and pots require a lot of space, add unnecessary costs, and ultimately end up breaking after one season, clogging landfills with unnecessary plastic. But there is a way to grow plants from seed more sustainably. You can skip the pots and single-use plastic completely with soil-blocking. Not only does this technique help you eliminate waste from the seed-starting equation, but you’ll also end up with 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 involves compressing a specialized soil mixture into cubes for seed germination. 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, they also don’t suffer transplant shock like other pot-grown starts do.

Investing in a quality soil blocker ($20, Walmart), also called a soil block maker, is key to your seed-starting success. These devices come in a number of sizes, typically making ¾ inch to 4-inch square blocks. Depending on the amount of space you have available, you might consider a system that uses different-size 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 ($29, Amazon):

Soil Mixture:

  • 6 cups sustainable peat or coco fiber ($20, The Home Depot)
  • 4 cups coarse sand ($15, Etsy) or perlite ($5, Target)
  • 2 cups garden soil ($9, The Home Depot)
  • 4 cups compost ($6, The Home Depot), screened through mesh
  • small handful of agricultural lime ($6, Ace), optional
  • small handful of organic 4-4-4 fertilizer ($10, Amazon)

Mix everything together well. Then, scoop the desired amount of soil into a flat-bottom, utility tub ($7, The Home Depot), keeping in mind that the depth of the mixture in the tub must be deeper than the soil blocker itself. 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 mold before gently extracting the cubes and setting them ¼ inch apart in a tray. A standard flat seedling tray ($22, The Home Depot) works well for holding soil blocks; just be sure to make drainage holes in it to avoid standing water. Give your soil blocking tool a quick rinse between each extraction to keep block shape uniform.

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.

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 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!


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