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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 the Internet.

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 can help!
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 strong winds.

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 a reduced 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 this photo. More...

(right) Paul moves his cacti inside for winter...
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 light.
Just a fur ball or an evil spirit?
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 with their beneficial protection.

#1 consideration for a structure is wind proofing
My 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.

30% shade 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.
You need to research the average low temperature in your location. This one (right) is for my town in the Central Valley, California. See how interesting it is that there were lows of only 18 degrees in 1932 and 1949?

The averages are safe for my cactus. They can survive a night or two dip below freezing; it is when the temp stays below 320, for a long time, that causes damage.

Data from: http://www.intellicast.com

November full moon shining down on my joyful labor. While working on this Raccoony chased after chirping birds in the trees. She finally got one, a blue jay, and Bobcat was fascinated. He grabbed a wing to run off with and enjoy. When dragon flies are abundant in summer the cats chase them�leaping into the air, twisting around like ballet dancers, to grab the flapping insect toys.

Metal conduit is used to frame this, then 3/4" PVC pipe ribs fill in between. Fittings can be obtained from my favorite source Wonlim 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


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