I have several night blooming cactus that recently fell over, broken
through at ground level. They do not appear to be rotten or
dieeased, just got too heavy on a slope and broke off, i think.
How do I root and plant them? Just let a callous form and plant
several inches in the ground, or sand? Did they fall because my soil
is too hard and compacted? We have decomposed granite, but there is
sand in the wash. 
Thanks, and love your column. Kathy

I buy leather gloves in bulk and keep one pair  just for handling
cactus. I put on latex gloves underneath for extra protection. After
the leather picks up a lot of glochids, I toss them.

For all you gardeners in colder climates who have been growing your
cacti in pots outdoors over the summer, it's best to leave them in a
most sunny and sheltered spot until nights are almost frosty. Before
frosts arrive, bring them indoors into a very cool but sunny room.
They will need little if any watering or feeding although a small
amount of fertiliser high in potash often helps harden them off in
advance of winter dormancy. A secret to successful flowering is too
keep them as cool,sunny and dry as possible all winter, then in
early spring as days obviously lengthen and warm, again  apply a
small amount of potash or special cactus fertiliser and place your
cactus pots in the sunniest and warmest spot you've got and soon
you'll see buds popping out like magic! 

We have a huge and awesome Mexican Fencepost next to front corner of
our house. About 15 - 18 feet tall, about a dozen branches. The
thing is incredible. It was one thing we loved about the house
frontage when we bought.

Have had heavy rains past three days near Phoenix Az. High winds
today. The cactus toppled over - I guess the soaked ground, heavy
limbs due to big gulps after a dry year, and high winds did it. Good
news is the house caught its fall - will just have to do a little
stucco repair - came within 8 inches of the big front window - so
lucky there as well. So it is leaning at about a 50 degree angle.
Broke one branch.

How to put it back? I'm wondering if I could wrap several straps
around it, run ropes out to street and use truck to slowly pull it
back. Then stake it to three pegs.

Should I do this myself, or should I call a pro?

Also, we always wondered if they are supposed to be trimmed? Maybe
we have got the answer to that.

I’m so sorry to hear about your cactus. Working with mature clumps
like that is a challenge because of their incredible weight. One
also has to be careful not to gouge the tissue, which allows disease
to enter. Does your cactus have an obvious strong and expansive root
system that just got pulled out because of wet soil? Or is there
little or no root system to support it because roots rotted over
time, perhaps due to overwatering nearby for other plants? Also
consider its present location, as well as soil type. Is it always
going to be overly wet there from rain off the roof, for example? Is
the soil heavy clay that retains moisture and promoted root rot? If
so, it might be difficult to get your cactus to reroot securely and
another big rain (or just its weight) could topple it again. If you
really want to keep it intact, you might want to check with
landscape consultant Cesar Mazier at cmazier.com. As former director
of horticulture at the Desert Botanical Garden, he has considerable
experience with moving and transplanting heavy cacti. Another option
if getting your cactus back up on its feet doesn’t work out might be
to make starts for new cacti from existing arms. At the very least,
you can do that with the broken arm. Good luck and let me know how
it turns out!