Super Sprouter? 10 in x 20 in tray is built to the Industry Standard size and thickness. Great for propagating your seedlings with rock wool, seedling mix or starter plugs. Super Sprouter? trays come without holes so that the tray can catch excess water to keep starts or plants moist. They are also available with holes so that the tray can be used in a flood and drain method. Raised channels are incorporated in the base of the tray to provide air to circulate under your pot or insert tray.