Soil Blocks So Far
I've been using soil blocks (vs standard plastic cell trays) for about a year now, I was bit slow (& awkward as always) to get into the swing of it. I've been meaning to write a post about my experience with them for a while now but was kinda waiting till I was a bit more settled in my 'system' so one year on I finally feel for the most part quite happy with how it's all working.
The main reason I decided on using soil blocks were, less use of plastic, better/healthier transplants, ease & efficiency, and having OCD control of what goes into the mix.
Less use of plastic
I make all of my blocks into the webbed mesh soil block trays from Johnny's nested in their leakproof trays. So while I haven't necessarily ended up using 'less' plastic per se, it does feel slightly more efficient when it comes to cleaning & re-using flat trays versus having to clean oh so many little cells.
I do think when I get it right they're great, and don't seem get any transplant shock. I feel like I can get away with starting usual direct-seed-only flowers (orlaya, larkspur etc) in soil-blocks with virtually no root disturbance if planted out before they get too big.
My biggest problems with using soil-blocks (which really would be universal to any system and not the soil-block's fault at all) is I'm terrible at planting them out on time, my bed prep is often a month behind where I need it to be and they get too big and eventually start growing into each other and I kinda loose the 'transplant shock free' bonus. So I definitely need to work on my timings better to get the full benefit of using them.
Ease + Efficiency
I'm a little obsessed with finding perfect systems that are as efficient as possible, especially when doing anything by hand as I'm the queen of awkward, cackhanded slowness, so I need all the help I can get. At first I found soil blocks a bit on the slow inefficient side of things, but eventually as time went by I got better and after a few tweaks, I'd now 100% much rather make up (stand up) soil blocks than fill tray cells.
The biggest tweak I made was buying a concrete mixer to mix everything up dry & wet, if you're making soil blocks on any sort of scale I absolutely recommend it—it was the real game changer in terms of efficiency (and enjoyment). I only really have one more biggish step to having the seemingly 'perfect system' which is sifting the compost—I'm still doing this quite slowly with round soil-sifter thing, one day I'll DIY a bigger better sifter but for now I can survive this one slowness.
Another obsession I have is trying to do as much as logical 'from scratch'. I think I just don't fully trust the mass produced and love to put on my control freak and know the whole process. With soil blocks there isn't any pre-mixes available in NZ so the only option is to make up my own mix, which suits me just fine. I adapted Bare Mtn's recipe to what things I could easily find available in NZ. I'd love to understand a bit more of the science behind the different elements so I could have a better understanding of the recipe and how to tweak it to suit my needs better—but in the meantime I'm mostly happy with my naive adaption. I'm not sure if it's my mix or mostly likely my watering but I do get the odd tray that is prone to a bit of green algae growth.
Also my germination last season was leaps & bounds better than the year before, which maybe partially due to the soil blocks or possibly I just researched what everything needed a bit more thoroughly.
Other things I didn't think about
Soil Blocks + Water
As soil-blocks are held together by themselves and no container to contain them, they can't be watered overhead. This makes watering them in the propagation house a little tricky + hardening them off in the rain impossible.
For watering in the propagation house I've found the easiest way to do it without having them sit in water too long is to partial fill with water a leakproof tray and place a (webbed) tray of soil blocks into the water until they're hydrated enough, and the put the tray back in it's dry leak-proof tray. (Maybe for the bigger blocks I could possibly do away with nesting in the leakproof tray altogether). I normally have a few of these 'water trays' going at a time to make it a bit quicker.
As the soil blocks will wash away in the rain (and it rains a lot here in Stratford) I can't leave them outside to harden off. To make up for not hardening them off much at all I've started putting a fan on them to get them used to the frequent windy conditions, and after planting cover with mikroclima cloth over low hoops, which saves them from the worst of the wind, rain, sun, high/low temps (+ pesky birds) to help ease them into being outside. Which if planted out on time helps eliminate or reduce time loss to transplant shock.
What sized blocks?
I currently have 3 sized block-makers:
MINI 20—The smallest block by far. I thought this was going to be my favourite, and getting 300 little blocks on one tray is a space saving dream when it comes to limited heat mat /propagation house space. But as they're so tiny they just dry out super crazy fast when things heat up in late spring / summer, so I haven't really used them for a while. I did recently plant out the Mini's directly with a bunch of one cut wonders (bupleurum, saponaria etc) which I quite liked but as I was almost planting them out too early/little (crazy I know!) I added a layer of clear plastic to their hoop so they didn't get rained away. A couple of weeks later now they're looking so good, I might try it again—though I really should just suck it up and try direct seeding them.
STAND-UP 12—The largest block I have, with the little cube inserts they are amazing fast & fun to bump up the Mini's into. While they work great, I've stopped using them so much as all that space saving of the Mini's goes right out the window when they're bumped up to the 12's—1 tray of Mini's needs about 8 trays of 12's (36 per tray). I might however save using them for plants that are on a larger grid spacing, which are a bit slower going (rudbeckia) so I can have a bigger transplants but don't quite need as many plants.
STAND-UP 35—This was a last minute add on out of curiosity, and has been my favourite so far. It fits 105 per tray so it's a happy efficient middle in terms of space. They do tend to dry out a little faster than I'd like when it's sunny, and they really do need to planted out in about 4 weeks for most things. I've learnt the hard way to hold off sowing them until I'm 90% sure I'll have the bed space ready in time (I still often start them too early & they have to wait around too long, so I have to either start them again or plant out sad looking plants).
I am also about to add the STAND-UP 20 to my line-up which I'm hoping will bridge the gap between the 12's + 35's in terms of space/trays + drying out too fast.
Making the blocks
I make up a big mix dry and almost always have some stored ready to just add water when I need to, but I always leave a bit of dry mix to add back in incase I'm a bit heavy handed with the water. It's hard to explain the right consistency/wetness but for the most part not too dry & not too wet, it's probably best to experiment with it on wetter side and add dry mix back in and when they stop falling out all the time it's around there. If my mix is flirting with being too wet it's really helpful to make sure I twist the block maker as I lift it up, otherwise there's sometimes a bit of suction where I can sometimes annoyingly leave behind a couple of blocks.
I scrape the bottom of the block maker before placing & releasing into the tray, I'm not sure if I'm just making more work for myself but part of the soil block charm is the 'air pruning' of roots, which I figure if there's a layer joining all the blocks together at their bottom that must be counterintuitive right? Anyways I use a plastic plastering type trowel to do the scraping (the metals ones catch too easily when scraping).
I only really get a couple almost perfect constancy pressings (?) per batch as the consistency is always slightly changing. I prefer them on the slightly wetter side than the drier side as the drier ones crumble too easily when it comes to planting, if they're on the wetter side you can leave them for a day (or weeks if covered so they don't dry out) before sowing to firm up a bit more.
I've found the easiest way to label what's in each tray is to use a bit of low-tack masking tape down one side & write on that. I divide up the tray into groups of rows using the plastic trowel thing to move them slightly so the gaps are obvious, and plant no less than one 'row' per variety.
I use two similar but slightly different recipes for the Mini blocks & all the other Standard blocks. I like to use fine pumice in my mix but it could easily be mixed or substituted with perlite, and a little sand + vermiculite would also be fine as well. The biochar is totally optional, and it best left out while you wait for it to be 'activated'.
You can download my Soil Block Recipe PDF here.
Where I source things:
Worm Castings I couldn't easily find any locally & I don't have a worm farm so I bought some from Easy Grow
Compost I just use the same as I top my beds with.