Pest Plants
September: Week 39
by Teresa HannaSEVERAL years ago I asked readers of the Los Angeles Times to send me the names of garden plants that grew out of control. The subject came up because several things I had planted were suddenly trying to take over the place. We're not talking about weeds here, but things planted on purpose that soon begin behaving like weeds--invasively spreading underground or everywhere sprouting from seeds.
As an example of such as plant, I nominated a pretty thing with red and yellow tubular flowers named Lobelia laxiflora. It took only minutes to plant, but months to get rid of, after I realized how aggressive it was. In my opinion, nurseries should have a large warning sign posted next to it--similar to those at gas stations, paint stores and other places that dispense potentially hazardous chemicals--"Warning: May Spread Everywhere." It moves on fat white roots that can grow as deep as 14 inches underground, which puts them almost beneath the reach of a spade. As you dig, you can't help but break off little pieces of root, and all of these proceed to grow new plants. If this is sounding like bad science fiction, then you have the idea. I suppose this plant has its place--on dry slopes where little else will grow--but I will never let it back into my garden.You can try and cage plants like this, growing them inside bottomless buckets or tubs sunk into the soil, but I once tried this with a European ornamental grass named Elymus and it managed to escape. Nevertheless, some bamboo growers surround their spreading kinds (there are clumping bamboos that don't spread) with sheet metal buried at least 14 inches deep, and claim this works. But I suspect it has a lot to do with your soil. Plants aren't likely to send their roots too deep in a hard clay soil, but in good garden soil they might. I once grew a black bamboo that contentedly lived in one corner until I redid the neighboring lawn. Somehow it sensed all the great new soil nearby and took off. Weeks later, I found sprouts coming up 15 feet away, smack in the middle of my new lawn. It took days to get it out.
I think the worst offenders are those that spread widely underground, unnoticed by the gardener. But many who wrote were equally upset by plants that scatter seed a little too freely. Here, then, is a list of menace plants suggested by The Times readers. Each was mentioned in at least several letters, so it is not just one person's condemnation.
Japanese anemone (Anemone hybrida or Anemone japonica): One of the most reliable and pretty fall-blooming perennials for somewhat shady parts of the garden, it spreads deep underground, though slowly. In the right place it's great, but make sure you want it there for a long time, as it's nearly impossible to get rid of and will spread more than a few feet. One reader in Palos Verdes wrote, "While it was doing its thing above ground, it was much more active below ground."
Asparagus fern (Asparagus setaceus): "Just plain sneaky," wrote one Whittier reader. Seedlings spread by birds are surprisingly hard to pull out in one piece.
Night jessamine (Cestrum nocturnum): Powerful, almost sickly sweet scent in summer and seeds everywhere. As one reader described: "By the next day, what was bare dirt was now covered with two-inch seedlings."
Cashmere bouquet (Clerodendrun bungei): "It seems to sprout from ridiculously small pieces, and, worse yet, the crushed foliage smells like dirty socks," complained a Fullerton reader.
Pampas grass (Cortaderia selloana): A Santa Monica reader wrote that it has "nasty sword-edged leaves and a tough and horrid root system." Many conservationists suggest not planting it near wild areas since it may escape, like its cousin, Cortaderia jubata, which has become a noxious weed along the coast, scarring roadsides all through Big Sur and other formerly pristine areas.
Montbretia (Crocosmia crocosmiiflora): A beautiful, brilliant orange bulb that one reader said multiplies too fast so is "not worth the beauty." Indian mock strawberry (Duchesnea indica): "It chokes out everything in its way," wrote a Santa Monica reader. "Seedlings spring up everywhere and the roots spread like wildfire," which is probably why this strawberry look-alike was such a popular ground cover for a while.
Horsetail (Equisetum hyemale): Without a doubt, this plant, which looks like a bunch of spreading sticks, got the largest number of bad marks from readers. Keep it in a container, out of the ground, as it spreads wildly and is tough enough to have survived from the Carboniferous Age.
Female shamel ash (Fraxinus uhdei): A Corona reader wrote: "Its seeds are more prolific than rabbits."
Algerian ivy (Hedera canariensis): "My neighbors on four sides have it, and I am constantly fighting to keep it out," wrote a Covina reader, though at least it doesn't root deeply, so isn't that hard to remove.
Morning glory (Ipomoea tricolor): "I was warned by the nursery that I'd be sorry," wrote a Huntington Beach reader. "And they were right. It seeds everywhere."
Giant Burmese honeysuckle (Lonicera hildebrandiana): "I found it growing in flower beds 100 feet from the original plant," said a Palos Verdes reader.
Japanese honeysuckle (Lonicera japonica): "You think you have it all out and there it is again," said a reader in Carpinteria.
Four o'clock (Mirabilis jalapa): "They drop hundreds of seeds," a Cardiff reader said. "And the seeds are hard-shelled enough to survive time and chemical agents"--which is why it is seen growing in so many vacant lots.
Sword fern (Nephrolepis cordifolia): "Takes over everything," said a Santa Monica reader.
Mexican evening primrose (Oenothera berlandieri): "I find it a nuisance," wrote a Palos Verdes Estates reader, "but the flowers are very pretty," which is probably why it survives as a popular, pink-flowered spreading perennial in drought-resistant designs.
Ornamental oxalis (Oxalis purpurea): "It spreads by bulbs, seeds, runners--you name it," said a Costa Mesa reader. And though it grows only a few inches tall and completely dies down for the summer, it is very hard to get rid of because it has so many tiny prodigy, the white form of the'Grand Duchess' strain particularly so.
Virginia creeper (Parthenocissus quinquefolia, sometimes still sold as Ampelopsis): In Lancaster, a reader "filled eight bags with roots that had taken over the rose garden." Also seeds about.
Passion vine (Passiflora): Said a reader in South Pasadena: "I have seen it grow to the top of very tall pines and completely smother large shrubs in a jungle-like tangle. We found the little seedlings everywhere." A butterfly named the Gulf Fritillary likes it, though.
Fountain grass (Pennisetum setaceum): A Palm Springs reader wrote to tell us that "it's been banned by the city of Palm Desert." 'Nuff said. Golden bamboo and black bamboo (Phyllostachys aurea and Phyllostachys nigra): One reader said these running bamboos are as "bad as Bermuda grass, but a whole lot bigger." Some other bamboos clump and don't run.
Obedient plant (Physostegia virginiana): Another handsome perennial that spreads a bit fast and far, or as a Costa Mesa reader put it: "A misnomer for certain."
Pincushion flower (Scabiosa atropurpurea): "Never let the dried flowers go to seed!" cautioned one reader in La Caņada Flintridge. Cape honeysuckle (Tecomaria capensis): "Our landscaper put this in," one reader wrote, "and I could wring his neck! It has taken over a 400-square-foot area [from one plant]!" Another said, "Its tenacious tentacles are well on the way to an unfriendly takeover of our garden," and added that "tin snips are required to trim it back." Numerous readers complained about this common landscape shrub with the bright orange flowers and shiny foliage.
Rice paper plant (Tetrapanax papyiferous): "It is a real sorcerer's apprentice," wrote one reader. "I got rid of it by moving from Hawthorne to Northridge." This was another frequently mentioned pest; it also has a reputation for causing rashes.
Sweet violet (Viola odorata): A Los Angeles reader said, "My parents used to make me pull them up instead of writing sentences." Nothing sweet about the way it spreads.
Periwinkle (Vinca major): A Santa Monica reader cried: "It's taking over my whole garden!"
Though I would be suspect of any plant in this list, it is important to realize that not all people feel the same about these plants. For instance, one reader actually wrote and asked where he could buy the lovely lobelia I was having such trouble with! He thought it just the plant for his tough slope.
