Experimental soil block

I've been wanting to try starting seeds in soil blocks. Being me I have been reading and watching lots on this topic.  I plan to make my own soil block maker. If it works great, and I'm happy with the results, maybe I will buy one in the future, but for now it seems easy enough to make, at little to no cost.
The recipe seems to be the most important part.  I don't like using peat for a number of reasons. Coco coir seems better, but still several things I don't like about it.  There's a paper product called pittmoss.  It seems like a good alternative, but I can't get it locally, so it's expensive, and posing some of the same problems as the coco coir.  I was thinking about experimenting with cardboard.  As much as I wish we didn't, we as a family order to much from Amazon. I shred the cardboard and use it for lots of things.  I was thinking if I soaked the shredded cardboard, and once it's soaked through use the paint stirrer that connects to a drill and make a sort of mash that it would be similar to the pittmoss.  
If this works I will mix it with my worm castings, sifted compost and maybe a little seed starting mix.  I will have to play with the amounts to get the right consistency . I may add a little coco coir, because I do have a little.
I'm not sure if this will work??? I will start some seeds in the plastic pots I already have just in case it's a complete failure. I enjoy trying new things, especially if it involves less plastic.
I'm always interested in thoughts, advice, and your experience.  Thanks

How do you shred your cardboard and how fine are you able to shred it? Do you think it would lose too much of it's structure if you partially composted it after shredding as opposed to the water/stir method? I'm interested in what you discover and hope you will update us all.

I've only ever used peat moss for soil blocks. I don't want to sidetrack this thread with another topic, but do you mind sharing why you avoid it?

I could see this working. I think the key will be getting the cardboard broken down pretty fine, like a pulp. If there are big pieces in the mix, they'll probably compromise the structural integrity of the blocks.

I would definitely plan to include some perlite in the mix for aeration. Since the blocking process compresses everything so much, I could imagine a mix of pulp/castings/compost turning into a real brick that stays too sodden if it doesn't have something to lighten it up a bit.

I think playing around with a blend of coir and pulp sounds promising, and you should play around with the ratios in general. You might find you need more or less pulp to compost in comparison to what the peat and coir recipes call for.

Pittmoss looks interesting, thanks for sharing that idea! I hope it becomes more widely available. I'd love to see some additional peat alternatives crop up. Coir seems to be a pretty good product, but a little more competition would be good for everyone.

Blake Dozier wrote:I've only ever used peat moss for soil blocks. I don't want to sidetrack this thread with another topic, but do you mind sharing why you avoid it?

I'm not sure what the other issues might be, but the most common complaint against peat moss is that it's a non-renewable resource. Mining of peat bogs is environmentally destructive (and if I recall, might also be a significant carbon emitter). It's the kind of thing that we need to eventually stop doing, so gardeners are starting to experiment with ways to get the same results with other materials. Coco coir is popular and has some good upsides. I've been soil blocking with coir for 3 years now and have been very happy with my results.

Blake I use a 15 sheet paper shredder to shred the cardboard. It's pretty small, but I don't think it's small enough that's why I think I should wet and basically blend it up. I will take some pictures and post them as I got.
Ian is mostly right. I have read a lot of negative effects to the environment mining the peat bogs.  Even if it isn't true it isn't local so must waist a lot of resources to get to me. On top of that I live in a hot dry place. In the past I used peat pots. The seedlings never did very well. I dug them up and discovered the peat didn't brake down at all. So I'm not to sure about adding it to the soil blocks.  The coco coir is a similar problem. It's great to use something that would otherwise be a waist product. I have heard there are issues in the labor used to obtain it.  It also comes from far away so again use a lot of natural resources to get to me. Now I honestly don't have a clue what is true, and what isn't. I just try to use what is local and easy to get.  (I'm in no way great at this, we use Amazon after all, but I figure every step in the right direction is better than not trying at all)
Ian the seed starting mix I use has pearlite in it.  If I decide not to use it, I will add it, or course sand.  Thanks both of you for your input.

Blake I use a 15 sheet paper shredder to shred the cardboard. It's pretty small, but I don't think it's small enough that's why I think I should wet and basically blend it up. I will take some pictures and post them as I got.  

I would love to see some pictures! I'm impressed that your paper shredder will handle cardboard.

This article claims peat is responsible for binding the mixture together and retaining moisture (and is the recipe I've used in the past):
https://extension.psu.edu/programs/master-gardener/counties/susquehanna/penn-state-master-gardener-articles/making-soil-blocks

I would think cardboard would have those properties, provided you could get it small enough to homogenate and not interfere with the delicate emerging roots. What would happen if you pushed shredded wet cardboard through a meat grinder? It would probably make a huge mess and ruin something... what about a food processor?

Ian is mostly right. I have read a lot of negative effects to the environment mining the peat bogs.  Even if it isn't true it isn't local so must waist a lot of resources to get to me. On top of that I live in a hot dry place. In the past I used peat pots. The seedlings never did very well. I dug them up and discovered the peat didn't brake down at all. So I'm not to sure about adding it to the soil blocks.  The coco coir is a similar problem. It's great to use something that would otherwise be a waist product. I have heard there are issues in the labor used to obtain it.  It also comes from far away so again use a lot of natural resources to get to me. Now I honestly don't have a clue what is true, and what isn't. I just try to use what is local and easy to get.  (I'm in no way great at this, we use Amazon after all, but I figure every step in the right direction is better than not trying at all)  

I'm not sure what the other issues might be, but the most common complaint against peat moss is that it's a non-renewable resource. Mining of peat bogs is environmentally destructive (and if I recall, might also be a significant carbon emitter). It's the kind of thing that we need to eventually stop doing, so gardeners are starting to experiment with ways to get the same results with other materials. Coco coir is popular and has some good upsides. I've been soil blocking with coir for 3 years now and have been very happy with my results.

Thanks to both of you, Ian and Jen, for your answer. I went through a brief spell where I boycotted Amazon... then drifted back. So I too frequently have a mountain of cardboard. I'd love to eliminate that from my life, but I don't think I'm in a spot yet to totally commit to that. In my opinion, any sort of resuse of a waste product is a step in the right direction. Excited to see the results!

(I have a meat grinder and would be willing to push some cardboard through it as an experiment, so if the paint stirrer doesn't work and you want me to try... let me know)

That's nice of you Blake. I thought of a food processor, but I don't have one. I might be wrong, but seems like cardboard would gum up a meat grinder, and I don't have one of those either.  The blender would probably do the trick with enough water, but I don't know what kind of damage it would do, and it would have to be very small batches.  I know when I soak the shredded cardboard to put in my worm bin it gets very soft. My thinking is soak it for a couple days. Then dump most of the water out, then just stir away. You said the paint stirrer didn't work? I bought this attachment years ago that is for cleaning out pumpkins. It goes into the drill. It's round with sharpish edges. Maybe if I can find it, that will work? I won't know until I try.
Thanks again.

Took a picture of the shredded cardboard. It's not super small. It was the best shredder I could afford at the time.

Thanks for sharing the pic! To be honest, I'm impressed a consumer grade paper shredder does that. I admittedly hadn't ever thought to even try running cardboard through mine.

I think your plan may work! Excited to hear about it!

I found a food processor at the thrift store for $13. Today I gave it a try. I think it's going to work. ???  I was hoping to make some soil blocks today, but I have been lazy and it got to late. I processed some soaked cardboard, made a tray to put the blocks on, and made a sifter to sift the compost and soil.  I decided to buy a small 3/4" seed blocker.  This way I can make 20 tiny soil blocks to start the seeds in. I only have one heat mat. I can start lots of seeds. As seedlings pop out of the soil I will  put them in a larger block. I plan to make a 2" soil block, and maybe a 4" one as well, we will see. I can't wait to give it a try.

Maybe grow luffas as an alternative to coconut coir?

Nikki said, "Possibly as an alternative to coconut coir. I plan to pulverize some and use them in soil blocks to help hold their structure and water retention.

https://permies.com/t/208191/Luffas-ways

Played around with making some soil blocks tonight. It was harder than I thought. I don't think I got the cardboard fine enough.  I'm not sure it's going to work. I ended up putting the mix into the food processor. I had to push the mix into the soil block maker. I don't have my germination station up and going yet so I didn't plant anything yet. I hope I can get seeds planted in a few days. Time will tell if they hold together. I do think I will get some coco coir for the larger blocks, and stick a little closer to the tried and true recipe.

1/20/23 I placed a seed in almost every block. Covered the seeds with vermiculite. I mist everything. Place the tray on the heat mat.
My first worry is the tray I made so the roots would air prune on the bottom, my be to far from the heat mat. For some that won't matter but the tomatoes do better, and almost a must for peppers. Time will tell.

I mist every day. 2 days after I planted dahlia and michihili (Chinese) cabbage have already sprouted. I did soak most of my seeds for about 24 hours. Tiny seeds like tomato don't seem to do well with soaking.  Today is day 4 and I have moved the dahlia, cabbage, and chamomile to a new tray under a grow light. I hope to get my 2" soil block maker made soon. I didn't think I would need it so soon.   I bought some sprouting trays that seem like an inexpensive way to have a preferred bottom, and a solid bottom for bottom watering.
I can see one of the pepper plants starting to grow, so it must be getting enough heat.  

I have already learned several things from this endeavor. First is it's harder than I thought to get the blocks to hold together.  My decision to start with the 3/4" blocks was because I only have 1 heat mat and allowed me to start lots of seeds.

What I like is as the seedlings emerge I can remove them from the heat mat and get them under a grow light. With the cell trays I had to wait until most of the seeds popped up making some leggy.

I wish I would have gotten the larger soil block maker. The 3/4" one is really only good for super small seeds. The larger seeds are sprouting on top of the block without going into the block. I think the dimple in the top of the block is to shallow.  Or the blocks are to compact but some of the blocks already have roots coming out of the bottom, so I don't think that is the case. ???  Anyway next time I will start larger seeds in a larger block.

Everything is sprouting well. It's past time to plant in a larger block. I managed to build a larger block today. I used a piece of wood from a pallet.  I started out using a piece of corrugated steel. I got it cut and bent into shape. I decided it wasn't smooth enough. If it's hard to slide with nothing in it, it probably won't do the job. Plan B. I used a flexible cutting board from the dollar tree. They come in a package of 2. I cut it to shape the corners bend and shape nicely. I meet it at the corner so there's a little overlap on the outside. I duct tape it together. I put a piece of tape on one side with makings every 1/2 inch so I can decide how much soil to fill it with.  I put a 3/4" square dowel 1" long on the end so it will make the hole for the seedling blocks, and a chunk of wood on the other end as a handle.  Will it work??? I hope so. I made it after work, so it's to late and I'm to tired to make my soil so I can try it out. I will make it mostly like the small blocks, but I will add a little coco coir for strength since it will be bigger, and add a little organic fertilizer of some kind.

I've kinda gone off the rails with this post. So I'm going to try to bring it back. The experimental part of this experience. Can you make soil blocks substituting ground up cardboard for peat or coco coir?  I would say yes. It totally works. It formed blocks, held there shape germinated seeds.  I don't know if they are as good as the ones made with peat or coco coir. But if you can't get those, or don't want to buy anything this will work.

The strange thing is the experimental soil blocks made with cardboard as a binder worked very well. The larger soil blocks I use what was left of my first soil mixture and added the more traditional ingredients like peat, and coco coir. I also added some organic fertilizer because I knew now the seedlings will need more.  
The larger blocks are not working very well.  I'm sure it's my mix is off.  I'm just not sure it's worth the effort.  It's been an interesting experience.

Round 2 is a total bust.  I used the unused blocks, from round 1. I've been going over in my head what the difference was. It's the same mix, so that's not it. Not enough water? To much water? Maybe. I strongly suspect it's because I didn't use the 10/20 tray.  The dome is designed to fit the 10/20 tray. It doesn't seal, but fits well and gets a lot of humidity. For the second round I was starting less seeds and put them on a smaller tray. It does get some humidity, but  not like the 10/20 try.  That's my theory anyway.  This weekend I will make some new blocks, put them in the 10/20 tray. See if I can duplicate the amazing results I got the first time.