Controlling Invasive Plants – Durham Garden Forum Tuesday, December 11, 2018 6:30 – 8:00pm
Duke Gardens, 420 Anderson St, Durham, NC 27708
What are the invasive plants that threaten North Carolina and how can we control these plants? Learn which plants to avoid and prevent problems before they begin. If the horse has already left the barn in your garden, Johnny Randell, NC Botanical Gardens Director of Conservation Programs, will help you learn how to eradicate these thugs from your garden and landscape. Meet at the Doris Duke Center.
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$10 per meeting payable to Durham Garden Forum. Forum members free with $25 annual membership.
I have a lovely patch of chocolate chip ajuga—it has dark purple evergreen leaves and blue flowers in early spring. It spreads stoloniferously and lately, it has begun to drift through my perennial bed, establishing small colonies in attractive drifts. It’s a nice companion to red and yellow pansies in the spring, fades away to let perennials shine in the summer, and provides a fluffy green and purple texture to brighten winter.
So, just imagine my horror this summer, when hundreds—I kid you not—hundreds of tiny, bright green weeds appeared woven throughout my ajuga like a rampant cancer.
There was nothing to be done but spend hours on my hands and knees painstakingly plucking the little suckers out one by one. I discovered the name of my new weed is chamberbitter, which sounded exotic enough to make me feel a little better. It looks a little like a mimosa and has yellow flowers under the leaves. It likely rode in on something I planted, or perhaps one of the many birds I feed graced me with it. I must have missed it last year, and it set seed and multiplied. It is now July, and I am still plucking at it, watering it with my sweat as I go.
This awful experience got me thinking about the strategies weeds use to get into our gardens, gain a foothold, and multiply. They have multiple methods of getting into our gardens—through birds’ digestive systems, in containers from nurseries, or they simply ride in on the wind! One source I consulted suggested removing the top layer of soil from nursery plant containers before planting. This seems like a good strategy, especially for the ubiquitous oxalis! But I can’t think of anything to stop the weed attack from birds or the air…
As happened with my ajuga, weeds like to mingle with existing plants—nestled as close to our favorite plants as possible. This provides protection and makes them harder to eradicate. They also are adept at snapping off when we try to pull them, leaving their roots intact to sprout again. For bigger weeds, I use a Japanese hori hori knife.
The knife can slice into the dirt just at the base of the weed, without disturbing the soil too much. Then you can grab it as close to the ground as possible and pull. Other valuable tools include an old table fork for twisting out the roots of weeds and a fishtail weeder for digging out tap-rooted or bulbous weeds such as dandelion, violets, or dock.
This may come as a shock, but every inch of your garden and mine is chock full of weed seeds. They can lie dormant for years, and all they need to germinate is a little light. When we dig, plant, or even hand weed, we bring weed seeds into the light. So, it’s critical to cover any exposed or disturbed soil with mulch. Two inches of mulch is recommended. More can cut off oxygen to the plants we love. Never skimp on mulch—I would skimp on fertilizer before I skimped on mulch!
The best time to pull weeds is before they set seed, and after a good soaking rain. Once weeds set seed, the battle is lost. You’ll be fighting them for years to come. After a rain, weeds come up easier with less disruption of the soil, and mulch applied after weeding will hold in the moisture from the rain. For really bad weed infestations, the best solution is spraying with glyphosate. But this is not an option in closely planted landscape beds, as glyphosate kills any plant it comes into contact with.
Never put freshly pulled weeds into the compost bin. Heat is the key to composting them. I find it very satisfying to lay them out on my asphalt driveway where I can watch them cook in the sun. Even after they are fully cooked, I’m not brave enough to put them in my compost bin, but sources say, once they are dead and rotting, you can put them in clear plastic bags, leave them in the sun for two or three days, then compost them. (I don’t now that I reallyneed compost all that much!)
We are all busy. It would be great if we could mulch at the best time and weed at the best time. But sooner or later, we all miss the ideal timing. I think weeds know this will happen, and they take full advantage of it. By nature, they are designed to grow and set seed rapidly, the better to evade the gardener and spread their offspring across the land. So, if you can’t get in to fully eradicate them, lop off their heads. This keeps them from setting seed until you can get back in the garden.
I am not sure I believe this, but according to soil scientists, fewer weed seeds germinate in soil that contains lots of compost and organic matter. But it can never hurt to enrich the soil, so good advice regardless! (My perennial bed is full of compost and organic matter, and I have plenty of weeds…just saying …)
My goal every year is to get everything planted, weeded, and mulched before we leave for the July 4th holiday. Then I coast until time to plant winter veggies in early August. I wish everyone a weed-free summer!
So here is a rogues list of plants I have been fighting lately. Only because of its name, tops on my list is Hairy Crab Weed, or Mulberry weed. It is a monstrous weed and it has a distinct smell.
Then of course there is Japanese stilt grass, which is ruining the chances of survival for our native wildflowers. It loves shady woodland environments.
Nutsedge is another candidate for most obnoxious! The best weapon for this one is glyphosate but if it’s in your perennial bed, that’s not an option since the spray will kill your desirable plants. Nutsedge retains a “nut” or a seed, in the ground. After you pull it, it will re-sprout.
So, I guess the bottom line is, weeds are just something we are going to have to deal with. I don’t think you can completely eliminate them but if you set aside a day each month to pull them, you can keep them somewhat at bay. Happy Summer!
Bittercress (Cardamine hirsuta), also known as lamb’s cress, spring cress, wood cress, or flickweed is a member of the mustard family Brassicaceae. It is a winter annual, but can persist year-round in a moist, shaded environment in disturbed areas.
I find it throughout my garden primarily in and along the gravel paths (where I might have tracked it’s seed over the years), and in the moist corners of some garden beds. It also loves my currently dormant raised veggie bed. Since I must garden in high shade conditions on our wooded lot, I have the perfect environment for it. It also loves container pots, so be sure to pull every last little seedling out of plants that you bring home from the nursery.
This pesky menace is native to Europe and western Asia but was introduced and naturalized throughout much of the US and the world. *
As it grows, it demonstrates an upright growth habit with a dense basal rosette. The shoots bearing its tiny white flowers grow up from the center from 3 to 8 inches high. Pull these little devils up by the roots before the seedpods form. When mature, the pod splits open and forcibly expels the sticky seeds up to 6 feet! One plant can produce 5,000 seeds that can germinate quickly or remain viable in the soil for many years. Hence the clusters that occur. In the gravel paths a scuffle hoe can cut them down, but it is best to pull by hand and get the root. I prefer to garden chemical-free, but I may have to seriously consider a pre-emergent weed treatment in the future.
*From ENH1250, one of a series of Environmental Horticulture Department, UF/IFAS Extension. Original publication date December 2014. http://edis.ifas.ufl.edu/ep511.