Why Soil Blocking Is the Best Way to Grow Seeds
Although the practice of making solid blocks of soil for growing seeds is not new (it may be over 2,000 years old ), soil blocking has gained popularity in the last few years. It’s a simple process: you form blocks of pressed seedling mixture, lay them out on a tray, and then plant them. This works the same as starting seeds in a plastic seed tray, without the tray. Using less plastic is just one benefit: the real reason people love soil blocking is because it creates seedlings with incredibly strong root systems without being root bound. The air around the block acts as a trimming mechanism; the roots grow to the edge of the soil and then stop. The roots hold the soil block together and can be easily planted into a pot to continue growing inside, or transplanted directly into the garden.
Disadvantages of ground blocking
To make seed blocks, you need soil that compresses and holds together well, most often peat. Peat, a by-product of bogs and swamps, is controversial because its collection has a huge environmental impact . Some people have had success with other materials such as coconut coir, but I am not one of them. I tried coco coir for several years in a row, but suffered from lack of germination and blocks falling apart, so I returned to seedling mixtures with peat.
The other major downside to soil blocking is the actual blocking: it’s a pain in the ass. In my first year, I was inspired by one of my gardening mentors, Meg Cowden of Seed to Fork , who talks about the calm and meditative nature of lockdown . Now I see blocking as an inevitable evil that takes a lot of energy and soil every year. However, the results speak for themselves. Soil blocks perform exceptionally well in seed tray tests.
Step One: Buy a Soil Blocker
The first thing you will need is a soil blocker. There are all kinds of blockers on the market now, and many of them are inexpensive. Blocking soil is similar to making a sand or snow castle: you pack the soil tightly into a cube; the soil blocker compresses the cube and helps it spit out. Soil blockers come in a variety of sizes and designs. There are mini blocks that measure about an inch (for flowers) and maxi blocks that measure four by four inches. But most people will want to start with two-by-two-inch blocks . A basic blocker throws out four of these blocks at a time.
Step two: the right seed mixture with the right moisture level.
Next you will need soil. Different types of plants at different stages of development need different soil. When starting seeds, you need a seedling mixture that is nutrient-free, holds moisture well, and has fine particles so it can be compacted into seed trays. This is ideal for blocking seeds if peat or coir is also included in the mixture. Use more soil than you think you will need because by squeezing the soil to make a block you are using more soil than using seed trays. I managed to make 100 blocks from a 12 liter bag.
Empty the bag into a trash can or other waterproof container and mix it with water. You need to use about three times as much water as soil, adding it slowly and stopping to mix the water two to three times. Soil can absorb absurd amounts of water; you want the soil moist but not wet. Take a handful of the mixture and squeeze it in your hand. Does it stick together? If yes, then you have enough water. If not, add more until it works.
Step Three: Prepare a tray for the soil blocks.
The blocks will live on a tray, and it doesn’t really matter what kind of tray, as long as it can hold about an inch of water and is waterproof. If you were using seed trays, they would still need something to sit on, like a bottom tray, so you probably have something on hand. I have seen installations with standard 1020 trays and installations with cafeteria trays . The blocks are placed next to each other, so the tray 1020 can hold 50 blocks. A dining tray, depending on its size, can hold much more.
Step Four: Set Up Your Dice
Before we start making blocks, you need to set up your blocks. When you plant seeds, you must plant them at the correct depth depending on the type of seed. For example, sunflower seeds are buried very deep, while carrot seeds are located close to the soil surface. The seed blocker has different indentations that you can add to the blocker and these will make corresponding indentations in the soil block to make it easier for you to insert the seed.
Step Five: Start Blocking
Now let’s move on to the actual blocking. Again, if you’ve ever built a sandcastle, this won’t seem all that unusual, but the technique does require some skill. While holding the blocker upright, dip it into the seedling mixture over and over again, rocking it back and forth until you reach the bottom of the container. In this case, the soil enters the blocker. Turning the blocker left and right, pressing it to the bottom of the bunker, compresses the soil. After several passes, lift the blocker upside down and make sure all four chambers are full. If that’s not the case, keep passing, or you can just keep the blocker upside down and jam the dirt in there with your other hand.
Step 6: Line up the blocks on the tray.
To distribute blocks, go to the tray in which they will be stored. Press the lock onto the tray by slowly pressing the handle and lifting it up. This process should result in four perfect blocks, but this doesn’t always happen, and if a block looks like it’s about to fall apart, pick it up and throw it back in the bin. It’s just soil; it will fall apart. At this stage the blocks are fragile, but not immobile if you are careful.
Now start over and distribute more blocks. Continue until you have as much as you need on this tray. At this point, it’s time to plant the seeds. Treat each block like a cell in a seed tray. Plant one or two tomato seeds, a bunch of carrot seeds, or one pumpkin seed. Cover the seed with additional seed mixture.
Step 7: Fill in the Blocks
From this point on, the process is similar to growing in seed trays. The soil needs warmth, so place the tray on a heated seed mat. The blocks need water, so every few days you should fill the tray with enough water to completely cover the bottom of the tray. The blocks will absorb water and remain moist, allowing germination to occur. The seeds need moisture, so cover the blocks with a plastic dome to ensure adequate moisture. Finally, the cubes need light, so make sure there is enough light on the tray, especially after the seeds have sprouted.
The seeds will grow as they do in the seed tray and at some point will become too large for the blocks. Along the way, you will need to select one sapling per block and cut the other one. You can plant the blocks in containers or paper pots, or plant the blocks directly in the garden if it is not too early. I usually transplant the seedlings after a few weeks and they stay in four-by-four inch pots until it’s time to plant them in the ground. Blocks that for some reason do not germinate can be recycled for the following year by simply tossing the block back into the container with the seedling mixture.