Once I started using soil block I never went back to other methods of starting seeds. I have tried them all, from plastic pots, paper pots, to growing in a flat. I found the seed flats caused too much destruction of the roots when you picked them out to plant and the plants would sit there doing nothing for a long time. The plastic pots took a lot of them and the would tear after a couple of years. You also have to store all of those pots in the winter. I feel that filling pots takes more time than making the blocks The paper pots were just too much work for me and you had to tear them when transplanting.
Soil blocks do have an start up cost because the block makers are not cheap but they are very durable and last a long time. Their are plans on the internet where people had made their own block maker but they usually make only one block at a time This would be great for someone who has a small garden but I make hundreds a years so that would be too time consuming for me. You also have to use the right soil mixture for the block to hold together and must take care with watering because you can erode the blocks. . I make a lot of the blocks in trays but I have also make blocks on large sheets of plastic in the cold frame and green house. This works very well and does not require all the flats. You will need a board or flat later to carry out into the garden for planting.
This is the time to make start my cool season vegetables inside. I do not have a heated greenhouse and the weather is too cold for the plants. I have began the Artichokes I am trying this year and cabbage. Shown below are two of the flats I have started. The one on the right I took off the cover to show the blocks while the tray on the left has the cover left on. The covers keep the moisture better for germination but if you leave too long you will have fungus growing because of the warmth from the heading pad.Not a fun thing to deal with. I do not have the lights hooked up yet but will have to as soon as they germinate or the plants with grow sideways and very long searching for light. It is best to avoid that.
They sell block in different sizes but I only use the 4 inch size and let them grow in the one. I found with blocks you can grow all types of vegetables, even ones that would not grow correctly with other methods because you do not disturb the roots at all or very little depending how long you keep them before putting them out in the garden. The only plants I usually do not use blocks are the root crops. I am thinking of even trying wheat and other grains this year.
For more information on soil blocks Johnny’s Seeds has a good reference page including a recipe for the potting soil.