A grow bag is a type of container used in container gardening. Unlike rigid clay or plastic containers, a grow bag contains soil and nutrient in an enclosed plastic pouch. You can create a grow bag simply by cutting holes in a bag of pre-packaged potting soil. Or you can create your own grow bag by filling a plastic bag with soil. Like any other container garden, you can grow vegetables, such as runner beans, in a grow bag.
Select a grow bag that is large enough to accommodate the roots of a fully grown plant. Runner bean roots require 5 gallons of potting soil to thrive. You can purchase potting soil in 5 gallon containers and use it as an instant grow bag.
Perforate the bottom of the grow bag with an ice pick to create a series of small holes in the bottom of the bag. The holes should be large enough to allow for drainage, but small enough to not let soil out of the bag.
Elevate the bag by placing it on a rolling plant stand or two bricks to allow the bag to drain freely. Place the plant stand and grow bag near a trellis to support the bean plant as it climbs. Place the grow bag in a location where the runner beans will receive at least six hours of sunlight a day.
Cut a slit in the top of the bag to plant your runner bean seed. The opening should be just large enough to allow the bean vine to grow in diameter without constricting the plant's circulation.
Create a planting pocket by hollowing out the soil in the grow bag. Place the bean seed at twice the depth of the bean's width. Cover the bean seed with potting mix and water so that the grow bag is as damp as a wrung out sponge.
Check the grow bag daily to ensure that the soil remains damp as a wrung out sponge. Water the soil as needed.
Mulch over the top of the bag with hay or pine bark to help hold in moisture and disguise the appearance of the bag.