underplant

verb

1. (transitive)To plant underneath.

   “Such small, exquisite enclosures as the Sundial Garden beside the house, planted by Mr. Howard with near-black and white perennials chosen to bloom sequentially for 10 months of the year, or the Azalea Walk, with its underplanting of bulbs and season-extending clematis, cannot take care of themselves.”

2. (transitive)To plant too little of.

noun

1. A plant that has been planted underneath others.