Can I grow San Pedro outside?
||San Pedro can be grown outside in Zone 9
Tall, relatively thin cactus will freeze in cold
climates. There can be minor tip damage or complete
death—depending upon how hard the freeze is and how long the
temperature stays below 320 F (00 C).
To learn how cold it is in your region use this map from the
United States Department of Agriculture (USDA).
Even in a safe area like the San Francisco Bay there was
a memorable freeze for 3 nights in 1989 that turned many of
my San Pedro tips black (dead). The plants simply grew
offsets in the spring; but the point is that unusual low
temperatures occur. You can search for historic averages on
My plants are in California's Central Valley—Zone 9—so that is all I
know about; I don't have experience with any other zone.
How about building a greenhouse? Yeah, that
|2 ideas—a covered deck
& a basic greenhouse
At right is my deck, an old 15' x 25' one that I first sprayed
with 3 gallons of wood preservative. Floor is covered with a
white 14 mil tarp. Railings were converted
to shelves with scrap 2"x6" redwood given to me.
A frame above was constructed; all held together by
3" deck screws driven with my portable 9.6 volt Makita.
3/4" PVC pipe was used for the ribs. 20' sections of
sprinkler pipe were hot glued together making a single 40' pipe
that spans the whole deck. Tension
them over the wood frame and drive 1.5" deck screws to hold
in place. Trim excess with a ratcheting cutter. PVC cross
pieces also need 1.5" deck screws at the intersections to
prevent movement in wind (first cable tie them to set
position). Use lots of ribs so its sturdy to hold up to
6 mil thick greenhouse plastic, 20' wide is pulled over the
frame. Secure it with 1" hex head roofing screws that have a
metal washer with a neoprene one under it (image of one
below). They work great! That rubber
washer holds the plastic down perfectly. Over the plastic
pull the 20' wide, 30% shade cloth. This is necessary to
prevent sun burning the plants while also holding the
plastic down in high winds. Shade cloth is
sold at nursery supplies. The one near me,
AHS, has 100' rolls but
they sometimes have remnant pieces of various length (30', 60' etc.) at
price. Nice folks. Click for a larger view...
|Easy way to turn a deck into a
greenhouse. I love it! So do my cats who hang out
there when it is raining. Click for a larger view...
|(above) see the snow
outside? Jesse in Canada sent
moves his cacti inside for
|Here is a seedling house I built in 2008.
This is an unheated greenhouse, but these structures help
buffer temperature. The black floor as well as the mass of
plants/soil/water all keep it warmer at night. You can use
thermal mass storage (such as a north wall of stacked, black
painted water barrels) to prevent freezing. Or earth filled
car tires, etc. Or just move to California like I did.
Cactus seedlings are germinated inside under lights, then grow for
a year before transplanting to 2" pots and moving outside to
a shady location. Later they get up-potted and adjusted to
full sun under 30% shade cloth so they can
grow big & fat.
Horticultural or Agricultural supply
Greenhouse plastic (try
AHS) is sold
in 100' rolls (20' wide) for about $160. It is 6 mils thick but really
good stuff because its soft/flexible—won't tear or rip. Guaranteed
for 4 years. This project required about 35 feet from a roll. The
length faces south, nestled along a row of huge eucalyptus trees.
These had to be cut back. The north side back panel is white 14 mil tarp to reflect
|Just a fur ball or an evil
Never underestimate the value of cats as guardian spirits. If they are Angels
(you have to be worthy), and you're an enlightened cat pack leader, you
may be blessed
#1 consideration for a structure is wind proofing
location had a 60 mph wind storm last year. It was so powerful it
blew down one of the eucalyptus trees—another reason why I
pruned off much of their overgrowth last summer. This seedling house has 8 posts
pounded into the earth to anchor it from blowing away.
cloth is tightly stretched over it to prevent the plastic from
flapping which might cause it to fail. Anything that flaps will
eventually be tattered by the wind. I have to replace the flags
flying on the farm every 6-months as they tatter into pieces.
Wind is a powerful force. Like cats, only it blows.
Metal conduit is used to frame this, then 3/4" PVC pipe ribs
fill in between. Fittings can be obtained from my favorite source
International. 2x4s are an inexpensive way to form attachments
to screw down the ribs (1.5" deck screws). Deck screwing the PVC is
simple, it doesn't crack.
The 45 degree elbows are not the correct
angles but you can simply bend the pipe down, then screw it. Cable
ties are used to set PVC cross pieces to maintain the spacing but
have to be screwed with a 1 1/2" deck screw or they will move out of
alignment in wind storms.
Attach the greenhouse plastic with hex head
1" roofing screws (right) with a neoprene/steel washer (Western States
hardware at Home Depot). Those work great! Easy to drive with
a drill. I even drive them through the sheet plastic into the PVC pipe.
That neoprene washer is a wonder.
Inside are shelf units 24" wide. I buy those plastic ones from
Home Depot ($55). TIP: Drive a screw through each tube joint during
assembly so they
don't come apart when moved.
|Neoprene washer, hex head, roofing screw