Dollar weed (Hydrocotyle spp.), also called pennywort, is a spreading, low weed found in lawns and groundcovers that grow in bright light and wet soils. An easy way to diminish dollar weed is by reducing irrigation drastically. Less watering coupled with an application of a broadleaf herbicide can knock back dollar weed so that the Asian jasmine (Trachelospermum asiaticum) can grow more robustly and choke out or shade remnant weeds.
Reduce irrigation to the bed of Asian jasmine that is infested with dollar weed. Asian jasmine grows in soil that is slightly moist to occasionally dry, whereas dollar weed prospers and is bothersome when soil is moist to wet and soggy.
Hand-pull clumps or running stems of dollar weed that remain after the soil dries and a new irrigation schedule is created. Little by little the pulling of weed stems from the jasmine can eliminate the problem, especially if the soil moisture is not favoring the proliferation of more dollar weed.
Consider an application of a broadleaf herbicide, like Roundup, if steps 1 and 2 prove unsatisfactory. Roundup is made of the chemical glyphosate, a nonselective herbicide that will affect any and all plants that it comes in contact with.
Mix a 1/2 to 3/4 strength dosage of glyphosate-based herbicide into a spray bottle or backpack sprayer. Follow product label directions and recommendations, but simply modify the dosage of chemical to create the 1/2 to 3/4 solution. For example, if full strength dosage is 1 teaspoon of product per gallon of water, reduce the amount to no less than 1/2 teaspoon of product.
Spray the solution evenly onto only the foliage of the dollar weeds, not onto the foliage of the jasmine. Some spray-drift is expected, but don't douse the jasmine foliage if possible. Any part of a dollar weed plant that is sprayed will transport the chemical to all of the plant by the vascular tissues.
Watch the glyphosate-treated area for the next three to 10 days. Look for wilting or yellowing dollar weeds, which is a sign the herbicide is working. Also note if the Asian jasmine is yellowing, a sign the dosage of chemical may have been too potent.
Repeat steps 2 through 6 if the initial application of herbicide did not fully kill the dollar weeds.