We gardeners are always looking for tough plants. And those of us who are pursuing the elusive “sustainable garden” are searching for Colorado-adapted plants that do well with little or no care. But that is not enough. A sustainable garden is one where there is a balanced ecosystem of plants that can change as conditions change, to favor first one species and then another, but no plant should take over the entire space. Those dominating plants are the ones I call real weeds: the garden bullies.
Many gardeners would agree that it is better to wish all your life for a plant you can’t grow, than to have a plant your whole life you wish you could get rid of. So in this article I’m going to warn you about some plants that are often bullies in the garden. These plants are dangerous because they flower and look pretty enough in the beginning, but just give them room and a little time and LOOK OUT!! Some of them can be valuable plants in harsh conditions where little else will survive or where they are isolated, but some are invasive in Nature, and some are such thugs that putting them in the garden is like inviting the Hell’s Angels to your dinner party.
Euphorbia myrsinites, commonly known as Myrtle Spurge or Donkey Tail Spurge, has been classified as a noxious weed in Colorado because it has invaded Nature, but it is also one of the most pernicious garden bullies. The plant is quite attractive with its fleshy, bluish leaves forming spirals of foliage which can stand up or trail along the ground about 8″ high. The tiny greenish flowers bloom in early spring and are eclipsed by showy yellowish bracts in umbrella-shaped clusters. And though it makes a tough, xeric, attractive plant, it spreads far too fast both by seed and by roots !!!
As if this were not bad enough, the white milky sap that oozes from broken or cut stems is quite toxic. One hot summer day I helped a gardener remove a whole patch of this plant. The man who was working with me must have wiped the sweat off his face and got some sap on it, because the next morning his eyes were so swollen, he couldn’t see for half a day. Later, I warned a woman with a four-year-old about Donkey Tail Spurge that I saw in her garden. She told me she had just found out about it as her son and his entire pre-school class had to go to the hospital when they were playing “magic potion” with the milky sap. So if you are removing it, wear gloves and long sleeves and wash yourself and your clothes immediately afterwards. Because of this toxicity and because Myrtle Spurge is moving rapidly into our wild areas, this plant should be regarded as Noxious Plant #1. Remove any you have and encourage your friends and neighbors to do the same; it may take several years to succeed.
Nearly everybody has seen Snow on the Mountain, Aegopodium podagraria ‘Variegatum’. It is very attractive in the spring with its gray-green leaves with irregular, creamy-white margins; and also in summer when it blooms with flat, umbrella-like clusters of small white flowers. After flowering it often crashes and looks messy. Whereas it can spread by seed, the real problem is the deep and persistent roots. If you dig out a truckload, you will not kill the plant and it will be back the next year. In rocks I’m sure you could never get rid of it without an herbicide. Solarizing it under clear plastic for the months of July and August might kill it. If it reverts to the solid green form (which it is wanton to do), it is even more aggressive and hard to remove. I have seen this plant used as a groundcover between cement barriers, as between the sidewalk and the street. There it looked contained but could still seed itself. I call Snow on the Mountain a complete bully, because it wants the whole garden to itself, and a dangerous guest because it is so hard to remove.
Not many ornamentals are weedy in my dry gardens, but Ground Ivy is. Glechoma hederacea, a.k.a. Gill-over-the-Ground, or Runaway Robin became such a fast spreading thug in my landscape that I had to declare a total removal program, which will take several years to complete. I remember this plant from my childhood when its peculiar herbal smell brought it to my attention. Its leaves are nearly round with a scalloped edge, and its stems are 8—18″ long, creeping along the ground 3—6″ high. The small flowers are not a very showy pale blue-violet. There is a variegated variety that may not be quite as dangerous. It reproduces both by copious seed and by root. Ground Ivy is a member of the mint family and it was used as a hops substitute in old times. This thug likes to hitch-hike along with another plant when gardeners share plants, which is how I got mine. It doesn’t look so bad at first, but my advice is “Don’t be merciful; eradicate it.”
Duchesnea indica or Mock Strawberry does look similar to a strawberry with its rosettes of three-lobed leaves, its runners, and its red fruits. However the flowers are yellow instead of white, the fruits are dry, spongy and insipid; and the runners gallop, quickly conquering any available ground. Years ago I made the mistake of recommending this bully as a groundcover. A year later, the woman called me to see her garden where Mock Strawberry had leap-frogged over half her new garden. She had to have it all removed ASAP, and I red-faced, learned not to recommend a plant I only knew from a catalogue.
One of the most notorious Flowering Bullies is Campanula rapunculoides or Creeping Bellflower, though most people know it as “Cancer of the Garden”. In summer this bellflower is seductive in its pretty, star-shaped, bell-like flowers of a violet or blue-violet color. They are arranged along one side of thin 2—4′ stalks. At the same time, below ground, the roots are running rampantly and rapaciously. Too often, kind gifts of plants from old neighborhoods contain root pieces of this uncontrollable tyrant. I was given a nice iris, only to discover a year later the flowers of this campanula blooming right next to it. Even though I recognized it, I was sure no campanula would survive long under my harsh, dry conditions: WRONG !! It suffered and dwindled and hid underground/ Until we had a wet year when I found/ It pushing up stems far and wide, so I vowed to give it no mercy whatsoever, forever.
One of the most common pretty weeds in old neighborhoods is Bouncing Bet or Soapwort. Saponaria officinalis was introduced from Europe as a garden plant. In colonial and pioneer days, the stems and roots were crushed in water to make soap (soapwort), and it was no doubt a renewable resource since it bounces back quickly from hard cutting or digging. Today in Colorado, it is a prohibited ornamental because of its invasive, bouncing character. Common Soapwort is a perennial, growing 18—30″ high on smooth, branching stems. It spreads by suckers and seeds. The flowers are phlox-like, five-petaled and borne in clusters at the ends of the stems. They are pink, blush or white, blooming in summer. It is drought tolerant and is often seen in large colonies when it blooms. Control it by preventing seeding and by clean cultivation. Please remove this plant if it has landed in your yard, because it is replacing native species in the wild, and because it is a bully in the garden.
Linaria vulgaris is Yellow Toad Flax or Butter and Eggs. It has been classified as a noxious weed because it has invaded our wild areas, but it is equally obnoxious in the garden. It is a pretty little demon. Its appearance is somewhat like snapdragon, growing 8—24″ high, with spikes of inch-long tubes of yellow with orange centers. Yellow Toad Flax can reproduce both by seed and by aggressive roots, and is adapted to both moist and dry soils.
I bought Linaria vulgaris about 15 years ago in my search for tough perennials, and by the second year, realized I had made a big mistake. Even under my dry conditions, it was spreading underground with considerable speed. I was determined to halt it and dug it thoroughly, flagging it to remind me to keep an eye on it. Each week I would watch for new shoots to emerge and as they came up, I would carefully dig them out. It still took me two years to finally be rid of it. This pretty bully is not to be invited to your garden party.
Not all bullies are as clearly undesirable as these seven. Many, like the herbs, are simply too strong spreading to be appropriate in a perennial garden or rock garden. Others that self-sow a lot can have a place if the gardener is willing to weed out the undesirable seedlings and leave a few in perfect spots. As long as an aggressive plant is not invasive in Nature, we might cultivate and test it. A bully in one person’s garden may be a valiant survivor in another’s, and a thug with moderate watering may be well-behaved under xeric conditions. So as gardeners in search of a balanced ecology, we must be watchful and wary of aggressive plants, ready to move or remove the bullies. And at the same time, we can love and cultivate those tough plants that can thrive in our often difficult Colorado conditions.
Other Aggressive Plants
Herbs that love to spread
1.Common Yarrow Achillea millefolium
2.Tansy Tanacetum vulgare
3.Costmary Tanacetum balsamita
4.Feverfew Tanacetum parthenium
5.Horseradish Armoracia rusticana
6.Comfrey Symphytum officinale
8.Chives/Garlic Chives Allium schoenaprasum/A. tuberosum
9.Horehound Marrubium vulgare
10.Lemon Balm Melissa officinalis
11.Clary Sage Salvia sclarea
13.Bedstraw, Cleavers Galium aparine
15.Natives to Watch Out for
Whiplash Daisy Erigeron flagellaris
16.Wreath Aster Aster ericoides
17.Golden Banner Thermopsis divaricarpa
18.Chokecherry Prunus virginiana
19.Wild Plum Prunus americana
20.Prairie Cord Grass Spartina pectinata
21.Sweet Grass Hierochloe odorata
22.Hops Humulus lupulus
23.Woods Rose Rosa woodsii
24.Silver Sage Artemisia ludoviciana
25.Trees to Be Careful of
26.Tree of Heaven Ailanthus altissima
27.Siberian Elm Ulmus pumila
28.Green Ash (female) Fraxinus pennsylvanica
29.Golden Rain Tree Koelreuteria paniculata
30.White Popular Populus alba
31.Black Locust Robinia pseudoacacia
32.Other plants that can be Bullies
33.Virginia Creeper Parthenocissua quinquefolia
36.Kentucky Bluegrass Poa pratensis
37.False Forget-Me-Not Brunnera macrophylla
38.Hawkweed Hieracium aurantiacum
39.Sweet Woodruff Galium odoratus
40.Creeping Jennie Lysimachia nummularia
41.Creeping Buttercup Ranunculus repens
42.Spring Cinquefoil Potentilla neumanniana
43.Periwinkle Vinca major/ Vinca minor