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Mexican Fence Post Cactus
Lophocereus marginatus
Reviewed by Kiersten Rankel M.S.
QUICK ANSWER
Stem cuttings are the most reliable method and root in 4 to 8 weeks after the cut end is calloused for 2 weeks. Seeds give true wild-type plants and germinate in 2 to 4 weeks but take 3 to 5 years to reach a worthwhile size.
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Stem cuttings
Best for fast results from a tall column
From seed
Best for many true wild-type plants
Stem cuttings
Time
2 weeks callus + 4–8 weeks rooting
Level
Beginner
Success rate
High
You'll need
Sterile sharp knife or pruning saw
Heavy gloves and tongs
Newspaper or cardboard for callusing
Cactus or fast-draining mix
Deep terra cotta pot with drainage
Bright sunny spot
1
Cut a 6 to 18 inch section
Choose a healthy column with no soft spots or scarring. Cut straight across with a sterile knife or pruning saw. Wear heavy gloves and use tongs to handle the piece since the spines are sharp and the column is heavy.
2
Mark the upright orientation
Use a marker or piece of tape to flag the top end of the cutting before you set it down.
Mexican Fencepost only roots from the bottom end and will refuse to root if planted upside down, so this small step prevents a frustrating mistake.
Mexican Fencepost only roots from the bottom end and will refuse to root if planted upside down, so this small step prevents a frustrating mistake.
3
Callus the cut end for 2 weeks
Stand the cutting upright on newspaper in a dry shaded spot. The cut end needs to dry to a hard tan-colored scab before going into soil. In humid climates this can take 3 weeks, so wait until the cut feels firm and dry to the touch.
4
Plant in a fast-draining mix
Fill a deep terra cotta pot with cactus mix amended with extra pumice or perlite. Push the calloused end 2 to 4 inches into the dry mix. Use rocks or stakes to brace tall cuttings since they tip over until roots anchor.
5
Wait a week before watering
Place the pot in bright indirect light at 70 to 85 degrees F and do not water for at least 7 days. The cutting draws moisture from its own tissue while it sets roots. Watering too soon causes rot at the base.
6
Water lightly and check for roots
After the first week, water sparingly when the top inch of mix is dry. Give a gentle wiggle at 4 weeks to test for resistance.
Once rooted, move into full sun and water on a normal cactus schedule of every 2 to 3 weeks in summer and once a month in winter.
Once rooted, move into full sun and water on a normal cactus schedule of every 2 to 3 weeks in summer and once a month in winter.
WATCH FOR
Black or yellow soft tissue spreading up from the base. This is rot from skipping the callus step or watering too early. Lift the cutting, cut off the rotten section above the damage, callus again for 2 weeks, and start over in fresh dry mix.
From seed
Time
2–4 weeks germination
Level
Intermediate
Success rate
Moderate
You'll need
Fresh Mexican Fencepost Cactus seeds
Shallow seed tray with clear lid
Cactus seed mix (sterile)
Fine mister or spray bottle
Heat mat (optional)
Bright indirect light spot
1
Source fresh seeds
Use seeds less than a year old since cactus seed viability drops fast. Buy from a reputable cactus seed supplier or harvest from your own ripe fruits. Old or improperly stored seed gives germination rates near zero.
2
Sterilize the mix
Bake cactus seed mix at 200 degrees F for 30 minutes to kill fungus spores, then cool completely.
Damping off is the main killer at the seedling stage and a sterile mix is the best defense.
Damping off is the main killer at the seedling stage and a sterile mix is the best defense.
3
Sow on the surface
Fill a shallow tray with the cooled mix and pre-moisten lightly. Sprinkle seeds across the surface without burying them. Cactus seeds need light to germinate so do not cover with soil.
4
Cover with a clear lid
Place a clear dome or plastic wrap over the tray to hold humidity at 80 percent or higher. Set in bright indirect light at 75 to 85 degrees F. A heat mat speeds germination if your room is cooler.
5
Mist when the surface dries
Check daily and mist the surface lightly when it starts to dry. Tiny green specks appear in 2 to 4 weeks. The seedlings look like green pinheads at first and develop spines around 8 weeks.
6
Grow on slowly
Vent the dome gradually starting at 8 weeks until the seedlings tolerate room humidity. Keep them in their tray for the first full year. Pot up to individual cells only after they reach an inch tall, which usually takes 12 to 18 months.
WATCH FOR
Seedlings that flop over and turn translucent. This is damping off from a wet medium or unsterilized mix. Increase venting immediately, mist less, and start a fresh tray with sterilized mix if losses keep mounting.
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About This Article
Kiersten Rankel M.S.
Botanical Data Lead at Greg · Plant Scientist
Editorial Process
Propagation methods verified against Lophocereus marginatus growth data from Greg's botanical database, cross-referenced with USDA hardiness zone data and published horticultural research.
398+ Greg users growing this plant
USDA hardiness zones 9a–11b
Citations:
Royal Horticultural Society
Royal Horticultural Society