Friday morning I was busy in the laundry room where I keep my seedlings. My lettuce seedlings had their first true leaves. The roots were coming out of the bottom of their little tiny soil blocks. It was time to pot them up. I've had questions about what soil blocks are and how I use them. So I'll use my lettuce as an example.
I have three soil blockers. The smallest one makes 20 blocks all 3/4"x3/4x3/4"". They are so tiny. When I use these blocks I put just one seed inside each. If they don't germinate (like you can see for some of the lettuce above), they just get tossed. They don't take up much soil so it isn't much of a waste. They are great for using every little seed you have, but they dry out very quickly. I have to water them very often compared to the bigger blocks. These little blocks pair with my largest blocker. These larger blockers make soil blocks 2"x2"x2". Mine have inserts (which you buy separately) that punch out holes for the 3/4" blocks. So once they have a true leaf, I just put the little blocks inside the bigger ones. Potting up is so easy.
The medium ones are 1 1/2"x 1 1/2"x2". These are my favorite size. The 2" size takes up a lot of room. They can be crammed five across, but it doesn't leave any space between them (I need one that is just 1/8" short of 2"), so the roots will grow together into each others blocks. This is not ideal. For some plants I'll have to place them only four across which takes up a lot of space. The 1 1/2" blocks fit six across with a lot of space between them. Perfect. The issue with these is that I always put in at least two seeds so I have to thin. Not really much of an issue. I will still use the other ones for things that need a bigger pot, like tomatoes and peppers. I'll also use them for things that I don't know the germination on or things that I don't have much seed for.
Soil blocks have a great advantage of not having transplant shock (just like newspaper pots but faster to make). I don't have to wash out pots every year. No plastic, which is always good. Nothing thrown away. Their disadvantage is that they have a learning curve and if you are too rough with the blocks they can fall apart on you. I use tongs to move mine and bottom water so the soil doesn't get washed away.
Here are my lettuce seedlings all potted up. I have a whole box of Popsicle sticks from when my kids were young. I use them to label all my blocks. In a couple of weeks they will go into the garden. I think lettuce from now on will stay in the 1 1/2" blocks and I'll save the bigger ones for things that need it. They take up way too much space. But these will be outside quickly so it isn't too much of a problem this time.