Then dig out the oxalis or kill it with Roundup, Finale or similar product that permits replanting. Control should be obtained in two to three weeks. When the oxalis turns brown, remove the debris and then till the soil deeply to prepare a new bed for the day lilies. The saved plants can be quickly reestablished in time for spring blooms. We have a large above-ground planter to fill with soil and plants.
Most products blended for container plantings available at garden centers are fine.
Avoid mixtures with white polystyrene portions that are light and can be blown into the pool water. Make sure the planter has good drainage. You might add a few inches of coarse gravel to the bottom of the container. This prevents soil from plugging the drainage holes. Annual or perennial flowers for spring through summer include ageratum, blue daze, celosia, crossandra, gerbera daisy, marigold, pentas, snapdragon, torenia and wax begonia.