A couple of years ago I started using soil blocks. They have a real learning curve to them. At the start figuring out how to make the block stick together right was hard. I finally started making the soil wet enough. Basically if you can't pick up a handful of mix and squeeze out a little water, it is too dry. I figured out that I should check to make sure the blocks formed well by pushing up with my hand on the bottom. Occasionally one doesn't have enough soil and it would fall apart. Instead now I find that wayward block and manually push in more soil. I've gotten much faster at it.
I also figured out how to water them easily. Most of the recommendation say use a spray bottle. You must be kidding. My hand would get so tired using a spray bottle. It would take forever and promote fungal diseases. Instead I made the system above. The bottom tray is just a flat, with no holes. Inside I put a mesh flat (the ones you get when you buy plants at a nursery). When I needed more of these mesh flats, I asked my friends for some. I now have a stack bigger than I need (thanks Noa!).
The blocks can't stay seated well on them. So on top of that I put screening. This keeps all the blocks flat. I can pick up the flat with holes in it and move it to a flat filled with water and set it there until the blocks are soaked through. Then I move it back to its own holeless flat again. Easy and fast. I think one addition would help even more. If I raised the mesh flat off of the holeless flat so there was some more airflow underneath the blocks, there would be better air pruning of the roots. Now occasionally the roots grow through the screening and run along the bottom for a short bit.
I do not use water straight from the tap. I let the water sit a day (like you would for your fish). This removes all the chlorine from the water. I think the plants grow better that way. Plants really hate tap water. Too many chemicals in it. It amazes me that we survive drinking it.
A soil blocker
Some people hate soil blocks and some love them. Their disadvantage is mainly the learning curve. Until you figure it out, the blocks can fall apart. Mine don't anymore (as long as I use tongs if I want to move them early on). Also it takes longer to plant up. I don't think in the long run they take longer since planting is much faster. I find it really hard to get transplants out of the plastic 6-packs. These I just plop in. Also there is no pot clean up at the end of the season.
One of the main advantages is the blocks don't get root bound they are air pruned. Plants can't grow after they become root bound unless you break up the root which severely shocks the plant. Though I do have issues occasionally when I put the blocks too close together and the roots from one grow into another block. I knife solves that problem easily enough. The other advantage is that there is no root disturbance when the blocks are planted. As long as they have been hardened off appropriately, they have no transplant shock.
And there are no little plastic pots to float around the garden all year long. Don't tell me you pick up all your pots when you should. I don't want to hear it. Mine tend to end up in a pile in the corner of the garden and then the wind blows them around. I also don't have to clean out the dirty pots and six packs. Have you ever tried to clean out a six pack? The brush doesn't really fit into them and they are so hard to clean out. I confess to using the dishwasher on occasion. But no more as I don't use them anymore. Ha!
Size does matter! Personally I love the 1 1/2" block. It is my favorite. Most go for the 2" blocker with the microblocker that fits right in to the 2" one. I love the idea of the latter system. Seed one seed in the small blocks. When they come up move them to a 2" blocks. But in reality I don't use it. The 2" blocks are too big for most of my transplants. I often transplant at 3 weeks for Asian greens and lettuce. And 3-4 weeks for other brassicas. The 1 1/2" is large enough to support that and fits 72 blocks in a flat. 2" blocks only fit half that number. The other major transplants that I do are my tomatoes and peppers. I prefer to start with a 1 1/2" block and transplant them into tall but thin newspaper pots. I think I might use the 2" blocker this year for the peppers though. I'm growing over 40 of them and the newspaper pots take way too long to make. So once again it might get use.
So how many of you all use soil blocks or have tried them? It is a big up front investment. I used the money my MIL gave me for my birthday one year as otherwise I wouldn't have tried them.