I guess it depends on your scale. I have made 1.5" blocks and 3". In general they work well. I used them to sprout shrub/vine layer plants (3") that haven't germinated in place. A good example is yellowhorn, things I am paying through the nose for seeds. The smaller ones I used for perennials with big seeds (lupines and stuff like that) that also haven't done much in the wilds. For veggies they work sort of ok. They tend to fall apart after 3-4 weeks unless you compress them into a supernova, you have to have a wicking waterer I think and mine didn't work optimally. I think that was my fault for poor composition of my starter medium too. I went back to peat pellets this year because I changed my setup to include heat pads since I am in deep mulch and everything tends to be late germinating, but I'm doing some tests on the small blocks for the trays. Moisture content when you are making them seems to be critical, not too wet but pretty moist.
I would say if you are buying starter medium, you are not saving much versus buying bulk peat pellets at 10c a piece (I go through 600 at a time). I'm working on making my own bulk starter medium and potting soil from degraded wood chips using only waste stream items. For the starter medium especially under a cover it turned into a moldfest. So I am back to a more sterile starter plan for that.
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In case you haven’t looked yet, there are a number of YouTube videos of people who use or have used the soil blocks. It sounds to me like they’re best for home gardening use, but if you’re market gardening, then at least some folks find them impractical.
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This is my first year trying soil blocks and so far (only one crop planted) I would say I am at about a 7 on them. The root development is great, the lack of plastic is great, there is a learning curve as far as starter mix and moisture content but it's all stuff that seems like it can be figured out and dialed in. I can see the issues with them for commercial scale propagation but the benefits for lack of toxic waste (broken or 'contaminate' plastic pots anyone?) are tremendous. I also have not experienced the problems with watering that many people describe. I have been watering over the top with a focus on the driest ones, assuming that the extra that fills the tray is getting wicked up by everything else. I am also using home made compost as a part of the starter mix and there is lots of biology going on (any from the original batch that I haven't planted are now fairly dry and covered in an algae) but for planted blocks it seems to have been all positive.
I've had no success using them. They tend to fall apart long before the plant has grown large enough to transplant. I've messed around with various mixes of the potting soil and have used various strategies to get them to maintain their "block-ness", but they've been nothing but frustration and wasted seed for me.
I've found that using red Solo cups with a couple of holes drilled in the bottom uses 5 times as much soil than a soil block, but it gives the plant that much opportunity to grow before having to be transplanted. That's what I'd be having to do anyway if the soil blocks actually germinated and a plant started to grow --- transplant it to a larger cup before ultimately planting in the garden.
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I’ve used soils blocks for 2 years, was a great space saver for the amount I was growing, hundreds per variety, etc as I was selling starts and planting for scale.
However I find them impractical for small scale as I don’t need that many of anything in my gardens so I probably won’t use them this year.
I had great success with them though. I used pro-mix bx as my medium and used mesh bottom trays so had around 300 blocks per 1080 tray as I was using the 3/4” blocks. I set that tray in another that had channels and would bottom water and pour off any extra. That size block will dry out quick so daily watering is key.
Bare Mountain Farm has a great set up in their prop house with the mesh bottom trays sitting on wicking fabric that pull moisture from a wallpaper wetting tray. They have lots of instructional videos/posts that can be applied to crops other than flowers.
I really think it depends on what you’re starting, how much and your available space, etc whether they’ll be a benefit or not. I started a few hundred plants in a 72 cell tray as I can start 20-25 tomato and pepper seedlings per cell, I even start a few larger seeds that way just fewer per cell and then bump up when ready.
Thank you everyone for your inputs. Thank you Cindy as you were doing with the mesh bottom trays and bottom watering, what I was planning on doing. I figured that with the mesh bottom trays, the blocks would hold up longer by virtue of not be handled repetitively.
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