It’s official! The 2021 gardening season is underway at Elder Oaks Farm!
Two years ago, we constructed a greenhouse that we purchased online. Our two summer gardens since then have been started completely from seeds with lots of trials, errors, successes, and failures along the way. Since we’ve gotten pretty good at growing our vegetables from seeds, we decided to try something new this year: soil blocking. I’ve been curious about soil blocking for years, and I hate to admit this but I’ve even had my own soil blocker that Doug got me for Christmas TWO years ago (insert embarrassed face emoji here). Up until now, I was too intimidated by the soil blocking process and never took the time to learn about it. A few months ago, I decided that 2021 was going to be the year that I learn how to soil block, and I am hoping that I will never look back. In this blog post, I’m going to share what I’ve learned so far about the actually not-so-intimidating process and also how we completed our first round of soil blocking last week. If you are interested in soil blocking but haven’t taken the time to start learning, or if you just want to learn about some really cool gardening stuff, read on!
First things first. Soil blocking is a method of indoor seed starting in which compressed blocks of soil are made using a soil block maker. Soil block makers are spring loaded tools that compress soil blocking mixture into formed soil blocks. The soil block maker also makes a small indentation in the top of the block for placement of one or two seeds.
A soil block is exactly what it sounds like: a single stand-alone block of compressed soil. Each soil block is both the container and the growing medium for one seedling, and the blocks are composed entirely of soil block mix and have no true walls. When the soil block is first made, it is held together only by the soil block mix ingredients. Once the seedling in the block emerges, the roots will quickly fill the block and the block will become much more stable. Since soil blocks have no walls, the roots fill the block to the exterior edges and stop growing – a phenomenon known as “air pruning”. Knowing that the roots can’t advance any further into the open air, the root system creates secondary roots that branch out and grow until they also hit the air. This continues until the seedling forms a well branched system of roots in the soil block and all of the air pruned edge roots of the seedling remain ready for rapid outward growth once transplanted into the garden. In contrast, when a seedling is grown in an enclosed container such as a cell tray or a pot, the roots will start to circle instead of branch when they reach the edges of the container. Seedlings with roots that are circling the growing container are referred to as being “root bound”. Once the root bound plant is transplanted, it takes time for the plant to stop growing its roots in circles and to start growing its roots in branches. The roots of plants grown in soil blocks will immediately start growing outwards into the surrounding soil due to air pruning.
The Benefits of Soil Blocking
- Decreased Transplant Shock. Soil blocking is an alternative to using plastic pots for seed starting, and it effectively prevents roots from encircling a container during growth and becoming root bound. When a plant is root bound, it will struggle to acclimate during transplantation. Seedlings grown in traditional plastic containers often appear wilted and stunted after transplant due to the wounding of their roots and the trauma of transplantation – a sad occurrence known as transplant shock. Soil blocked seedlings that have been air pruned acclimate quicker to the garden soil once transplanted, and will start out healthier and grow faster versus root bound plants. When it is time to transplant a soil blocked plant, the roots won’t be interfered with or damaged. Less disruption of the roots means that transplants establish quicker and seedlings are less prone to transplant shock. Soil block seedlings are also more vigorous as their root systems develop much quicker than those of seedlings grown in conventional plastic containers.
- Ease of Transplantation. When it comes time to transplant, soil blocked seedlings take much less time to transplant because you will just take the soil blocked seedling, dig a hole, and put it into the ground. No digging the seedling out of a container and trying to salvage the root system. And no separating multiple seedlings from single cells of propagation trays (can I get a hallelujah?!). Simply take the soil blocked plant and stick it in the ground. An additional bonus is that many soil blocked seedlings don’t require re-potting.
- Reduction in Plastic Use. Since the soil block functions as both the container and the soil for starting and growing seedlings, soil blocking reduces the use of plastic containers by default and also provides a promising alternative to plastic. For people who grow large amounts of plants, there is inevitably a large amount of plastic waste that is generated from pots, flats, trays, and containers. With soil blocking, there is no need to purchase new plastic containers or sterilize and reuse old containers each year. Although soil blocking still requires some sort of plastic tray to house and water the blocks, the vast majority of seed starting plastic can be reduced and recycled.
- Ease of Storage. Soil blockers take up next to no storage space, whereas it is not uncommon for gardeners to have gigantic disorganized piles of plastic propagation trays and containers. Plastic containers have to be stored somewhere and, in our experience, are virtually always a jumbled mess no matter how well they were originally organized. They take up a ton of space either in the greenhouse or in the shed, and if they are stored outside you better count on the wind scattering them around your yard at least once. But probably more than once. Ask us how we know.
How to Soil Block
Supplies needed for soil blocking: Soil block maker in the desired size, soil block mix, trays, a few buckets, seeds
If you’ve decided that soil blocking is for you, the first thing you need to do is purchase a soil block maker. I received my original soil blocker as a gift, but I also bought a backup soil blocker that is unofficially my mom’s blocker. There are multiple different sizes of blockers ranging from ¾ inch to 4 inches. Both of our soil blockers are standard 2 inch blockers.
The next thing you need to do is decide whether you are going to purchase or make your own soil blocking mix. This was hands down the most intimidating part of the whole process for me. I scoured the internet looking at multiple soil blocking mix recipes only to get more and more confused and overwhelmed. I thought about just buying a bag of premade soil blocking mix, but the shipping was outrageous and I couldn’t find any soil blocking mix locally, so I quickly dismissed that idea. Through my newfound soil blocking research, I found that many people follow Eliot Coleman’s soil block recipe. Although his method seems very tried and true, it also seemed way too complicated for me, so I continued searching. I found a simpler and more straight forward soil blocking mix on the Seed to Fork soil blocking blog post, but I was still overwhelmed. Most of the soil blocking mix recipes that I found called for a mix of peat moss, sand, lime, perlite, various fertilizers, compost, and topsoil. Although that really isn’t THAT long of a list, I was still in search of something simpler and more cost effective for us. After all, we have bags and bags and bags of organic potting soil waiting to be used that I was not willing to waste. I finally came across a blog post that suggested using a 50/50 mixture of peat moss and potting soil. Bingo! Now that was a recipe that I could handle!
A little bit about soil blocking mixes
In order for soil blocks to stay together, a specific soil blocking mix must be used. The main difference between soil blocking mix and regular potting soil is the amount of perlite. In soil blocking, an increased amount of perlite is necessary because the soil is compact and not light and fluffy. Perlite allows for some oxygen to remain in the soil which helps the roots to grow, and it also allows the soil to drain. Another non-negotiable ingredient that is vital to maintaining soil block integrity is peat moss or the alternative coconut coir. Peat moss and coconut coir are very fibrous and hold the soil block together so that it can withstand many waterings before the root system is fully established. One thing worth mentioning is that peat moss has questionable sustainability in comparison to coconut coir. Peat moss is a moisture-absorbing plant residue found in bogs and swamps that takes hundreds of years to mature. Coconut coir is a byproduct of the food industry in Southwest Asia, and using it in the garden essentially helps to reduce plant waste in landfills. We ended up purchasing one bale of peat moss because by the time that I decided on a soil block mix recipe, it was too late to order the coconut coir in time for us to start doing trial blocking runs. Our bale of peat moss is pretty large so I think that it will last us at least a few seasons worth of soil blocking, but after we use it all we will transition to coconut coir as a more sustainable product for our future soil blocking mixtures.
Although I’ve been doing trial soil blocking runs for the past few weeks, I finally made three full trays of soil blocks last weekend and kicked off the 2021 gardening season by starting our tomato, pepper, and pea seeds. I decided to measure out the ingredients for our soil blocking mix in “parts”, with my “part” being a large wonton soup container. I mixed 50/50 equal parts organic potting soil and peat moss into a large bucket and also added additional perlite until it just looked “right” – which is kind of a funny thing to say since I have no idea what I’m doing when it comes to concocting a soil blocking mix. Once most of the bucket was full of dry materials, it was time to add the water. Thankfully, in my final soil blocking research I came across a blog post that suggested using warm water. Not only did the warm water allow the soil blocks to start off warm for the little seeds, but it saved my hands. It was cold and windy on the day the blocks were made, and making the blocks would have been impossible had I not read the warm water tip. I added more and more water and mixed the dry ingredients until they were fully saturated. Peat moss is highly absorbent and must be dampened and mixed thoroughly, so you will definitely use more water than you think. Many websites suggested letting the wet soil blocking mixture sit for a few hours before using it to make blocks, but I only waited about 10 minutes and everything turned out just fine.
Once the mix is ready, it’s time to start blocking! I have to give a big shout out to my mom who helped me navigate my first round of soil blocking while Doug and my dad worked on constructing our new chick brooder and chicken tractor. I wasn’t lying when I said that my parents are such an integral part of our farm! My mom and I used the fish cleaning station as our soil blocking work station because it is a high work area that allowed us to stand up while working comfortably. We each dumped a bunch of soil blocking mix into plastic trays and away we went.
How to Make a Soil Block
To make a soil block, push the soil blocker down into the container of soil block mix until it hits the bottom, then rock back and forth to ensure that the soil is firmly packed into the blocks. You should see water coming out of the top and out from around the soil blocker as the soil gets squished inside. Once each section of the blocker is full, we used our hands to compress and pack the soil mix into each part of the blocker. The more compact the blocks are, the sturdier the structure will be. We also used our hands to level out the soil at the bottom of the soil blocker. This ensured that each block had an even base and would sit in the tray evenly. This is a very important step because if any of the blocks are uneven on the bottom, they won’t sit flat in the tray and they won’t absorb water correctly. To eject the soil blocks from the blocker, lift the blocker into the block tray and push the spring loaded handle to release the soil blocks. Do a happy dance or squeal a little bit because you just produced your first soil blocks!
We kept an additional bucket of warm water nearby to rinse the soil blockers in between each batch of blocks. I can attest that this is also a very important step – we found that if we didn’t rinse the blocker in between each batch, the corners of the subsequent blocks would get stuck in the blocker and the blocks would be slightly deformed. Rinsing between each batch is super quick and worth it.
Once the soil blocks are made, seeds are started like normal. Depending on the size of the seed, you can sow 1-2 seeds per soil block. When sowing the seed, do not press it into the block as this may cause the block to break. Instead, drop the seed into the indentation and gently sprinkle some soil block mix over the seed. Many soil blocking resources say that seeds in soil blocks don’t need to be covered with soil and will germinate uncovered in the blocks, but we were already out of our comfort zone with the blocking in general, so every seed got lightly covered with some dampened soil blocking mix. Purely because it made me feel better. We sowed one pea seed per block and two tomato and pepper seeds per block. If both seeds germinate in the pepper and tomato blocks, the weaker seedling will need to be cut at the soil level soon after germination.
Soil blocks must be bottom watered because overhead watering may cause the blocks to crumble and seedlings may get dislodged. Once seedlings have germinated, light overhead watering with a fine mist sprayer may be done to prevent the top of the blocks from drying out. Using shallow trays with rims and completely solid bottoms will allow the blocks to be watered from the bottom. The soil block will absorb water from the bottom of the block and bring it to the top through capillary action. As the block absorbs water, the color of the soil changes from light to dark as the water rises – pretty cool! Be cautious of the amount of water that is added to the bottom of the soil block tray and do not allow the blocks to sit in water because this can lead to root rot and mold. Brand new soil blocks contain a large amount of water to begin with and should be checked every few days. New seedlings will require little water and supplemental water can be added as needed. Once seedlings grow larger and have a bigger root system, more frequent watering will be necessary (watering info from Journey with Jill). We use heat mats to help our seedlings germinate, and during our soil blocking trials we found that blocks that were in the solid bottom plastic watering trays did not get as warm as the blocks that were in trays that have holes in the bottom. Because of this, we decided to put all of our soil blocks in trays with holes in the bottom so that they can get as warm as possible on the mats. When it is time to water them, we pour about an inch of water into the solid bottom watering tray and we gently lower the tray of soil blocks into the watering tray. The holes in the bottom of the soil block trays are big enough that the soil blocks absorb the water through the holes. Once the soil blocks are visibly re-saturated, we take the tray of blocks back out of the watering tray and carefully put it back on the heat mat. We are only a week into the process but this seems to be working really well for us.
So far, after a week of being started, every single pea seed has germinated. None of the tomatoes or peppers have germinated yet, but we won’t expect to see them for another week or longer. We also had our first soil block casualty earlier in the week, which is probably (definitely) my fault. Throughout the past month during my soil blocking experimentation, my feline greenhouse companion Marmie kept me company and also tested the heat mats for quality assurance by napping on them. Which I obviously thought was really adorable. Well, one day this past week while I was inspecting the blocks, Marmie jumped directly into the tray of peppers and miraculously only destroyed eight of the blocks. I’m sure the neighbors could hear me screaming, and suddenly Marmie lying on the heat mats wasn’t as adorable as I once thought. I ended up carefully removing the messed up blocks from the tray, making new blocks, and restarting the respective seeds for each block. Lesson learned. Otherwise, everything seems to be going as planned. We will be making our next round of soil blocks in a week or two so we can start our eggplant, okra, and bean seeds. I’m still worried that our soil blocks won’t work out and that our garden will suck this year, but I’m also trying to have faith in the process. They don’t say that to plant a garden is to believe in tomorrow for nothing, right?