This is not the dreaded aggressively invasive Saint John’s wort that has naturalized in other regions. Nonetheless, creeping Saint John’s wort, Hypericum calycinum, does precisely as the name implies. It creeps, and has naturalized to a less aggressive degree in many spots near the coast. Its vigor is an advantage to many landscapes, but might eventually displease adjacent neighbors.
Creeping Saint John’s wort is a somewhat rustic perennial ground cover that does not need much water once established. It naturalizes in coastal climates because it gets all the water it needs from annual rainfall there. Although evergreen, it looks best if mown as winter ends. It happens to be susceptible to rust, and mowing removes much of the old foliage the the fungus overwinters in.
One to two inch wide bright yellow flowers, with five petals and prominent stamens, start to bloom in June and continue into September. By that time, the paired leaves might be getting tired if not watered, or infested with rust, but should stay presentable until mowing at the end of winter. Crowded plants might get three feet high. Otherwise, growth does not get much more than a foot deep.