Biome spread
The world bleeds with three living colors that refuse to stay still
The evil biomes and the Hallow , unlike all other biomes, can spread to other areas of a world. They slowly convert, or "infect", certain tiles which are near their own biome-exclusive tiles to their respective biome counterparts, increasing the size of the biome. The exact rules for biome spread are slightly different for each of the three infectious biomes, as described in depth below. Collectively, these three biomes can be called the "infectious biomes". Blocks and walls which are vulnerable to infection are called "corruptible", and those which cannot be infected under any circumstances are "non-corruptible". Blocks and walls which could be infected, but have not been, are called "pure". Biome spread starts immediately after world generation. It is greatly enhanced and sped up upon initiating Hardmode (once the Wall of Flesh has been defeated for the first time), leaving few restrictions on the spread of the infectious biomes for the rest of the game. Defeating Plantera for the first time slows biome spread down somewhat again. The biome spread process is part of the game's "tile update cycle": Every game tick, the game chooses a handful of tiles to update, which covers several processes including biome spread. The tiles above and below the surface level are selected in separate passes; as an approximation, "surface" tiles will each average about one update every 140 seconds, while "underground" tiles each average about one update every 830 seconds. (That is, above-ground tiles get updated about six times as often as below-ground tiles, so biome spread will be that much faster above ground.) Due to the random selection method, even the averages here are approximate, and the actual length of time between a given tile's updates can vary wildly. When an infected tile
Lore & Background
In the silent depths of creation, a subtle war wages not between armies, but between the very soil and stone itself. The Corruption, the Crimson, and the Hallow are not merely regions; they are sentient plagues of color that hunger for purity. From the moment the world wakes, these infectious biomes begin their slow, inexorable march, whispering to adjacent tiles until the earth shudders and changes its skin. Above ground, where the sun kisses the dirt, this transformation happens with frantic haste, while deep below, the infection creeps like a shadow in a dream, patient but inevitable.
The balance of power shifts dramatically when the Wall of Flesh falls, unleashing Hardmode with a violent surge that strips away all previous restraints. The green grass turns to violet rot or blood-red thorns, and the Hallow spreads its crystalline light to cleanse the darkness, only to become a new tyranny in its own right. Yet, hope remains in the form of the Plantera's defeat, which acts as a dampening force, slowing the frantic pace of this eternal conflict to a manageable crawl, allowing the world to breathe once more before the final confrontation.
Even the humble sunflower stands as a lone sentinel against this tide, its golden face casting a protective field that no evil or holy grass can cross. It is a fragile barrier in a world where the ground itself seeks to consume you, reminding travelers that while nature may be wild and mutable, there are still places where purity can hold firm against the encroaching chaos.
In Their Own Story
You stand at the edge of the forest, the air thick with the scent of ozone and rot. To your left, the vibrant green grass has already surrendered to a patch of sickly purple Corruption, its vines twitching like living veins. You watch in horror as a single block of dirt nearby shudders and transforms into mud, then instantly twists into a crimson thorny bush, the change rippling outward faster than the eye can follow. The ground feels wrong beneath your boots, humming with a malevolent energy that seems to breathe.
Desperate, you plant a row of sunflowers along the border, their bright yellow faces turning toward the sky in defiant silence. For a moment, the advance halts; the purple grass hesitates at the edge of their protective aura, unable to cross the invisible line they cast. But then, deep underground, a distant rumble vibrates through your soles. The infection is not just above; it is seeping up from the caverns below, bypassing your defenses entirely. You realize too late that while you fought the visible tide, the true enemy was already rewriting the world beneath your feet, turning the very bedrock into a weapon against you.
Reader's Guide
Biome spread is the game's dynamic system where Corruption, Crimson, and Hallow convert nearby pure tiles to expand their territory. This process begins instantly upon world creation but accelerates violently after defeating the Wall of Flesh to start Hardmode. Understanding this mechanic is vital for progression, as unchecked spread can turn your base into an enemy zone, spawning hostile mobs and altering resource availability.
In Pre-Hardmode, spread is limited strictly to grass and thorny bushes converting adjacent blocks. Once Hardmode begins, a 7x7 square area around any spreading tile becomes vulnerable, allowing evil and Hallowed biomes to convert stone, sand, ice, and more. Note that while wild Crimson plants can act as sources, their Corruption counterparts cannot; this asymmetry is unique to the game's logic.
To manage spread, utilize Sunflowers which block conversion within a 2-tile radius on all sides except the two blocks directly beneath them. Defeating Plantera is the single most effective late-game measure, reducing the spread speed by 50%. Remember that wall updates occur roughly six times faster above ground than underground, meaning your surface defenses require constant vigilance while deep caverns change more slowly but are harder to monitor.
Did You Know?
- Sunflowers block all conversions within a 6x8 tile margin around them, except for direct grass spread on adjacent blocks.
- In Pre-Hardmode, only grass and thorny bushes can spread biomes; in Hardmode, almost any corruptible block can convert neighbors.
- Defeating Plantera reduces the biome spread speed to exactly 50% of its default Hardmode rate.
- Wild Crimson plants can act as source tiles for infection, but their Corruption equivalents cannot.