Any thoughts on this idea?

I want to start lots of seedlings for my garden and for sale. However, the problem is that 1. pots tend to dry out. 2. plant's root tend to circle round the pot. I know there are fancy ways to get around 2. However, I have an idea to get around both. Please let me know what you think of it.

I would have a styrofoam insulated cold frame, dug down two feet underground, and built up a foot above ground. A heating cable would be laid down on the floor. Then a grid of cardboard would be put in place, like what is seen in wine boxes but on a larger scale. They would be filled with potting mix. This would take up the bottom foot. Then small seedlings or seeds would be planted in each. By the time I was to remove them, the cardboard would be pretty soft, but the roots should have stayed in the right shape more or less, and the connection to the ground and the larger mass of the bedded plants should have counteracted the tendency to dry out. I would then be able to remove each plant and place it in a recycled plastic container for sale or transport. To keep the cardboard from wicking away water I would have capped the top edges of the cardboard grid with plastic tape.

I might also plant a few clovers in each cell to help keep the whole thing together.

I would not use this method for plants that really resent root disturbance.

I know I could use soil blocking, but that takes special potting mixes and the proper equipment. And if I set them on the ground, they would grow into the ground, and disintegrate when I tried to move them. If I set them up on a shelf, they would dry out.

Any comments are welcome.

Maybe a bottom up watering where pots are sitting in a tray? Maybe do the same thing, but with your plants in more stable pots instead of the cardboard grid.

I'd worry about inducing transplant shock twice... you might sell plants, but have lower growth rate...

If you are just transplanting, I grow in 1x2x.5 foot flats and just use a knife to cut our transplants, discarding the small and weak... but not for sale. I can miss a day.

I usually only have the drying out problem once the plants are well developed... so selling right before they fill the pot with roots is a good idea... most nurseries sell vege starts that are way too old and pot bound.

Finally, consider adding some soil to your potting mix, making the mix heavier, but slower to dry.

Automatic irrigation systems are simpler than they might seem, and work great with flats of pots, but you have to pay for a controller and valve up front. As a project, you can likely get someone with some landscape experience to set up a system for you.

For me your setup seems to be very complicated. If I remember that right, when I was a kid salad seedlings were sold wrapped in newspaper. They simply sliced through them I think they were grown together in a box. Maybe you try to ask an old gardener from the pre-plastic times. they must know this. I bet they had no soil blocker. Instead of heating you can go with a muck bed it heats by decomposting it does not cost anything and you won't get zapped.

I would go with a compost heated hot frame, but THEY seem complicated. To much ammonia or CO2, not enough heat, no heat once it dies down, etc. John Seymour considered them an effective technology, but hard to get right.

Also, tomatoes and peppers are more delicate than salads.

Are they going to get enough light? Every time I have tried something similar to what you are proposing, I end up with leggy starts -- long and very weak stems. I have had much better results planting seeds in large diameter plastic pots (10"-12") where they have enough mass not to endure wild temperature and moisture swings. Being in a bigger pot means that they can also get more natural sunlight instead of sitting down inside some protective well that cuts off a lot of the light.