If you are a gardener, you certainly don’t need an introduction to weeds. They can be a nuisance and detract from the overall appearance of the garden, but more importantly, they can rob the soil of precious water and nutrients. Especially in our Mediterranean climate and the ever-increasing cost of water, you don’t want to be giving it away.
Weeds, simply put, are plants growing where they aren’t wanted. You generally think of weeds being those pesky things growing around the base of your roses, but based on the general definition, even roses, under the right conditions, can be considered weeds. They come in a myriad of shapes, colors, sizes, and degrees of tenacity…some are pretty easy to control, while some, like bindweed (or what I consider the Kudzu vine of the west) seem to withstand and almost thrive on significant abuse. Most common weeds that plague rose gardens include annual types of crabgrass, mallows, purslane and spotted surge, and perennial types of bindweed, dandelions, nutsedge and oxalis.
Methods of controlling weeds can include preventive methods and removal methods. Prevention generally focuses on some type of weed suppression. Indirect methods of weed suppression include garden design, habitat modification or horticultural controls. A garden area designed with no water or soil would eliminate the elements necessary for the plant to grow (driveways, paths, patios), while modifying a habitat by reducing the available water and sunlight, making life difficult for weeds to germinate and sustain growth. You can reduce available water by using drip irrigation to put water only where it is needed, and reduce sunlight by adding mulch. Mulch can take the form of anything from bark, landscape fabric and newspapers to compost, gravel or wood chips. Horticultural controls utilize crowding of plants to reduce the available space for them to grow, and can also include planting certain types of plants that have some level of inhibition for seed germination.
You can use preemergents that actually inhibit the germination of seeds (any seeds, not just weed seeds). Suppressa, a natural herbicide, is made from corn gluten meal and also provides some nutrients to the soil. Chemical products such as Preen, can be broadcast to the top surface of soil and will inhibit weeds for up to a season with one application.
If you already have weeds, then you can choose a physical method of removing weeds, or use a post emergence chemical herbicide. Physical controls include manual removal – good old hand pulling weeds or hoeing. A really good tool for weeding is a “hula hoe”; you push and pull this hoe that gets under the roots and loosens the weeds for speedy removal.
Heat is also an effective erradicant. One very effective method, especially when planting a new bed, is through solarization. Put some black plastic over the planting area for a week or two during warm weather and it will heat the soil and destroy the weed seeds. Another use of heat is with flamers - portable gas torches that produce intense heat (about 2,000° F). When you pass the flame over and around weeds, it quickly boils the water in the plants' cells, causing them to burst. Once the heat destroys any section of a weed's stem, for instance, water and nutrients cannot reach the leaves, and the top part of the weed dies. The manufacturer claims that killing weeds is as easy as holding the flamer and walking slowly between garden rows. Killing a weed requires heat for only 1/10 of a second. While it is supposed to be pretty easy to use, take caution if using around any flammable materials.
Chemical postemergent herbicides like sethoxydim (Grass Getter), fluazifop (Fusilade II & Ornamec) and Rosmania’s organic fatty acid (Scythe) can safely be used in your rose garden for controlling most actively growing weed grasses without damaging your roses. Many hard to kill broadleaf weeds such as oxalis can be controlled with effective broadleaf herbicides, however they must be used with extreme caution. Roses are extraordinarily sensitive to broad-leaf weed killers and even the slightest amount of drift can cause stunted, twisted, cupped, curled, chlorotic foliage and even death to your plants. Damage from the popular non-selective herbicide glyphosate (Roundup) is commonly mistaken for disease or insect damage on roses. Be aware that damage from Roundup can occur the following season if fall applications are made near your roses and accidentally drifted on the susceptible green stems. You need to be extremely careful when using these types of products, since they are non-selective and will kill any green plant they contact.
Photo by Jillian Pond used with permission from: iStockphoto