Soil and Fertilizer: You can use soil in your container vegetable garden, but the synthetic mixes are much better. Peat-based mixes, containing peat, perlite or vermiculite, are excellent. They are relatively sterile and pH adjusted. They also allow the plants to get enough air and water. However, I like to mix in 1/3 part compost planting mix which improves fertility, 1/3 part peat, and 1/3 part perlite. I also mix in a slow release 6-6-6 fertilizer which keeps vegetables feed for most of the growing season.