6L Plastic Planting Bags These are the bags we use.. Description Black Plant Bags can be used to ‘plant-up’ seedlings to give them more growing room before transplanting, or to give you a place to put growing seedlings that don’t have bed space yet. Black plant bags are used as a cheap alternative to pots and in cases where the grower is planting large volume of plants like the ones that you would see in nursery environments. Also used as a cheap alternative for different transplant stages before they go into final pots or beds. The bags have drainage holes on the side of the bags, creating a slight water build up in the bottom for extra thirsty plants.