The short answer
Not always — it depends on your plants. Rhizome and water-column feeders (Anubias, Java fern, mosses, most stems) grow fine in plain gravel or sand because they don’t feed through the substrate. Heavy root feeders and carpets do far better in a nutrient-rich aqua soil, though gravel plus root tabs is a workable budget alternative.
When gravel is fine
If your plants attach to hardscape or draw food from the water, the substrate is just an anchor. Java fern, Anubias and mosses tie to wood and rock and don’t touch the substrate. Rooted stems and swords will grow in inert gravel too — you simply add root tabs to feed their roots. See the aqua soil vs gravel comparison.
When aqua soil earns its place
An active aqua soil stores nutrients, releases them to roots, and gently softens and acidifies the water — conditions many plants and shrimp love. It’s the standard base for carpets and demanding root feeders, because it feeds them from below right where they need it. If you’re aiming for a lush, plant-heavy scape, soil is worth it — see our planted substrate picks, best aqua soil and the substrate hub.
Match substrate to your plan
Choose the substrate around the tank you want. Going low-tech with easy plants? Gravel or sand plus root tabs is plenty. Building a proper aquascape with carpets and root feeders? Start with aqua soil. Either way, feed the water column with a good all-in-one fertiliser, and see how to plant aquarium plants for getting them in cleanly.