Flushing Outdoor Plant?

hey,
how do u flush a outdoor plant that is in the ground, in good soil, with a layer of plastic to keep away from natural soil....

I'm assuming the plastic in the ground has holes in it for drainage?The last couple weeks just water with straight water(no nutes).The amount of water you use to flush is up to you

yes the plastic has holes in it... i was a bit worried that i might drowned it when the weather gets worse.. i was thinking bout just feeding it molasses and potash the last 2 months that would b ok 2 ??