underplant

under- +‎ plant

underplant (third-person singular simple present underplants, present participle underplanting, simple past and past participle underplanted)

1. (transitive) To plant underneath.
   • 2007 August 23, Charles Elliott, “Organic Looks Easy, if You’ve Got a Royal Staff”, in New York Times‎:

     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.

underplant (plural underplants)

1. A plant that has been planted underneath others.

• Puntlander