Learn how to start soil blocking for seed starting this spring. Soil blocking is a great way to start your seeds with almost no plastic pots to store. All you need is something to hold the soil blocks, the soil block maker, and seed starting soil mixture.
When I first started my seed starting set up, soil blocking was still new to me. I didn’t want to change too many things at one time, so I decided to try soil blocking the following year. Honestly, I don’t think I will go back to plastic cells for most of my seed starting.
Soil blocking is so easy, quick and feels like you are playing on the beach, building a sand castle! But in this case it’s blocks!
What is Soil Blocking?
Soil blocking is a method of starting seeds where you create compact, cube-shaped blocks of moistened soil mix to use instead of traditional plastic pots or seed trays. You use a special tool called a soil block maker to press the soil into these small, dense blocks. Each block serves as a mini container for your seed, providing it a place to germinate and grow its initial roots. This method is eco-friendly, reducing the need for plastic, and it’s known for producing healthy, robust seedlings with minimal root disturbance when you transplant them.
Advantages of Soil Blocking
Reduces Plastic Use: One of the biggest benefits of switching to soil blocking is the reduction of plastic waste. Since soil blocks eliminate the need for traditional plastic pots and trays, they are an eco-friendly choice!
Enhances Root Health: Soil blocks encourage healthier root systems through a process known as “air pruning.” When roots reach the edge of a soil block, they are exposed to air, which naturally prunes them. This prevents the roots from becoming pot-bound and promotes the growth of a stronger root system, resulting in healthier plants!
Easy Transplanting: Transplanting seedlings from soil blocks is stress-free for both the plant and you! There’s no need to remove pots or untangle roots, which reduces transplant shock and root damage.
Saves Space: Soil blocks can be placed close together on a tray, providing more space for seedlings under grow lights or in your greenhouse.
Moisture Control: Soil blocks can help maintain consistent moisture levels around the roots. The open-air sides of the blocks encourage excess water to evaporate, reducing the risk of overwatering. This can also lead to them drying quickly, so monitor their moisture daily and spritz with a spray bottle to moisten.
Reduced Disease Risk: The air gap between each soil block can help reduce the spread of diseases that thrive in moist, crowded conditions.
Materials Needed For Soil Blocking
- Soil Block Maker: Soil blockers come in various sizes, so you can choose based on the size of the seeds you’re planting and the seedlings you want to grow. You can purchase a small soil blocker for mini blocks perfect for smaller seeds, all the way to a larger blocker that produces 2-inch blocks for larger seeds.
- Seed Starting Mix: A fine-textured, nutrient-rich soil mix is important for soil blocking. It should be moist enough to hold together but not so wet that it’s soggy. Some gardeners make their own mix including peat moss, coconut coir, compost, perlite, and vermiculite.
- Seeds: Consider the size of the seeds when choosing the size of your soil block maker.
- Plastic Trays or Containers: Although the soil blocks are self-contained, you’ll need something to hold them. Any flat seedling tray or container will do, as long as it doesn’t have drainage holes. You can use items such as a cafeteria tray or cookie sheet will work.
- Watering Can or Mist Bottle: Gentle watering is key, especially right after seeding. A misting bottle or a watering can with a fine rose attachment works well to keep the blocks moist without disturbing them.
- Labels: It’s easy to forget what you’ve planted where, so don’t forget to label your soil blocks with the plant type and sowing date.
How to Make Soil Blocks
1. Prepare Soil Mix
Mix Ingredients: Combine your soil ingredients. A typical mix might include peat moss or coconut coir, compost, perlite, and vermiculite. Aim for a texture that’s fine and crumbly, with enough organic matter to hold moisture and nutrients.
Moisten the Mix: Slowly add warm water to your soil mix until it reaches a consistency similar to a wrung-out sponge. It should have enough water that it holds together when squeezed but not drip water.
2. Fill the Soil Block Maker
Dip into Water: Briefly submerge the bottom of your soil block maker in water to prevent soil from sticking.
Pack with Soil: Make you the soil is 2x as deep as the soil blocker. This will ensure best results when packing the soil blocker. Press down firmly into the soil and scrape off any excess soil to ensure the blocks are compact.
3. Press Out the Blocks
Find a Flat Surface: Choose a tray or flat surface where you’ll press out the blocks. If using a tray, ensure it doesn’t have drainage holes to prevent the blocks from falling apart.
Release the Blocks: Position the soil block maker on your surface, then press down on the handle or plunger. This will releases the blocks from the maker, leaving them intact on the tray.
4. Sow Your Seeds
Place the Seed: Drop 1-2 seeds into each indentation.
Cover Lightly: Sprinkle a thin layer of soil over the seeds if needed. Cover with a humidity dome under grow lights if needed. Place the tray on top of a seedling heat mat for bottome heat which can result in better germination.
Caring For Seedlings In Soil Blocks
Watering
Keep Moist: Soil blocks should be kept moist, but not waterlogged. The top of the block will dry out faster than the bottom, so it’s important to check moisture levels daily!
Use a Mist or Bottom Watering: A misting bottle is an easy way for gently watering young seedlings without disturbing them. As the plants grow, you can start bottom watering by adding water to the tray, allowing the blocks to absorb moisture from the bottom up.
Lighting
Provide Good Lighting: Seedlings need a lot of light to grow strong and avoid becoming leggy. Place them near a bright window or under grow lights for 14-16 hours a day.
Adjust Light Height: If you are using grow lights, keep them just a few inches above the seedlings and raise the lights as the seedlings grow.
Temperature
Maintain Ideal Temperatures: Seedlings generally thrive in temperatures between 65-75°F (18-24°C). Avoid placing them in drafty areas or directly on cold surfaces.
Use a Heat Mat: For extra warmth, especially for warmth-loving plants, I suggest using a heat mat. As soon as the seedlings start to sprout, remove the heat to avoid reaching.
Fertilizing
Start Feeding: Once seedlings have their first true leaves, you can begin to lightly fertilize. Use a half-strength liquid fertilizer every couple of weeks to provide essential nutrients. I swear by this fish emulsion fertilizer. It works on seeds of all types including flowers, fruits, and vegetables.
Thinning
Thin if Necessary: If you’ve sown multiple seeds per block and more than one has germinated, thin the seedlings to leave the strongest one. This reduces competition and ensures healthy growth. Instead of pulling the seedlings out, gently cut the seedlings close to the soil line.
Transplanting Soil Block Seedlings
Wait for True Leaves: Your seedlings are ready to be transplanted into the garden or larger pots when they have several true leaves and have outgrown the soil block, usually in a few weeks, and after your last frost date.
Harden Off: Gradually acclimate seedlings to outdoor conditions by placing them outside in a sheltered spot for a few hours each day, gradually increasing the time over a week before transplanting.