What is an indoor hydroponic gardening system? Indoor hydroponic gardening systems are methods by which plants can be groomed without the need for soil.indoor gardening Instead of using soil, indoor hydroponic gardening systems use nutrient solutions instead. This nutrient system is fed to the plants directly and avoids the need for other plants to compete with the scarce nutrients in soil. Hydroponic gardening systems can be a great way to grow plants. They take up relatively little space and can be used in a clean environmentally friendly way. With most hydroponic gardening systems, your plants will grow quicker and be more healthy. They take the nutrients directly from the solution.