Kudzu, this is a good question. My experience--and I recently saw a youtube video on the subject which examined roots on end-of-season tomato plants--is that if planted straight down with most of the stem buried roots will form primarily in the area right below the soil (in addition to the original root ball, now deeper in the hole), and NOT, or certainly not as much, all along the stem, as is sometimes thought. I suspect this has mainly to do with soil temperature. By this logic, a tomato planted using the trench method would be more likely to develop roots all along the stem. Whether there's much advantage to this, I don't know. But my practice tends toward the "ditch" method, though starting with the original root ball well below a couple of inches down, but not as deep as with what I call the "straight down" method. Actually, they seem to do well using either method. But let us hear your experience.

Gary

Does the ditch method take up a lot more room? Do you prune the 'down' side? I am trying (not very successfully) to visualise. Wouldn't that give it a shallower root system?

I prune any leaves that will be below soil level. Some don't, some do.

I try to time sowing seed so that I have about 6-9 inch tall seedlings to set out after hardening off around the first of June b'c the smaller the plant the quicker it can adapt to inground conditions.

But there have been those years that b'c of weather my plants got much bigger than that, sometimes 2 ft tall but never as tall as 3 ft. And since I used to grow many hundreds of plants and varieties each year there was no way I was going to dig holes deep enough to set those tall plants deeply.

So I trenched them. Just make a shallow trench about 3 inches deep with hoe or trowel, place the plant in it laying it down horizontally, no need to trim off anything, and cover up with soil, tamp down and water in to remove any air pockets. Leave the top of the plant sticking out, at first it will droop down but then stand up tall and straight in a few days.

Look at your rows and make all of the trenched ones planted with the same orientation and you still keep the distance between plants the same. For me that's 3-4 ft and 5 ft between rows.

So for me, putting out plants less than a foot tall means planting vertically, but plants over that size by quite a bit means trenching them, which actually happened very seldom for me.

Plants that are planted vertically are also going to have small feeder roots near the top of the soil and those trenched will also form deep roots.

I'm linking below to an old article that I think explains it very well and was done back in the late 20's when there was no molcular biology to deal with and the basic traits of tomato growth were studied.

Scroll down to the tomato section.

Carolyn

Here is a link that might be useful: Root structure