Life Fruit

Nothing grows until you have put down one of the mechanical bosses, and anything you find before that is useless anyway, because the fruit refuses to be eaten until your health is already capped from crystals. It is a second, later staircase rather than a continuation of the first, and it ends at a hard ceiling that no amount of extra fruit will push past. The only thing that goes above that ceiling is a Lifeforce Potion, and only while the buff lasts.

The obvious move is to eat it. The better one is to shimmer the first fruit you find into an Aegis Fruit and take the permanent defense instead, which does more for your survival at that point in a run than one more segment of health does. Do that once, then eat every fruit after it.

Jungle grass, anywhere in the underground layer or below. That is the whole rule. It does not have to be inside a real jungle biome, it does not have to be off screen, and grass you planted yourself counts exactly the same as grass the world generated. The one restriction is spacing, since two fruit will never grow near each other, so a farm has to get wider rather than denser. Growth also runs faster in Expert.

Long platforms of jungle grass underground, spread with Jungle Grass Seeds, then leave it alone. You do not need to clear the existing plants first, because fruit will replace spores, bushes, vines and thorns as it comes in. Bee hives are the exception. They will not be replaced and they will squat in spots you wanted, so running a line of platforms under each grass row stops them forming. Background walls do not block growth, so an enclosed farm works fine.

The Spelunker buff highlights them the way it highlights ore, and a Metal Detector ranks them above everything else in range. That is enormously useful while you are collecting and genuinely irritating afterwards, because one stray fruit you never picked will mask every chest and vein near it for the rest of the run. On the minimap they read as a small pale green square against the darker foliage. Fairies will lead you to them as well, and if you mapped a lot of underground jungle before Hardmode, retracing those old tunnels with the detector out beats exploring new ones. They come loose to any weapon or tool, so you never need to swap to a pickaxe, and breaking the grass under one knocks it down too.

Spraying a stretch of jungle with dark blue solution converts it to glowing mushroom, which knocks every fruit in the area loose and leaves the items lying on ground bright enough to pick them out against. Sweep them up, then paint the biome back green. Stop doing this the moment Plantera bulbs can exist in your world, because the same conversion pops them and starts that fight wherever you happen to be standing.

Once you are capped, spare fruit still goes into Jungle Juice, and a rubble tool will put them back into the world as decoration if you prefer them on the wall.