Purchase side-planting coco liners for your 20" diameter x 11" deep double basket planter.  The coco liner for this deep planter has 21 pre-cut holes for an instant, full effect for your side-planting baskets.  The large liner can hold 21 side plants, 14 top-edging plants, and three (3) 6" or gallon size centerpiece.  Use plants from  3" or 4 1/2" pots for the side plantings. 
 
We also have liners without holes to fit these planters.