If you enjoy growing your own vegetables and flowers, but are tired of accumulating plastic trays and pots everywhere, the soil blocking method It will sound like heavenly music to you. It's a simple, inexpensive, and very environmentally friendly technique that allows you to produce strong and healthy seedlings…without using a single plastic pot or polystyrene seed tray.
With soil blocking, you transform a special substrate into small, compact blocks where each seed has its own "mini garden." These soil blocks maintain their shape without the need for a rigid container and can be transplanted into the ground or their final pot without stressing the plant. Throughout this article, you will see What exactly is soil blocking, what advantages does it have, what mixture to use, how to do it step by step, and what mistakes to avoid so that your first tests turn out great.
What is soil blocking and why is it so trendy?
Soil blocking (or “substrate blocks”) is a plant propagation technique in which seeds are sown in self-supporting earth blocksThat is, cubes of compressed substrate that don't need pots or seedling trays. The block acts as both container and growing medium.
To create these blocks, a manual tool is used, called soil blockerThis process compacts a very moist substrate mixture into firm cubes. Each cube has one or more small holes where the seeds are placed. Once sown, the blocks are arranged very close together on a flat tray, making the most of the available space.
This system is especially popular among organic gardeners, artisan nurseries, and hobbyists who want reduce plastic use, improve root quality and save space in greenhouses and grow tablesAlthough it may seem like something modern, it derives from traditional horticultural techniques that were widespread before the invasion of cheap plastic pots.
Advantages of soil blocking versus plastic pots
The main appeal of soil blocking is that it offers a combination of sustainability, savings and more robust plantsdifficult to match with conventional seedbeds. These are its most important advantages.
1. Much more environmentally friendly and with less waste
By eliminating the need for seed trays and pots, soil blocking minimizes plastic consumption. There's no need to buy new trays every season or dispose of broken or warped containers. You only need one or two durable metal tools and a few flat trays that you can reuse indefinitely.
In this way, your seedbed generates very little waste and your garden becomes more consistent with a philosophy of sustainable farmingIf you also choose substrates with low environmental impact (homemade compost, coconut fiber, vermicompost, etc.), the whole system is much more environmentally friendly than methods based on disposable plastics.
2. Healthier roots and stronger seedlings
In a plastic pot, the roots hit the walls and start to spin in circles, causing the classic root curling which ends up affecting the plant's development. In substrate blocks, the opposite occurs: when the roots reach the edge, they encounter air, dry out slightly, and the plant sends out new roots towards the interior of the block, instead of continuing to grow in circles.
This phenomenon, known as air pruning or aerial pruningThis results in a compact, branched root system ready to explore the soil as soon as it is transplanted. The result is usually rapid establishment, less growth retardation after transplanting, and better water and nutrient uptake in the first few days.
3. Less transplant stress
With soil blocking, you don't have to remove the plant from its pot or squeeze the root ball to get it out. It's simply transplanted. the entire block into the planting hole, without breaking roots or crumbling the substrate. The plant barely notices the change, because it maintains its root structure intact and the beneficial fungal mycelium remains attached to the block.
This method of transplanting significantly reduces the water and mechanical stress that seedlings suffer. You will see that seedlings sown in blocks recover better after being moved to the garden, show fewer limp leaves and resume growth in less time than those grown in rigid cells.
4. Space saving and flexibility
Soil blocking blocks can be placed very close together on flat traysWithout walls to take up space, this means you can grow many more plants in the same area as with traditional cell trays. Furthermore, if you need to move or rearrange some blocks (for example, to separate varieties that germinate earlier), simply slide them out or transfer them to another tray.
This density also simplifies irrigation in the initial stages, as all blocks receive the same humidity from below If trays with a water layer or capillary action are used, the absence of individual walls makes it easier to manage large quantities of seedlings without dealing with deformed or broken trays.
5. Medium and long-term economic savings
Although the soil blocker tool may seem like a slightly higher initial investment than simple plastic trays, it pays for itself quickly because it is used year after yearIt doesn't break easily and it doesn't warp in the sun. By reducing the constant purchase of new pots and substrate to refill them, the system pays for itself in just a few seasons.
Furthermore, the substrate mixture used for the blocks is usually very efficient in the use of organic matterYou don't need to fill large pots from the start, because each block is the perfect size for the seedling stage. This avoids waste and optimizes resources, especially if you start many seedlings each season.
How the soil blocking tool works
The key component of the system is the substrate blocker or soil blockerIt consists of a metal body with several cubic molds (2, 4, 5, 20 or more, depending on the model) and a mechanism that compacts and ejects the formed blocks. It is pressed onto the moist substrate, the lever or handle is activated, and the cubes appear perfectly compressed, with their small cavity for the seed.
There are several standard sizes of soil blocker, designed for different stages of cultivation and seed sizes. The most common are:
- Microblocks 1-2 cm, designed for very small seeds or to produce a large number of seedlings in a small space.
- Small blocks 3-4 cm, perfect for most garden vegetables (lettuce, cabbage, annual flowers, etc.).
- Medium or large blocks 5-7 cm, suitable for crops that need more time in seedbeds (growing tomatoes, peppers, squash) or for a more advanced transplant.
Some models allow insertion interchangeable pivotsThese are points that leave a deeper or wider gap, or even a square hole where a germinated microblock fits perfectly. This allows you to "scale" the seedling: start in a very small block and, once the root has colonized it, fit it completely inside a larger block to continue growing without stress.
Ideal substrate mix for making stable blocks
For the system to really work, the key is to use a specific substrate mix for soil blockingwith the right texture and moisture content. Garden soil alone won't do: it crumbles, becomes too compacted, or cracks when it dries.
In general, a good recipe combines three types of ingredients: structure, water and nutrient retentionFrom there, each gardener adjusts the formula according to their climate, available materials and type of crop, but the base is usually similar.
Typical components of the mixture
- Very fine mature compostIt is the main source of nutrients and beneficial microorganisms. It must be well sifted, without sticks or stones, so as not to break the cohesion of the block.
- Coconut fiber or blonde peatThey provide lightness and water retention capacity. Coconut fiber is more sustainable and rehydrates easily.
- Fine sand or vermiculiteThey improve drainage and help prevent the block from warping. Vermiculite also retains moisture.
- Garden soil or coarser compost in small proportions, to give some weight and stability, always well sieved.
- Soft amendments (rock flour, very fine wood ash, etc.) in moderate quantities, if additional minerals are desired.
Many homemade formulas use proportions like: one-third fine compost, one-third coconut fiber, and one-third sand or vermiculite, adjusting later depending on how the blocks behave. If you notice that they break with nothingIf they are muddy and very heavy, there is too much water or the substrate is too compact.
The right moisture: the famous “brownie point”
One of the most important tricks for making perfect blocks is to hammer them in. the amount of waterThe mixture should be neither dry nor runny. It's often said that it should have the consistency of a brownie: when you take a handful, it holds together, is moist to the touch, but doesn't drip.
To achieve this, it's best to add water little by little while thoroughly mixing all the substrate, preferably in a large container or wheelbarrow. When you think it's ready, Check by squeezing with your handIf it crumbles when you release it, add more water; if you see puddles or streams when you squeeze it, it's too wet and you should add some more dry mix or let it sit for a few minutes to absorb the moisture.
How to do soil blocking step by step
Although it might seem technical on paper, once you do a few batches you'll see that the process is very simple and almost mechanical. These are the basic steps for form your first substrate blocks no mysteries.
1. Prepare the mixture and the work area
Start by sifting the coarser ingredients (especially the compost and soil) to remove stones, roots, and large pieces. Then mix all the dry ingredients until you achieve a smooth consistency. Next, gradually add water until you reach the desired consistency. wet, dense and workable mixture.
Place the prepared substrate in a deep tray, a wide bucket, or directly in a wheelbarrowNext to it, have a flat tray ready where you will place the formed blocks, and the soil blocker tool clean and slightly moistened, so that the metal substrate does not stick to it at first.
2. Load the soil blocker
Introduce the substrate blocker into the mixture with a pressing and rocking motion, making sure that Each mold fills wellDon't just place it on top: push down, give it a slight twist, and repeat a couple of times if necessary to compact the mixture well inside the cubes.
When you think they're full, run the bottom of the blocker along the edge of the container to remove any excess substrate. This ensures all the blocks come out at the same height and the base is flat, which is key for... don't wobble on the tray.
3. Unmold the blocks onto the tray
Place the soil blocker on the flat tray where you will grow the seedlings. Choose a corner or a side to arrange them in rows, so that so you can make good use of the spaceActivate the lever or ejection mechanism with a firm, vertical motion, without rotating the device, so that the blocks come out straight.
Carefully pull the tool upwards. You should see a series of well-defined cubeswith marked edges and a small hole at the top of each one (if your soil blocker model comes with planting pegs). If any have come out crooked or broken, you can undo them and return the substrate to the pile to try again with more pressure or by adjusting the moisture.
4. Sow the seeds in the blocks
Once you have a row or the entire tray filled with blocks, it's time to sow. Place the appropriate number of seeds in each space, depending on the species: normally one seed per block If they are expensive or medium-sized, and two or three if they are very small or germination is irregular.
Lightly cover the seeds with a little fine substrate or vermiculite, respecting the recommended depth for each crop. There's no need to press down too hard; just make sure that not be completely exposedIf the soil blocker does not leave a gap and the blocks are flat, you can make small depressions with a pencil or the tip of a stick.
5. Initial irrigation and moisture management
After sowing, it's advisable to water gently to settle the seeds and finish compacting the surface. Ideally, use a a very fine mist watering can or a spray bottleto avoid damaging the freshly made blocks. Another option is to place the tray on top of another one with a little water, so that the cubes absorb moisture from below through capillary action.
During the first few days, keep the blocks always slightly damp, never waterloggedIf they dry out completely, they will crack and lose their cohesion; if you overwater them, they can disintegrate or encourage mold growth. The most practical approach is to water them sparingly and frequently, checking with your finger that the inside retains moisture without becoming muddy.
Care of seedlings in soil blocking
Once the seeds germinate, the blocks become small "floors" where the seedlings spend their first weeks. At this stage, it is necessary to closely monitor light, temperature, and irrigation, just as you would with any other seedbed, but with some particularities of the system.
appropriate light and temperature
Place the trays in a place with good indirect lighting or filtered sunlight Depending on the crop. If the plants start to stretch excessively (thin and very long stems), they probably need more light. In that case, move them closer to a brighter window, remove overly opaque protective plastic, or, if you're growing indoors, consider using grow lights.
The ideal temperature will depend on the species, but in general most vegetables appreciate it. a temperate environment For germination (around 18-24°C) and slightly cooler once the first leaves have emerged. If it's too cold, the blocks will take longer to dry and the risk of mold increases.
Watering: neither too little nor too much
Soil blocking blocks have less volume than a large pot, so they dry fasterEspecially if there are drafts or the room is very hot. It's important to check them daily, occasionally lifting a block with your hand to feel its weight: if it's very light, it needs water; if it's quite heavy and looks dark, it still retains moisture.
Capillary irrigation from below, by maintaining a thin layer of water in a lower tray, helps to maintain humidity more stablyJust make sure the water doesn't completely cover the blocks to avoid soaking them. If you prefer to water from above, do so with a fine spray, trying to wet the entire surface evenly.
Fertilization and growth
If the substrate mix was well prepared, seedlings usually don't need additional fertilizer in the first few weeks. However, in long-cycle crops or if the planting blocks are small, nutrients may start to run low. At that point, it's useful to... Apply a mild liquid fertilizer diluted in irrigation water, or use rooting hormones, once every 10-15 days.
Observe the color of the leaves: if they yellow quickly or growth stagnates, it could be a sign of nutrient deficiency. Instead of applying a large amount of fertilizer at once, it's preferable to use low but regular doses, so as not to burn roots or alter the block's structure too much.
When and how to transplant the blocks to their final location
The ideal time for transplanting is when the plant has a well-formed root system but The block has not yet been fully colonizedIt usually coincides with the appearance of 2-4 true leaves (beyond the initial cotyledons) and vigorous development, without symptoms of stress.
To transplant, make a hole in the ground or in a pot slightly larger than the block. Place the cube of substrate inside, making sure that remain at the same depth Plant the seedling in the tray (don't bury the plant's neck too deep, except in crops that allow it, like tomatoes). Fill around it with loose soil and water well to settle.
One of the great advantages of soil blocking is that you don't have to disturb the roots or remove anything from any container. You simply move the complete block, with its entire structureThis reduces root damage and allows the plant to continue growing almost without noticing the change. Within a few days, you should see a new growth spurt.
Common mistakes and how to avoid them
Like any new technique, soil blocking has its learning curve. Many problems are repeated when starting out, and it's helpful to be aware of them. to save yourself time and frustration.
- Blocks that fall apart when removed from the moldThis is usually due to insufficient moisture or a mix that's too loose. Try adding a little more water or increasing the proportion of binding materials, such as coconut fiber or fine compost.
- Deformed or very soft blocksHere the problem is usually the opposite: too much water or a very clayey substrate. Add more aerated components (vermiculite, sand) or reduce the amount of heavy soil.
- Fungi and “damping off” (Stems that strangle and fall over): Overwatering, poor ventilation, or excessively high temperatures contribute to these problems. Reduce humidity, improve air circulation, and prevent continuous waterlogging.
- Very stretched and weak seedlingsIt's almost always a lack of light. Move the seed trays closer to a bright window or provide adequate artificial lighting.
- Roots growing out the sides Too soon: this could be a sign that the block is too small. In that case, you should either transplant it to its final location now, or move the seedling to a larger block by fitting the first one inside the second.
Which crops are best suited to soil blocking
Soil blocking works very well with most seasonal vegetables and flowers, but some groups benefit particularly from this system. Among them are... fast-growing leaves such as lettuces, endives, chard and spinach, which form dense roots in a short time and appreciate a gentle transplant.
They also respond very well families of cabbages and brassicas (cabbage, cauliflower, broccoli, kale, etc.), annual garden flowers (calendulas, zinnias, cosmos, marigolds), and many medium-sized aromatic plants. For crops like tomatoes, peppers, or eggplants, you can start in small blocks and later fit those blocks into larger ones to prolong seedling growth.
In contrast, species that do not tolerate bare-root transplanting well (such as carrots, long radishes, or certain delicate roots) are not the best candidates, unless You'll hit the right moment and transplanting before the main root begins to deform. Even so, many people prefer to continue sowing these species directly in their final location.
With a little practice you will see which varieties in your garden are best suited to the method. adjusting the block size, the time spent in the seedbed and the type of mix to suit the needs of each crop.
Adopting soil blocking in your seedbed is a simple way to Reduce plastics, improve root health, and optimize space Without complicating your life. Once you master the texture of the mix and the ideal moisture level, the process becomes almost automatic and very satisfying: you prepare blocks, sow seeds, water, and transplant with an efficiency difficult to achieve with conventional pots. Few techniques so perfectly combine ecology, savings, and plant vigor in such a simple gesture as pressing moist soil into small cubes, ready to bring your next garden to life.
