Here you'll learn about and recognize succulents and cacti that become weedy, invasive nuisances if you make them too happy, and what to do about them. Keep in mind---as I explain elsewhere on this site---that your region, your garden's microclimates, and the time of year make a big difference as to which succulents are ideal or pose potential problems.
Avoid weedy succulents
Controlling invasive succulents can be as simple as not growing them to begin with. (How do you know which ones? Well, keep reading!) Unlike annual weeds---which sprout in spring and are suddenly everywhere---most succulents are perennials.
Like all plants, succulents bloom, but not necessarily annually. When they do flower, they typically don't send forth a lot of seeds. Nor do their seeds always sprout (most don't).
A "Good" Succulent Weed
Purslane (Portulaca oleracea) is both a vegetable and an annual weed. The taste is similar to watercress, so use it as you might spinach or lettuce. It's loaded with vitamins, minerals and antioxidants, and is higher in Omega-3 fatty acids than other greens. I occasionally run across it when weeding my garden, so do watch for it in yours. Or start it from seed. Use it as an ornamental filler for succulent container gardens, hanging pots and window boxes. Discover more edible succulents.
Unwanted pups: What to Do
Succulents that spread by underground runners---roots that grow parallel to the soil, just under the surface---produce clones that turn green (photosynthesize) when they break into sunlight. Parent roots, like umbilical cords, feed the offspring until they're established.
Pups of small succulents such as haworthias and dwarf agaves are seldom a problem, in fact, are usually welcomed.
However, pups of large succulents have to be dug up if unwanted. This tends to be typical of large agaves.
Like a protective mama bear, a mother agave has claws---thorny spikes along leaf margins. These make it challenging to remove offspring beneath Mom's leaves. Don't delay pup removal; all too soon they're big enough to fight back.
Most agaves pup. Among those less prone to do so are Agave victoriae-reginae, Agave 'Blue Glow', Agave guiengola, Agave ovatifolia, and Agave 'Sharkskin'. Learn more about agaves on this site and in my YouTube video: Agave Essentials and Essential Agaves.
Meet an invasive aloe
A common aloe that propagates by underground runners is Aloe maculata (formerly A. saponaria). About a year after planting it in a flower bed, I found pups three feet away. The soil was soft and friable, so I'd grab a pup, pull on it, and along with it came a long lateral root leading back to Mom...who looked the other way.
I moved the colony to a less hospitable part of the garden and planted it in native soil (clay and decomposed granite). They've been there ever since, spreading much more slowly. Because they're free for the asking and not especially attractive (except in bloom) I call them "trash aloes."
Too many offsets?
Fairy crassula (Crassula multicava) grows offsets (baby plants) on its flower spikes. I produced an article and video about it a few years ago: Grow Shade-Loving Fairy Crassula: A Succulent Ground Cover You'll Love.
A recent comment on my You Tube channel surprised me, but perhaps it shouldn't have:
Tiny plants on floppy bloom spikes form at the base of dainty fairylike flowers. As these grow, ever-lengthening stems lower the plantlets to the ground. If they land or fall off on good soil, they may take root.
It's a brilliant strategy: The offspring---now a foot or so from their parents---don't compete with them for light or nutrients. Hence, a fairy crassula colony has the potential to spread endlessly.
Like fairy crassula, these produce plantlets that drop off and root. Unlike fairy crassula, which produces plantlets on flower spikes, those of mother-of-millions fringe the leaves.
Tall, pendant, tubular orange-red flowers are a bonus that makes the plants' weedy quality worthwhile (especially for those of us who have trouble growing them). Typical of kalanchoes, they prefer a maritime climate.
Succulents that break apart and root
Stem succulents start readily from cuttings, but most don't fall apart in order to do just that. These cacti are prized in some regions, reviled in others:
Eve's needle (Opuntia subulata or Austrocylindropuntia subulata) is my least favorite succulent---possibly my least favorite plant. It grows vigorously, isn't choosy about soil or other conditions, and falls apart if someone sneezes 10 feet away.
Eve's needle has vicious, concealed, hooked spines that latch on to anything they can, thereby traveling with the victim and leapfrogging the colony. This is what chollas do---a common name is "horse cripplers," but Eve's needle is especially happy west of its native desert habitat. Unwitting homeowners have spread it throughout Southern California.
If you see Eve's needle in a nursery, don't buy it. If you own a nursery, please don't sell it. If you already have it, get rid of it; all too soon, it'll be tapping on your windows.
Opuntia (paddle) cactus
The many species of Opuntia have in common pads shaped like ping-pong paddles that grow and spread one from the another. Each pad is capable of rooting where it falls, not merely from the point where it was attached, but also from any of its areoles (growth tissue at the base of spines).
Native to the desert Southwest and Mexico, opuntia has many uses, from edible nopales to security fencing. So there are "pro's" to its "cons." However, some species are causing major problems in Australia, where no cacti are native. I found an interesting list of those that are harming Australia's economy and therefore are illegal to sell or own, on the Queensland Government site.
It distresses me to include a gorgeous succulent, but this one has outworn its welcome. Specimens that start out manageable grow too large, then endanger owners and gardeners attempting to trim or remove them.
Milky latex sap that drips freely is sticky and caustic. An allergic reaction to it can send people to the hospital, especially if they get it in their eyes.
Yet, as noted earlier, one person's weed is another's treasure. This YouTube comment-question puts it into perspective:
You don't see yuccas springing up in gardens where they weren't planted. These super tough succulents do the opposite: Sit quietly in situ and grow and grow. (I'm referring to Yucca species, not ornamental cultivars such as 'Bright Edge' and 'Color Guard', which stay manageably small.)
After a decade or so, their swollen bases may encroach upon and split the seams of walls, terraces or (God forbid) pipes and your home's foundation. I have no idea how old the magnificent Bay Area specimen is in the photo, but I'm guessing it was planted well over a generation ago. Hopefully it won't cause trouble; it seems far enough away from the house behind it.
Know of a weedy succulent I haven't included? Do tell us about it in a comment below. And I'd be grateful to know your own experiences with any mentioned above!
Related Info on This Site
Before planting spiny succulents, weigh the pros and cons. Although they have a certain beauty, they can be dangerous and devilishly difficult to remove. Know how large one gets and position it where it can’t harm you, kids, pets, or passersby.
In both English and Spanish, landscaper José Arias explains and shows how to prune and handle Euphorbia tirucalli ‘Sticks on Fire’, a beautiful succulent with toxic, milky sap.
You’re already wary of poison oak, cactus glochids and the milky sap of euphorbias. Add agave sap to the list. In susceptible individuals, it causes the skin condition “agave dermatitis.”