What is Soil Blocking?

Soil blocking uses metal molds to create cubes of soil for starting seeds and transplanting. Soil blocking is a technique for starting seeds indoors that offers a lot of advantages.

• It doesn't require cell packs or pots, so there's less plastic waste.
• It also promotes a vigorous, robust root system to give your seedlings a strong start.

Sizes of Soil Blockers

There are different sized molds available.

• The smallest is the 20 Soil Blocker which creates twenty 3/4-inch cubes. These are great at starting a lot of small seeds as well as those that benefit from bottom heat. The small size of the cube makes a heating mat super effective at warming the growing medium. This can increase germination rates and speed up germination time.

• The next size up is a 5 Soil Blocker that forms five 1 1/2-inch square blocks. These can be used to start many types of vegetable, flower and herb seeds.

• We then have the classic 4 Soil Blocker that creates 2-inch cubes of soil. Here you have two options.

  • One, you can use the rounded dibbles to make blocks with a small indentation for starting all types of seeds.

  • Or two, you can attach the square dibbles if you wish to transplant the smaller 3/4-inch cubes into these larger blocks. For example, I start my peppers in the small cubes, transplanting them into these larger 2-inch cubes once they've developed several sets of true leaves.

• The 1 Soil Blocker is the biggest mold, making 4" cubes. This heavy duty blocker makes large soil cubes perfect for big seeds like sunflowers, winter squash, pumpkins and gourds. Or you can use it to pot up the two inch cubes into a larger volume of soil.

Growing Medium for Soil Blocking

Okay, now that we've learned more about the various sized molds, let's look closer at the ideal growing medium when soil blocking. You can use a high quality seed starting mix or make your own through ingredients like coconut coir, perlite, compost and organic fertilizers. The key to creating sturdy soil blocks that hold together for weeks or months is moisture. When forming the blocks, the growing medium should be well saturated. I know it's ready when it looks like brownie batter or wet cement.

How To Make Soil Blocks

When I'm ready to make soil cubes, I start by gathering all my supplies: the different soil blockers, a flat bottom container which makes soil blocking easier, the growing medium which I've already pre moistened, trays to hold the soil cubes. I've got a butter knife to scrape the bottom of the soil blockers. I've got a container of water to rinse them clean in between use and, of course, seeds, labels and markers.

My growing medium is now ready to go, so I'll start to make cubes by filling the soil blockers. I start by pushing the blocker into the soil, pressing it down several times. I use my hand to pack more soil in. You want each cube to be well-compacted. Once it's full, use the side of the container or a butter knife to scrape off excess soil.

Place the filled soil blocker on the tray and push the spring loaded handle to release the blocks and repeat. You might find it helpful to rinse your soil block or off in a container of water in between each set of blocks. If there's soil left in the mold, it can cause the cubes to stick. A quick rinse solves this problem.

Seeding Into Soil Blocks

Once your tray is full, it's time to sow the seeds.

I plant 1 to 2 seeds per block, sowing them to a depth that is just two times their diameter. Add labels to keep track of your plants and varieties. You can use toothpicks with little flags made of tape, you can draw a diagram of the tray or use tape along the edges of the tray.

Growing On

As the seeds germinate and the plants grow, I leave my grow lights turned on for about 16 hours each day. Keep an eye on the moisture level of the soil cubes. When the top millimeter (about 1/32 inch) of the cube has dried, I bottom water. Bottom watering helps the cubes stay together. If you top water, the pressure of the water from a watering can can cause the cubes to crumble.

When To Pot Up (Or Transplant) Your Soil Blocks

When you see roots growing out of the bottoms of your soil cubes, it's either time to transplant them into the garden or if it's too early to do that yet, you can pot them up into a larger size soil cube. The 3/4-inch cubes are moved into 2-inch diameter cubes and the 2-inch diameter cubes are moved into the 4-inch diameter cubes. It's quick and easy.

I hope you enjoyed this video on making and using soil cubes for seed starting.

Happy growing!

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