Q: In the flower bed in our front yard, we pulled all the weeds out, put down some landscape fabric and then put down some bark. But the weeds have returned, coming up through the landscape fabric and the bark. I would like to use a chemical weed killer like Roundup to get rid of the weeds. Will this ruin the soil underneath if I want to plant flowers after the weeds die?
A: The manufacturers of Roundup, which is the most widely used herbicide in the world, have long claimed that their famous weed killer does not damage soil and has no effect on subsequent plantings. No one has proven otherwise, and you should feel confident that application of Roundup will not impact growth of flowers in the sprayed area.
One of the most fascinating recent developments in agriculture involves genetic engineering of Roundup Ready crops, which have a gene that confers Roundup resistance. Much of the soybeans, corn and cotton grown in this country is Roundup Ready, which means that, should the crops become choked with weeds, Roundup can be sprayed on them directly. The surrounding weeds will die even as the crops continue to grow without any signs of ill health. Roundup Ready crops due for release in the near future include lettuce, potatoes and alfalfa.
The problem with widespread use of Roundup, or any pesticide for that matter, is the potential for development of resistant weed species. This has already happened with annual ryegrass in California almond orchards. Certain strains of annual ryegrass are no longer killed by Roundup.
Plant scientists have developed Roundup Ready creeping bentgrass, which is used on putting greens throughout the United States. Presently, a Roundup Ready tall fescue is also being engineered. Tall fescue is the most popular lawn grass in Los Angeles and is sold under brand names such as Marathon, Bonsai and Medallion. With a Roundup Ready lawn, you could spray Roundup over every square inch of it with assurance that only weeds would be killed.
The reservation expressed over release of Roundup Ready grasses concerns the possibility that their seeds would be dispersed and give birth to generations of Roundup-resistant plants. In other words, if Roundup-resistant creeping bentgrass or tall fescue got into other types of lawns, or into fields of Roundup-resistant crops, the problem of chemical weed control would have come full circle, and another herbicide would have to be found to control the bio-engineered grasses.
Through a few prudent actions, you can minimize the burden of weed control in your lawn and garden. For the most part, entry of weeds into your property is under your control. For example, make sure you procure your plants from a reputable nursery. Plants originating in wholesale yards, including many planted by your gardener, often have weeds or weed seeds in their soil. If, at the nursery, the name of a large grower such as Monrovia or Hines is attached to the container, you can be confident that the soil will be weed-free because of the quality control maintained.
Where lawns are concerned, a primary source of weeds is the gardener’s mower. If you see dandelions or crabgrass growing in your lawn, chances are you will see these weeds in all the lawns your gardener maintains. Weed seeds stick to the underside of a lawn mower and are easily spread around as the machine moves from one yard to the next. Neighbors are another source of weeds. If you live across the street from someone with a weedy front lawn, chances are good that your front lawn will eventually end up in a similar condition. It makes no sense to spray your weeds if you do not spray your neighbor’s as well.
The only weeds beyond your control are those whose seeds are brought onto your property by birds, squirrels and other wildlife.