Steve B wrote:
I live in a dry desert climate. What can I do as a preventative to garden
tool wood handles splitting? And after they're split, I need to sand them
down and do .......... what?

If you're emotionally attached to the tools, then you're involved in
one of those maintenance relationships. Periodic dressing with your
choice of oil will keep the wood moisturized. As far as the splits,
it depends on how bad they are. Wood filler would tend to crumble out
as the tools are subject to a lot of flexure and heat/water stresses.
You could caulk the gaps before you oil them the first time. Wipe off
the excess with a damp rag and wait for the water to evaporate out
before oiling them up.

Or you could end the maintenance and buy fiberglass handled tools.

R