For those of you that are soil blocking, what mix has worked well for you?
I took the James White module on the GTS website where he talks about the necessity of using native, low nitrogen soil to encourage relationships with nitrogen-contributing endophytes, so I’m interested in hearing what you all are doing that is actually working. The first blocks I did were with a mix of native soil, leaf mold, and woodchip compost, but it didn’t survive my first watering test. So I added some peat moss and vermiculite to the mix and planted them and those blocks are doing okay, but the blocks aren’t staying super defined. This is also my first year soil blocking, so maybe I just don’t know what to do and/or what to expect
I also saw a youtube video of someone comparing three different soil blends for blocking, and the one that included leaf mold resulted in stunting in the seedlings, so now I’m getting nervous that I’ve shot myself in the foot before the growing season has even gotten going!
I soil blocked last year with a mix of bagged compost, bagged seed starting mix, sand, vermiculite, and a bit of sifted native soil. The blocks worked fine but my nutrient balance was off in a bad way (I think the bagged compost had too much incompletely composted wood chip/bark material, leading to severe nitrogen deficit), and the seedlings were badly stunted in an unhelpful way. It impacted species that had a longer time before transplant (I.e. tomatoes, TPS) much worse than things that got transplanted earlier.
This year I’m going to try a much higher proportion of native soil and add sifted leaf mould compost instead.
I’d love to use materials from my garden, but it’s usually frozen solid when I start soil blocking, so I buy ingredients. I make blocks with 4 heaping quarts of rehydrated, fine coir plus 1 quart of worm castings. This amount is good for two 1020 trays. I use warm water to rehydrate the coir, because it’s much more comfortable to handle on a winter day. I add a few tablespoons of all-purpose organic fertilizer. Thoroughly blend ingredients. The mix should be quite wet, otherwise blocks will not stick together. Also important to push the blocker strongly into the mix and be sure the mix is packed into the chambers of the blocker.
If you want to select for nutrient use efficiency in your seedlings, omit the fertilizer. I’d also make many at least 2x soil blocks than you want for planting, since many seedlings may grow poorly in the low nutrient blocks.
We used a lot of soil blocks in the market garden I worked for the last 3 years. We used a mixture of farm soil and a potting compost that was an output of our heat benches. For this, we mixed horse manure with hay in layers and sprayed each layer of hay heavily with diluted lactic acid bacteria (this was essentially intended as a low-tech way of doing bokashi) and then used this mix to heat our seedlings in early Spring. The next year, we sieved this and used it as our potting mix (it’s fairly high nutrient but we never had any issues), combined with some farm soil and ideally some vermicast and some small biochar (or pearlite) for drainage.
There are of course good reasons not to want to use animal manures in your potting mixes, but this worked really well for us both in terms of block consistency and seedling growth. Some things that we found were really important were: sieving the mix properly; getting the right moisture level in the mix (it was higher than I though it would be at first); and dunking the blocker in a bucket of water in between each set - this helped the wet mix come out cleaner.
That’s helpful to hear (especially about the tomatoes/TPS), and it’s definitely a concern I have with my current mix. It’s frustrating that there’s no way to know if I’ve got a problem until… erm.. I’ve got a problem. Perhaps if I find that they’re stunting, I can try a tiny splash of liquid fish when I water. I have to be careful with that, of course… last fall I killed all of my cabbages/broccoli/cauliflower/brussels by being less than judicious in the size of my splash when fertilizing my seedlings
I’ve seen so many people recommend coco coir for soil blocks! Everyone seems happy with it. I don’t have any good places to buy in bulk locally, so I’ve only used peat up until now. If this year ends up a fail, I might have to give it a go.
And yeah, I’m seeding very heavily… hopefully they do struggle a little, otherwise I’m going to be killing off/giving away dozens of plants. I don’t have anywhere near enough room for everything I’m starting!
For Giving Gardens we mix Pro Mix (which has mycorrhizae in it. Happy Frog is another bagged soil mix with a lot of mycorrhizae and nitrogen fixing bacteria) with sifted finished compost and peat moss at about a 1 to 1 to 1 ratio. You have to get it pretty wet ( but not too wet) in order for the soil blocks to hold up well. It takes a bit of practice to get good results. We don’t mix native soil into the soil blocks because the texture isn’t right to produce well formed blocks. Your mileage may vary.
For my personal garden, i direct seed everything… not necessarily to get the best results. I just want plants that can be direct seeded. I don’t want to fuss with starting plants in blocks or containers…
We’re using ProMix mixed with a small amount of compost (either composted chicken manure or Johnson-Su compost, which has a high fungal:bacterial ratio) and it works pretty well. Agree with what others have said about getting the mixture wet enough.
We’ve been using sieved compost from the chicken coop for our soil blocks for a few years now. The coop is filled once or twice a year with a thick layer of fresh wood chips that is then slowly composted by the turning of this mass by the chickens and their manure being added to it. Since we started doing this we have no more ammonia smell in the coop that you have when using thing like straw or wood shavings. Those light materials compact and become nasty fast meaning you have to replace it often. But the wood chips have much more carbon mass to offset the nitrogen in the manure and have less of a tendency to clump together because they’re heavier. The manure and wood chips compost to dark soil like material quite fast keeping the coop much cleaner with often little visible manure around. We also add some other compostables of course to the coop sometimes for the chickens to scratch trough.
We let the chicken compost as we call it rest for a while on a heap before we use it to compost a while more and then sieve it in a rotary sieve that I build for this purpose from salvaged bicycle parts. The compost works great for plants as it contains a good nutrient mix that does not stun them. However it does not contain much fibres like from coconut shells or peat, therefore the soil blocks are more prone to drying out and not rehydrating very fast. To ease watering we thus place them on shallow metal plates that can hold a small layer of water. Runoff water from watering then has the time to soak up from below into the blocks. The blocks are very strong and hold their shape well, but the right amount of water/compost is very important in making them. You’ll get the feel for this quite fast since the blocks either hold up good or not. Wetter mixture will also pop out of the soil blocker more easily. If the mixture is too wet though the soil blocks will be soft and prone to damaging so its best to let them dry for a couple of hours till a day or so before using them.
I’ve also noticed that making blocks with this mixture a long time beforehand and thus causing them to completely dry out is not advisable. Because once the blocks have fully dried out will not only need a long time to soak (they will not dissolve however even if you place them in a bucket of water) but will also have a tendency to form a thin crust on the outside and inside where the seed hole is. Seedlings will then often have a difficult time penetrating this thin crust surrounding the seed hole. So therefore you then have to scrape the seed hole slightly before using those dried blocks. I think if you have a more fibrous mixture this would counteract this behaviour, but since local peat is almost extinct here in the Netherlands and coconut fibres have to be imported from far away I don’t find those things viable options. So we now prefer to just make enough soil blocks to use up within a couple of days (this mostly depends on the weather of course since in hot sunny days the drying in the green house is just much faster).
