How big do artificial biomes need to be to spawn monsters?

I'm building my artificial biomes in Terraria so I can farm certain things and have enemies spawn. The question is how big do the biomes need to be?

So far I've built a crimson, underground jungle, surface jungle and a desert but none of them are spawning monsters. I've read the Guide on Artificial biomes on Terraria wiki and many other forms but I have not found my answer. Can someone please give me detailed information?

I have enough blocks to where the background and music changes for each biome and yet still no monsters.

7 Answers

The Terraria wiki does have an answer on how big many of these biomes have to be:

For example, snow biome requires 300 snow blocks, ice blocks, or snow bricks.

Generally, you'll want to keep adding blocks until the background changes.

You can also try a Water Candle to increase monster spawn rate.

11

Monsters only spawn in a certain distance in tiles from the player i.e. between 62 - 84 blocks to the left or right of the player and between 35 - 47 up and down. Its not enough that the biome has to be off screen but it has to be in between these distances. So either make the biomes bigger i.e. 168 * 94 blocks with the player in the centre or dig out the middle and have the edges the biome you want.

I can't even get the background or music to change. But that didn't worry me and it shouldn't worry you because to my surprise in my artificial snow biome failure a zombie eskimo spawned.
Basically it doesn't matter what size the biome is, mobs will still spawn just slower. However the bigger it is the more it will spawn monsters.
Hope this helped.

Review the Terraria Wiki for the exact specifications for creating an artificial biome. If you do encounter any anomalies, ie. enemies from different biomes spawning, it's because most biomes need only 1 block to spawn enemies and plants. For example, you need a minimum of 1000 blocks to create a fully artificial desert biome, complete with background and music. However, 1 block of sand can still spawn waterleafs, antlions, vultures, and even hardmode NPCs.

Not an exact answer, but to help you in construction, listen for the change in music. Once you start to hear the biome-specific music, you know that you've successfully created an artificial biome.

1

The best way I found is to lay down about 1000+ tiles on either side of you, obviously using the blocks of the biome you want to create.

I've tried the same with making an underground corrupted biome. The world's in hardmode and I want the cursed flames spell, so I placed some ebonstone in a cave and, slowly but surely, it turned into underground corruption. I'd say this is a good set up for any artificial biomes.