CONTROLLING WEEDS
IN
TENNESSEE ROSE GARDENS
by Roger Bryan

Jeff usually asks me to write something about getting rid of bugs or fungus in our rose gardens. However, for a change of pace, this time we’re going to look into getting rid of weeds. I’ll start by identifying the most prevalent weeds that typically grace our Tennessee gardens and lawns. Then I’ll take a look at four ways of eliminating or, at least, reducing the magnitude of the weeds’ encroachment.

Our Favorite Weeds. - It doesn’t take much time, doing research on the Internet, to discover that weeds are really a serious problem for farmers and gardeners around the world. A classic example in the South is kudzu which, left uncontrolled, would quickly “devour” everything in its path – fortunately, it hasn’t yet moved into our gardens. A weed that does invade our gardens is creeping spurge, a perennial (that’s right, it comes back year after year) broadleaf weed with spreading, prostrate stems that exude a sticky, milky sap when broken. Another favorite of mine is hairy bittercress – it’s an annual that especially likes to grow in the containers holding my miniature roses, and when I go to pull it out it shoots its seeds as though from little cannons, so I immediately know it’ll be back soon. And everyone’s familiar with smooth crabgrass, a summer annual that can quickly spread throughout your garden. Another pesky weed that shows up in my garden is yellow oxalis – a perennial that looks a lot like clover but has a little yellow flower. Last but not least is small-flower galinsoga – this annual weed is always lurking at the edge of my garden waiting to take over. Pictures of all these weeds are available by typing its name into the Internet search engine, Google – some of the pictures are scary like the one for galinsoga showing it completely “drowning” a farmer’s pepper crop, and he can’t do anything about it – can’t till it under without destroying his pepper plants and can’t use an herbicide.

What to Do? – One excellent answer to this question can be found on the Rose Society’s website, www.chattanoogarose.org (click on Herbicides on the website’s homepage) in a slide show created by Ron Strahan of the LSU AgCenter. The focus of Ron’s presentation is upon the use of herbicides – in the paragraphs that follow, we’ll take a look at four methods of weed control, including the use of herbicides.

Pull‘em up. –Otherwise referred to as weeding. This is a tedious method of ridding your garden of weeds but it’s often the most expedient and effective method. Creeping spurge, for example, is easy to pull because it grows into a large spreading weed with only a single flimsy root at its center. Crabgrass and yellow oxalis, on the other hand, put down pretty tenacious roots that are difficult to dislodge without leaving some of the weed in the ground to re-grow. In any event, a couple of hours of weeding will usually make your garden look nicer – at least for a couple of weeks until the weeds return.

Cover‘em up. – A number of companies (e.g., www.preen.com) produce landscape fabric that can be used to cover large areas of your garden and thereby prevent weeds from growing up through it. Typically landscape fabric costs about 6¢ a square foot. But who wants a garden covered in fabric? So you cover the fabric with mulch to hide it and what happens: the weeds start growing in the mulch. Moreover, in an established garden the fabric is difficult to place around existing plants/bushes. My points are: (1) landscape fabric is effective only when it’s covered with something that won’t support the growth of weeds – for example, pea gravel to create a garden pathway, and (2) fabric is practical for new gardens but difficult to tailor to existing gardens. [It is h and y, though, to use as a liner in the bottom of pots/containers – it lets water run out without the loss of potting soil through the container’s drain holes.]

Get ‘em before they start growing. – Here’s where pre-emergent herbicides like Preen play a role. Typically, the active ingredient in pre-emergent herbicides is trifluralin, a chemical that inhibits seeds from developing roots. An obvious application for me is in my miniature rose containers just after I pull out all the hairy bittercress which, in turn has cast its seeds throughout the container -- I sprinkle in some Preen granules, water them in, and the bittercress seeds never take root.

Preen also makes mulch impregnated with trifluralin that can be spread over landscape fabric to form a pretty effective barrier to weeds. However, the treated mulch (which comes in several different colors) costs about $2.50 a cubic foot making it a bit expensive for any but the smallest gardens. Preen is not the only pre-emergent herbicide available to gardeners – there’s Ronstar by Bayer, Pendulum by BASF, Barricade and Princep (liquid) by Syngenta, and Treflan by Dow. Preen, however, is probably the most readily available through outlets like Home Depot and Lowe’s.

Kill’em. – Now we’re talking non-selective herbicides like Roundup. Roundup has gained a bad reputation primarily from those who weren’t careful in its use. Roundup is very effective and will kill almost any plant to which it is applied – weed or not. The active ingredient in Roundup is glyphosate which inhibits the production of a particular enzyme in plants that is needed for them to remain alive. Roundup should be applied to the foliage of the plant/weed to be eliminated. From the foliage it moves systemically through the plant eventually killing it and its roots.

Monsanto originated the glyphosate-based herbicides but patents have lapsed and Roundup-generics are now available from a number of suppliers such as Scott (www.scotts.com/roundup). Monsanto has, however, created some genetically modified crops like alfalfa, corn and soybeans which are termed “Roundup-Ready” meaning they can be sprayed with Roundup without effect while the surrounding weeds are killed. Roses, though, are not Roundup-Ready and great care must be taken in applying Roundup in your rose gardens.

I suggest that Roundup never be broadcast sprayed in or around rose gardens – there’s always the chance of overspray landing on the bushes. What I do suggest is the use of Scott’s Roundup Ready-to-Use PLUS in the 1.33 gallon refillable Pump’N Go Sprayer. The spray wand should be set to the narrowest stream possible so weeds can be precisely targeted. I wouldn’t spray closer than, say, a foot from the base of a bush and would take great care not to get any spray on the bush. Spray that hits the soil (or is washed off by rain that occurs within 30 minutes of the time it is applied – before it is fully absorbed by the weed) is rendered harmless because glyphosate binds tightly to most types of soil and therefore won’t migrate from the point of application. Furthermore, the enzyme blocked by glyphosate is not present in humans or other animals so there’s low risk to human health if Roundup is used sensibly according to label instructions.

My Choice. – I have an established rose garden of about 120 bushes with about 30 miniature roses in containers. For me, the most effective approach to the elimination (or more accurately, reduction) of weeds in my garden is: (1) putting down, every year, garden fabric over the large areas where nothing is to be planted or where containers will be placed, then mulching (just regular mulch) over the fabric, and finally spreading Preen over the mulch; (2) weeding the containers with the minis and then applying Preen; (3) hand weeding close in and around the in-ground bushes; and (4) using Roundup on any weeds that pop up in the open areas away from the bases of the bushes – usually, in my case, creeping spurge, smooth crabgrass, and yellow oxalis. The small flower galinsoga I mentioned earlier doesn’t usually encroach in the rose beds – it usually shows up in other plantings and I let it go (it’s not unattractive) until it starts to flower – then I put on the gloves and rip it out by the handfuls.

As with any pesticide, please Read the Labels on any of the herbicides you use.