I've mentioned before that with gardening there are many ways to do things. This is certainly true for starting new plants. Direct seed or transplant? If direct seeding, how many extra seeds? Then are the seeds planted in a tighter spacing than ultimately desired, and then thinned to the desired spacing, or multiple seeds planted in stations at the desired spacing, and then thinned to one per station? If transplanting, plug trays or soil blocks? Transplant the plugs or soil blocks directly into the garden, or into larger pots first? Just a few of the many decisions to make. We like to start as many different types of seeds as we can indoors, in flats, and then transplant the seedlings directly into the garden later. There are some exceptions such as beans, peas, and radishes, which get direct seeded. Also, the past couple of years we've changed from transplanting squash seedlings to direct seeding squash seeds. But for the most part, we have better success with transplants. We feel that the extra work is worth it. On the other end, we usually transplant our tomatoes, peppers, and eggplants into 4" pots for further growth, before putting them into the ground in our rolling greenhouse. But most of our seeds are started in flats indoors and then transplanted directly into the garden.
We make soil blocks using a hand-held soil blocker, that was designed by Eliot Coleman and is available through Johnny's Selected Seeds. It works great. The only thing we've changed on it was to add some rubber tubing over the handle to make it a little easier on the palm of your hand. They also sell mesh trays which hold 50 soil blocks and fit into standard 1020 trays. We've tried a number of different potting mixes, but the one we like best and always use now is Pro Mix Bx with mycorrhizae. However, after the soil blocks are made and placed into trays, and then filled with seeds, we cover the seeds and fill in the dimples in the blocks using vermiculite, instead of the potting mix. The lightweight vermiculite seems to allow the dicotyledons to push up through easier, especially with the really tiny seeds.
When we are ready to transplant the seedlings we use a couple of special tools: one store-bought and one home-made. Because the soil blocks are 2" square, we use a 2" wide mason trowel both to lift the blocks out of the trays and also to dig the hole in the ground for the seedling. We find this much easier than using a standard garden trowel.
Our home-made tool is for spacing. On larger spacings, like 18", which we use for brassicas (broccoli, cauliflower, cabbage) and solanaceaes (tomatoes, eggplant, peppers), we simply stretch out a tape measure the length of the bed. We use the tape measure on spacings down to 8" (lettuce, fennel, chard). But for distances less than 8", we've found it easier to just use spacer blocks from plant to plant. We've made them at 6" (for spinach and onions) and 4" ( for beets). We took a scrap piece of "one-by" wood and ripped it to 2" wide, then we cut it to the length of our plant spacing, either 4" or 6". Then we cut a shallow kerf 2" from one end and drilled a hole through the middle of the 2" square between the kerf and the end of the board. We duplicated the kerf on the other side so the spacer can be used on either side. The drilled hole represents the stem of the last seedling planted, and the square between the kerf and the end represents the soil block of that seedling.
To use the spacer, we simply align the drilled hole with the stem of the last seedling planted, and then we use the trowel to pull a hole in the soil even with the end of the spacer. The trowel is exactly the width of the soil block so the hole doesn't need to be very big. We cover the beds with about 2" of compost before planting, and using this method, we are able to plant the seedlings without disturbing the compost cover over the soil. Almost no soil from below the compost ends up on top of the compost.
For 2" spacings (green onions, 5 seeds per block), we don't need a spacer. We just butt the soil blocks next to each other.
These simple tools help us transplant our seedlings much quicker and more efficiently.