You can make the simplest grow bag from an unopened bag of topsoil. Like all other varieties of container gardening, tending grow bags is not hard and should lead to a decent vegetable crop if you follow some basic rules. If you have poor soil or limited gardening space, grow bags are an especially attractive option, but they are also an educational project for children.
Lay a bag of topsoil flat in a location that receives at least six hours of sunlight per day. Place at least a 2-inch layer of sand or fine gravel on the ground under the bag. This promotes drainage, and then you won't have to worry about excess water seeping out where you don't want it. The University of Missouri, which conducted grow-bag trials in 2008, recommends cutting about 10 slits on one side of the bag, about 1 inch each, for drainage.
Carefully turn the bag over so little or no soil falls out the slits. Then place 2½-inch X-shaped cuts in the bag for planting vegetable seedlings. The number of cuts is determined by the vegetables you want to grow. Cut two Xs if you want to plant tomatoes, four for peppers, cucumbers or summer squash, and six or seven for planting green beans, for example.
Plant the seedlings, one per hole, in the bag. Push them into the holes gently after moving some of the soil to one side. Make sure the roots are properly covered.
Mix 2 cups of fertilizer into a gallon of warm water. Stir well to dissolve the fertilizer completely. This is your base fertilizer solution.
Add 2 tbsp. of the base fertilizer solution to 1 gallon of water. Use this nutrient solution to water the vegetable plants daily, or as needed. Pour the nutrient solution slowly, some into each hole. Stop when it begins to seep out the bottom through the drainage holes.
Leach excess nutrients from the grow bag once a week by watering them with plain tap water. Add water until it flows freely out the bottom drainage holes.