Soil blocking is simple, neat, and gaining popularity. Many a gardener say it works well and helps grow strong plants from the start. The best part is, there is no mess, less waste, and roots grow better. Sounds too good to be true, doesn’t it?
In this guide you will learn what soil blocking is, how to do it at home and why it’s better than other seed-starting methods.
But first, let’s answer the obvious question…
Table of Contents
What is the soil blocking method?
This is a technique that allows you to start seeding in an eco-friendly way. All you need is a tool called a soil blocker, also known as a soil block maker. With it, you press soil into little solid blocks. Each block holds a seed right in the middle that acts like its own tiny pot. When you get used to this method, you will no longer have to buy any plastic containers.
Now let’s discuss some pros and cons…
Advantages
- On the plus side, soil blocking cuts out the need for plastic pots and trays. That means less waste, fewer trips to the garden centre, and more money saved over time.
- It also helps roots grow better. In a regular pot, roots tend to circle and tangle. In a soil block, they hit the air at the edge and naturally stop growing in that direction. This process is called air pruning. This encourages the plant to grow stronger, healthier roots.
- Transplanting is easier, too. Since there’s no pot to remove, you disturb the roots less, which reduces shock and helps the plant settle faster.
- Soil blocks are also space-saving. They sit close together on a tray, which is handy if you’re short on room. Plus, they drain well, so you don’t end up with soggy, waterlogged soil. If your plants were healthy, you can even reuse the old soil by mixing in fresh compost and rewetting it.
Disadvantages
There are a few downsides you need to know about, as well.
- There’s a bit of a learning curve. Regular compost is too loose; you need a mix that holds shape. Getting the soil mix just right so the blocks hold their shape can take a few tries.
- Because the blocks are small and fully exposed, they can dry out faster than pots. You’ll need to keep an eye on moisture levels.
- You need to be familiar with the different sizes of soil block makers on the market, depending on what you want to grow. The standard size makes blocks about 5 cm across, perfect for most vegetables and flowers. Mini blockers make very small blocks, roughly 2 cm wide, and they’re great for starting tiny seeds like lettuce or basil. Then there are larger soil block makers, 7 to 10 cm wide, which work well for bigger seedlings that need more room or to stay inside longer before transplanting.
Benefits of soil blocking in gardening
- Environmental impact – Soil blocking cuts out plastic, as you already learned. That means less rubbish goes to the landfill and less plastic bought in the first place;
- Cost efficiency – Once you’ve got your soil blocker tool, you don’t need to buy any more pots. You can mix your own seed-starting mix too, which works out cheaper than what you usually buy in bags;
- Space-saving – Soil blocks are neat and small. You can fit loads onto one tray without crowding. This is great if you’re short on room, like growing on a windowsill or in a small greenhouse.
- Improved soil drainage – Because soil blocks are free-standing, extra water drains away easily. This helps keep the blocks at just the right moisture level and stops seedlings from sitting in soggy soil;
- Better transplanting success – Since there’s no pot to take off, you don’t disturb the roots much when you plant the seedling out. Less stress for the plant means it settles quicker and keeps growing well.
Soil blocking is also a smart first step for anyone planning to start container gardening. The seedlings you will get for your containers will be stronger and less stressed.
Step-by-step guide on how to make soil blocks
Soil blocking looks tricky at first, but once you get into it, it’s pretty easy. Let’s start with…
Needed materials
- Soil blocker tool – You can buy one online or at garden shops. It’s best to start with the standard 5 cm size;
- Seed-starting mix – Fine texture is best, but you can also buy a mix or make your own;
Water – A jug or spray bottle works well; - Tray – The best trays for soil blocking are flat, waterproof, and with no drainage holes. If you have an old baking tray or seed tray, then you’re good to go;
- Seeds – Whatever you fancy growing.
DIY soil blocking process
Let’s start with the soil blocking mix recipe.
Step 1: Prepare the soil mix
- Start with a large tub or bucket for mixing;
- Add the following ingredients:
- parts peat moss or coco coir to help retain moisture;
- part compost or well-rotted manure for nutrients;
- 1 part vermiculite or perlite to keep the mix light and well-drained;
- (Optional) A small amount of garden soil or worm castings for extra nutrients.
- Mix the dry ingredients thoroughly;
- Slowly add water while mixing.
Check the texture often. You need a mix that holds water but still drains. It should feel damp, like a wrung-out sponge and not dry and definitely not soggy. If it’s too wet, the blocks will fall apart. Too dry, on the other hand, and they won’t hold shape. Take a piece and squeeze it. If it doesn’t crumble or drip, it’s ready to use.
Step 2: Fill the soil block maker
Press the blocker down into the mix, and twist slightly as you go. Pack it in tight so there are no gaps.
Scrape off any extra soil from the bottom. Press the blocker again into the pile if it’s still not full. You want firm, even blocks.
Step 3: Making the soil blocks
Now press the blocker firmly onto your tray. Hold for a second, then lift it straight up. You should see clean blocks sitting side by side.
You might encounter these two common problems when you first start out. The first one is, the mix is falling apart. That’s because it’s either too dry or not packed enough. The second one is wonky blocks. The tray might not be flat, or the mix might be lumpy. Don’t worry, just try again. You’ll get the feel for it.
Step 4: Planting your seeds
Each block has a small dent on top, that’s where the seed goes. How many seeds per soil block? You can put one or two per block. Some people do this to be safe and thin out the weaker one later. Gently press the seed into the hole and sprinkle a little soil or vermiculite on top.
Step 5: Watering and caring for the growing plants
Use a spray bottle to gently mist the blocks. This works well right after you have planted the seeds, when they’re delicate. Later on, pour a bit of water into the tray so the blocks soak it up from below. After about 10–15 minutes, pour out any water that’s still sitting there. Keep the blocks moist but not soaked. This is how you bottom water soil blocks.
Put them in a warm, light spot like a sunny windowsill or under grow lights. Aim for steady warmth of about 18–22°C. If germination is slow, then it could be too cold or too wet. Once seedlings have their first true leaves, use a weak liquid feed every week or two.
Step 6: Transplanting the seedlings into the garden
You know it’s time to move the seed out when:
- Roots reach the edge of the block;
- The plant has two or more sets of true leaves;
- The weather is mild (if you plan to plant outside)
Lift each block gently with a spoon or your hand. Don’t squash the roots. Dig a small hole and put the block straight in. No need to break it up. If you’re not sure if it’s time yet or not, make yourself familiar with a gardening calendar.
Also, watch for pests like aphids, sudden cold snaps or overwatering once outside.
You can reuse old soil from blocks if the plants were healthy. Break it up, mix in fresh compost, and re-wet it before making new blocks.
Is your garden slightly out of control? Be honest, now. Schedule your garden maintenance today!
Enter your postcode to view our rates and availability in your area.
For questions about the services we offer visit our main site or you can always call us at 020 3404 4881
Does the soil blocking method work for all kinds of plants?
Soil blocking works well for loads of plants, but not all of them. Here’s a quick look at what actually grows well in soil blocks:
- Tomatoes – They do great in blocks. In fact, soil blocking tomatoes is a common choice for many gardeners;
- Peppers and chillies – Also a good fit;
- Lettuce and leafy greens – Germinate fast and transplant easy;
- Herbs – You can grow your own herbs like Basil, Parsley, Cilantro and Chives.
Can you start squash in soil blocks? Yes, you can. But start them later in the season. Squash grows fast and doesn’t like to sit around in blocks for too long. Use bigger blocks (around 7–10 cm) so the roots have more room. Transplant before the roots outgrow the block.
Can I start carrots in soil blocks? Not the best idea. Carrots hate being moved. They grow a long taproot that doesn’t like being disturbed. You’ll get bent or stunted carrots, so best to sow carrots directly in the ground.
Other plants to avoid in blocks are parsnips, beets (can work, but better direct-sown), radishes and turnips.
Can I try soil blocking indoors?
Yes, you can use soil blocking indoors. It works well in small spaces like a windowsill, spare room, or even a shelf in the laundry. You don’t need much either. Just a tray, some light, and a bit of care. You already know how to make your own block in a tray, so that’s covered.
Do not underestimate the importance of light. Without enough light, seedlings grow weak. If your window gets a lot of sun, great. If not, you might need a small grow light.
Then comes the issue of warmth. Keep the room warm; around 18–22°C is good for most seeds. If the room is cold, a heat mat under the tray can help them sprout faster.
Also, watch for mould or fungus. You don’t need a big fan just open a window now and then, or leave a door open. A bit of air flow helps tremendously.
Takeaways
- With solid blocking, the soil is the container;
- Roots grow stronger and healthier when not in a pot because of the so-called air pruning;
- Soil blocking is space-efficient as blocks sit close together on a tray;
- With a soil blocker, you’ll use fewer supplies over time and produce less rubbish;
- It works on many plants like tomatoes, herbs, lettuce, and brassicas;
- Works great indoors with the right light, warmth, and airflow.
