Question:
How do I get rid of the yellow flowering weed called Oxalis without damaging my Lantana plants? I've come to dislike it after spending hours cultivating them out each year only to have them return.
Answer:
The yellow flowering Oxalis is a broadleaf weed called Creeping Woodsorrel. The foliage may be green or a maroon red color. It belongs to a genus of plants that has many desirable varieties such as the the four-leaf clover associated with St. Patricks Day. It’s a common problem in turf, containers and in the landscape. Oxalis is difficult to control but with some patience, you should be able to rid the Lantana plants of the Oxalis. It will will require a two part strategy. Oxalis reproduces itself by spreading quickly from the actively growing plants and from the seed produced from the yellow flowers. Thus, cultivating alone doesn’t solve the problem as the seed geminate to continue the headache. Seeds are very small blending into the soil and/or blown into the surrounding areas. The seeds are the primary reason or source for the increased frustration gardeners have in controlling this problem. While we can control Oxalis in turf with herbicides, they are harmful around ornamentals, thus we we have no selective chemical controls for the actively growing Oxalis plants around desirable plants. You’ll have to cultivate the area by hand and or spot treat it with Round Up or similar herbicide. Round Up is a non selective herbicide that is absorbed by the leaves and not the roots. You protect the desirable plants by using a cardboard plant shield. The plant shield prevents the desirable foliage from being sprayed and removed or moved as you spray an area. You’re now able to spray farther under the canopy of the Lantana plants and hand weed rest of the area. With containers you’ll have to hand weed. Next apply a pre-emergent herbicides to control the dormant seeds. A pre-emergent herbicides will not harm any plant that has roots and is applied right after cultivating an area. For landscape areas, I’d apply Monterey Impede and spray it right over the desirable plants. It’s a liquid and best applied with a tank spray. Three ounces of the concentrate is evenly sprayed over designated area in any amount of water. The area is then irrigated afterwards to set up the chemical barrier. One application should last six to eight months or any time you disturb the barrier. Light cultivation down to one inch shouldn’t disturb the barrier. For smaller areas and containers. I’d use a granular, Bonide Crabgrass Preventer and sprinkled over the area and watered into the soil. It can also be applied over a larger area in a hand held spreader. I should also mention it’s very probable that some of the Oxalis will return from the roots that remain in the ground. Again this is a war of attrition that you should win.
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