Do you remember when you were a kid and all you had to worry about was who was going to share your little trowel and little bucket with in the sand pit? Making mud pies and sand castles and those mud blob towers at the beach? Remember how nice that was?

Well, I love to tell you that soil blocking is kind of the adult version of all that – well, at least for me!

Soilblocks are a mix of soil/compost and water, you can add things like coco coir, perlite and vermiculite for added drainage and water retention properties. There are several recipes out there on how to make the perfect mix and I’m still working on mine (first year for me using perlite and vermiculite). However you can just use multi purpose compost. I’ve done that ever since having them (got the Lilac Gift Set from my husband for my birthday in 2023), but I do find the micro ones dry out quicker and the mini 4 ones go so solid that even once you have the season finished and pull up a plant the block is still there with all the roots poking out 😆 So working in other materials may very well be the better option – what do I know 🤷‍♀️

Lets get into it! Welcome to the wonderful world of Soilblocking

So what are they then?

Just as it says on the tin, a little block of soil. A soil blocker (comes in various sizes) creates a little block of soil with an indentation for a seed. Creating a space that retain moisture and it’s shape for a seed to sprout and a seedling to grow strong roots. One of the benefits of soilblocks is that they are square. This shape, compared to a round pot, prevents a plant going root bound. A circular pot will allow roots to go round and round because there is no resistance. This is also why you should always dig a square hole for plants you’re planting in the ground.

A square hole, or soil block in this case, means that when the roots reach the sharp corners of the square, they are more likely to spread out horizontally into the surrounding soil instead of circling around in a confined space at the edge of a round hole, leading to a stronger, more established root system; essentially, the square shape encourages roots to break through and explore the native soil more readily. With soilblocks there’s minimal space compared to the outside of course meaning that roots will grow out of the soilblock, which is completely safe. Not having to fight against sides of a container you also reduce the risk of transplant shock, this in turn makes for healthier and sturdier seedlings and plants!

There are several sizes of soilblockers and various inserts to accommodate different seed sizes. Below are the two that I have:

• The Micro 20, this is the smallest soilblock maker creating 20x 2x2x2cm little cubes ideal for the teeny tiny dust like seeds up to things a little bigger like celery and aubergine seeds or even chili & tomato.
• The Mini 4, this one is the next size up making 4x 5x5x5cm soilblocks and the most versatile one. It can have three different types of inserts; Seed pin, Dowel pin and Cube. Now the Cube insert is the size of the Micro 20, this means that “potting on” (“blocking on”?) becomes a breeze as you simply drop the micro cube into the mini cube and you’re done! the roots will continue to grow through the mini and voila, success.

Soilblockers come in a variety of sizes that I do not have, there’s a Mini 5 (sadly the Micro 20 cubes won’t fit into that one), the Maxi 1 that can have the Mini 4 slot into it and many, many others.

The end goal is to create a wet enough mix that holds its shape, to not fall apart because it’s too dry or too wet, practise makes for better practise and it might take you a few goes to get the right consistency. Remember to play!

User instructions*

• Wet your mix thoroughly in a mixing tub until it takes on a soft putty consistency. You can test this to grab a handful, squeeze out any excess water to see if the blob you just created holds it wonderfully wonky shape.
• Press your soil blocker firmly into the mix a few times to fill the squares.
• I personally like to push it in a bit further with my fingers to really get the mix in there and around the various inserts. Add more mix to make sure the block is firm & full enough to hold.
• Scrape your blocker to remove any excess compost mix from the bottom of the blocks, this helps the blocks to sit flat on your trays. You can use the edge of a tray or just your hands.
• Place your blocker on a flat surface, ideally where the blocks need to go. Press the soil blocker plunger to eject your blocks into your chosen tray. Repeat until your tray is full or you have the amount of blocks needed.
• Each block, Micro 20 or Mini 4, will have an indentation to have a seed on, use a toothpick to slightly cover any seeds if they need to be under a tiny bit of soil or if the seed is so small you can’t hold it with your fingers. If using the Seed insert or Dowel insert for larger seeds, either fill the hole in with more mix or use a toothpick to fill the hole in.

No watering is needed for the first 2-3 days, after that the blocks are best watered with a spray bottle and mist the surface, or bottom water using a small watering can or a fine spray from a hose. make sure to not disturb the integrity of the blocks.

*adapted instructions from the Soilblocker’s manufacture leaflet that I got with my set to how I tend to use it.

It’s fairly straight forward, simply mixing a variety of soil, compost, drainage and water retention aids like perlite and coco-coir and you’re good to go. You can find various “recipes” online including from the soilblock creators themselves. I’m on my third different way of mixes.

• The simplest so far of Multi purpose peat free Compost and water
• Another easy one is Multi purpose peat free Compost, coco-coir  and water (I used more compost to coir ratio)
• The most ‘complicated’ one so far is Seedling peat free compost, coco-coir, vermiculite, perlite and water (pictured). I’m still working through the ratios and whilst photographing this mud fest I added way too much water making the cubes break apart easier. Easily solved by adding more compost etc.

It’s all trial and error and I’m a strong believer of do what works for you and especially your budget. I also want to add that this year is my very first time using both perlite and vermiculite and am yet not 100% convinced yet on their effectiveness. Time shall tell. So far though, I think I prefer the just soil version.

Fore those interested, I’ve bought the following for my mix this year:

Gro-Sure Perlite*
This naturally occurring volcanic rock has been heated to high temperatures to produce lightweight, micro-porous granules. This is perfect for improving aeration, moisture retention and drainage.

Gro-Sure Vermiculite*
Gro-Sure vermiculite is a naturally occurring non-toxic mineral heated to high temperatures to produce lightweight highly absorbent flakes. Retaining both water and nutrients, it releases them as required to encourage faster seed germination and establishment.

Coco-coir*
A by-product of the coconut industry, it is sustainably sourced and more environmentally friendly than peat moss. Better still, it’s pH neutral, with excellent water retention and superb drainage. Just a small block can create 10L, just add water and watch it expand. It does not contain any nutrients plants need so do mix this is with things that do. It is great for seed starting as the first things seeds need are warmth and light.

*info taken from the packaging

Soilblocks on their own are great but not having a tray under them makes watering a little tricky. You can use various trays for this:

• For seed starting I like using takeaway/ready meal tubs for the micro and mini sizes. I find that using a sharpy to write on the lids and tubs themselves bypasses the need for any labels and the writing easily washes off with warm soapy water and a scrubbing sponge. I can get 40 micro blocks or 6 mini blocks in one tub. Making it easy to sow teeny tiny seeds.
• For the next phase I like using these ‘shoe’ trays from Ikea. They’re inexpensive and will last probably forever (yes, more plastic sadly, but, you can use other things you already have, even build something out of wood or even metal – as long as it is water tight). The trays can hold up to 65 mini cubes with ease.
• For the next size up from the mini blocks I like using these cell trays I got in bulk from a potato farm a good few years ago. The cells are a bit larger – in both depth and width – than the mini block and I usually plant out from this stage onwards. Each tray has 15 cells and 3 of those will fit on 1 ‘shoe’ tray
• Another tool I like using are these racks which are also from Ikea and fit in the ‘shoe’ tray so you can stack if space is limited. I use this for both seed sowing indoors (now with my heatmats and growlight) as well as later stages in the greenhouse and even outside with hardening off – if I remember to do so.

So there we go, Soilblock 1-0-1 – sort of, I by no means will claim that I’m a pro at using these, merely that I love using them and this is how I use them to the best of my knowledge. I hope you got excited about them as much as I am and perhaps give a plastic free alternative to seed sowing and potting on a go!

 

*all products linked are ones I’ve bought myself. None of this is affiliated or sponsored in any way