Kalanchoes (here K. daigremontiana) readily invade neighbouring pots and can be quite the pests!
You thought that by moving indoors to garden you were leaving the world of weeding behind? Well, think again. Like the weeds of our gardens and lawns, there are both weedy houseplants and houseplant weeds, plants that ready spread from pot to pot, seeking to take over the main plant’s space. And they really aren’t that rare. If you grow houseplants, you probably already know some of these plants already.
Here are a few of the plants that are often weeds indoors.
Baby plants crowd the kalanchoe’s leaf margin and readily come free.
Several kalanchoes (Kalanchoe daigremontiana, K. pinnata, K. laetivirens, etc.), all once formerly included in the genus Bryophyllum, have the curious habit of producing plantlets along the edge of their leaves. That is just soooo cute! And it gives you plenty of babies to share with your friends… but the babies readily “jump” into the neighboring pots and set up shop. They don’t actually jump, of course, but fall or get knocked free. Even so, when the pot next store fills up with the no-longer-quite-so-cute adolescent kalanchoes, there will be quite a bit of weeding to do.
Worse yet, kalanchoes are allelopathic: that is, they release toxic products that harm the plants whose pot they share. Thus, the desired plant grows less vigorously or may even die.
It’s better to put “jumping kalanchoes” in their place and not let them spread around indiscriminately!
Purple Shrimp Plant
Purple shrimp plant (Porphyrocoma pohliana)
This is a charming little houseplant in the Acanthaceae family with an as yet unresolved botanical name (Porphyrocoma pohliana and Justicia scheidweileri are on the short list). It’s certainly pretty enough, with shiny leaves highlighted by silver veins and a long-lasting red “cone” at its top from which the more ephemeral purple flowers appear.
This one just showed up in my plant collection one day, undoubtedly having hitched a ride in another plant’s pot. Now I find it all over the place.
Polka Dot Plant
Polka dot plant (Hypestes phyllostachya)
The polka dot plant or freckle face plant (Hypoestes phyllostachya), likewise in the Acanthaceae family, is a low-growing mound-forming plant with leaves dotted with spots and splotches in white, red or pink, sometimes to the point where there is little green visible, and likewise self-sows. The inconspicuous flowers often go sight unseen, but the baby plants that pop up here and there are much more readily visible.
Flowers of the spider plant (Chlorophytum comosum)
Who doesn’t know the spider plant (Chlorophytum comosum) with its long arching stolons (in fact, flower stems) bearing baby plants? However, unlike the kalanchoe, the babies aren’t normally invasive unless they happen to touch a pot of moist potting soil, as they don’t break free on their own. Instead, it’s the fairly insignificant small white flowers that produce pods of small black seeds that lead to small spider plants popping up in neighboring pots. They’re helped along by the fact that most people grow spider plants in hanging baskets, so their seeds can readily drop into any pots below.
Do note that any seedlings produced are all green, never bearing the cream to white stripes typical of most spider plant cultivars.
Orange spider plant (Chlorophytum orchidantheroides)
C. comosum is not the only spider plant that self-sows a bit too vigorously. The orange spider plant, confusingly known by several names, including C. orchidantheroides, C. amaniense and C. orchidastrum, sometimes modified by the cultivar name ‘Fire Flash’, can also be invasive. Nothing like its grasslike cousin, it forms a rosette of fairly broad leaves with an orange petiole and midrib and does not produce hanging stems. Still it blooms readily and its seeds can jump from pot to pot.
The same also goes also for the large-leaved spider plant (C. macrophyllum), another rosette type with large green leaves. It is, in fact, the most invasive of the three.
Madagascar jewel (Euphorbia leuconeura)
Most of the succulent euphorbias (Euphorbia spp.) stay in the pots you planted them in, but there is one exception: Madagascar jewel (Euphorbia leuconeura), with an erect swollen stem, eventually quite treelike, and oblong leaves with white veins, at least on young plants. The flowers are insignificant, but produce a seed pod that “explodes” at maturity, launching seeds in all directions, up to 15 feet (5 m) from the mother plant.
You often find this euphorbia in plant exchanges: people who have one always have plenty of babies to give away!
Grendelion (Dorstenia foetida)
This truly bizarre (and frankly, none too pretty) succulent in the fig family, Dorstenia foetida, produces one or more uptight succulent stems with a bulbous base and intriguing flat shieldlike flowers looking vaguely like a green sunflower. It too launches its seeds everywhere.
Umbrella palm (Cyperus alternifolia)
Also called umbrella sedge and umbrella papyrus, the umbrella palm (Cyperus alternifolius) is a popular grasslike houseplant that grows best when left constantly soaking in water. It has a characteristic whorl of narrow leaves at its stem tips. Under good conditions it produces a profusion of pale green flowers that turn brown over time and these release light-as-air seeds that germinate in nearby pots, producing little plants that look just like tiny clumps of grass at first.
Artillery plant (Pilea microphylla)
The artillery plant or artillery fern, Pilea microphylla, is not a fern, but the arching stems bear tiny leaves and flowers so small that you can scarcely see them without a magnifying glass. That doesn’t prevent it from invading the pots of other plants through its extra-tiny seeds, though!
Creeping Woodsorrel (Oxalis corniculata)
This trifoliate plant with yellow flowers (Oxalis corniculata) is strictly a weed: no one would ever think of growing it on purpose. Even so, this small Eurasian weed somehow made its way into commercial greenhouses at some time in the distant past and is now a common houseplant weed worldwide, especially in pots of cactus and succulents. It isn’t too strict about C&S plants though, and will move in on any of your houseplants if you don’t ruthlessly yank it out before it produces seed.
Holly fern (Cyrtomium falcatum)
Ferns produce lighter-than-air spores and therefore can travel through our homes on air currents. They can land anywhere, although most need moist conditions in order to sprout. They love my basement where I find them growing in many pots, especially in seed trays, where the high humidity is much to their liking. Among the species suffering from wanderlust are holly fern (Cyrtomium falcatum), ladder brake (Pteris vittata) and maidenhead ferns (Adiantum raddianum and others).
Whisk broom (Psilotum nudum)
This bizarre plant (Psilotum nudum) has no roots or leaves, only thin green upright branches that fork repeatedly and a creeping underground rhizome. Bunched together, the branches can be used as a small broom, whence the common name. Long classified as a fern ally, the whisk broom was recently determined to be a true fern, albeit a very primitive one. Its spores are carried about by moving air. Oddly, they germinate underground (most ferns germinate on the soil’s surface) and start their life as a parasite on soil fungus, a very unfernlike habit indeed.
Mosses in a flower pot
Yes, mosses also settle in our houseplant pots, most probably brought in from outdoors by the wind, as their spores are so small they can easily slip through window screens. Mosses mainly tend to appear in soil that is on the moist side, such as in pots of seedlings, but you’ll even find them in cactus pots.
Personally, I just let mosses grow: they create a nice green carpet that hides the soil from view and don’t harm their host. Terrarium lovers too enjoy mosses and often install various types in their miniature gardens.
Liverwort (Marchantia sp.)
Liverworts (Marchantia spp.) are closely related to mosses, but they’re much less welcome than mosses when they show up in pots. That’s because they form soil-hugging carpets so dense that the soil’s air circulation is compromised and that can lead to the pot’s main inhabitant to suffer from root rot. To get rid of liverworts, scrape off a ½ inch (1 cm) layer of potting mix and replace it with fresh soil. Be careful how you water, too, as the presence of liverworts often indicates overwatering.
If you grow houseplants, sooner or later you’re bound to find one or more of these invasive plants in your pots. It’s up to you to decide whether they are enemies to eliminate… or cute new plants that deserve their own pot!