I have always planted my tomato seedlings deep in the soil, with just
the top leaves above ground and everything else below. My
understanding was that the tomato would root the whole length of the
below ground stem so that this method would produce a super root
system making the plant less susceptable to variations in water
supply.

Yesterday, after we finally got our first frost (late two years in a
row now) I yanked all the dead plants. The tomatoes had indeed
develeoped roots on the below ground stems but only within the top
inch and half.

The original seedling root at the bottoms were well developed but the
only other root in the top inch and a half were very week. This is
not what I expected.

My soil is very deep sandy loam with lots of organic material
resulting from years of applying manure and compost.

Any thoughts on this?

TIA

John