ROBERT O'REILLY wrote:

how deep are raised beds to be?

That's a can o' worms!

Mine are 4' (2' above grade, 2' below it) ... but I am well at the extreme
end of things.

Try for at least 18" of loose soil below grade and an additional 6" (or
more) above it. With this arrangement, soil compaction from walking on the
path is dramatically reduced and plant roots grow unimpeded. Here in
Detroit, raised beds have an additional benefit that Pat didn't mention
(she lives nearby).

Frost.

Cool air sinks / warm air rises and I have found that the higher the raised
bed, the longer into the fall before a frost causes me problems. I have had
gardens that combined flat with raised with raised boxes and the raised
boxes were clearly better at evading the first frost or two. Next in order
were the (unenclosed) raised beds followed by flat beds sheltered by
overhanging trees. Flat beds simply failed at the first opportunity.

I have also found that raising a bed lets the sun strike and warm the sides
of it early in the spring and that the warming effect is cumulative. In the
early spring about 1/2 of my beds are shadowed by my garage and I notice a
decided difference in germination rates from one end of these 20' beds to
the other. The bean seeds in the end warmed by the sun germinated a LONG
time before the rest did. In fact, I had decided I needed to replant the
shaded end when I noticed that they were finally starting to sprout.

As the seaon progresses the sun is at a higher angle so less heat is
generated / plus the plants have grown and provide shade for the soil so my
soil doesn't get overly warm ... it gets to about 50-60 deg F and that's
about all.