Fruits growing sideways or inside the bag

Mushrooms are growing in the wrong direction — flat against the block, curling back toward the substrate, or forming inside a sealed bag where they’ll never develop properly.

Nothing is diseased. Fruiting bodies orient themselves using three signals, and one of yours is pointing somewhere unhelpful.

The three signals

Gravity (gravitropism). Stems grow up, caps orient horizontally so the gills or pores face down. This is the strongest signal for most species and it’s why a block turned on its side mid-flush produces mushrooms with a right-angle bend in the stem — they reoriented partway through.

Fresh air. Fruiting bodies grow toward higher oxygen and lower CO₂. In practice this means toward the hole you cut. This signal is why lion’s mane fruits from the single slit you made rather than from wherever it feels like.

Light. Weaker than the other two for most species, but real. Oysters in particular will lean toward a light source and will pin preferentially on the lit face.

When these conflict — the hole is on the underside, the light is behind, the block is lying down — you get the shapes you’re looking at.

The specific situations

Fruiting inside a sealed bag

The mycelium found a gap between the substrate and the plastic and pinned into it. The fruits are chasing the small amount of air trapped there.

What to do: cut the bag open over the pins immediately. They will usually recover and develop normally if caught within a day or two. Pins that have been squashed flat against plastic for a week generally won’t.

Cause: the bag wasn’t opened when the block finished colonising, or the block was left too long in a “resting” phase. Once a block is fully colonised and consolidated, it wants to fruit, and it will find somewhere to do it.

Growing sideways out of the block face

Normal, and usually fine. A block fruiting from a vertical face produces mushrooms that grow out horizontally then curve upward. Oysters do this naturally and the shelving habit is what they’re built for.

Only a problem if the caps are curling back into the block face or growing into each other. Rotate the block so the fruiting face is on top, or cut the next flush’s hole higher up.

Long stems bending in several directions

That’s a CO₂ problem, not an orientation problem — the mushroom is searching for air. See long thin stems and tiny caps.

Fruits growing down into the substrate

Uncommon and usually means the block moved after pinning. Pins set their orientation early and re-orienting costs them energy and shape.

What to do: leave the block alone once pins have set. Deciding at day three that the tub would look better on the other shelf costs you the flush.

The practical rules

1. Cut fruiting holes where you want mushrooms. They go to the air. This is a feature — it’s the entire technique for getting one clean lion’s mane fruit instead of five ragged ones.
2. Position the block before pinning, then don’t move it. Orientation is set in the first 48 hours.
3. Put light above, not to the side, if your species responds to it.
4. Give clusters room. Oyster clusters growing into each other deform for purely mechanical reasons.
5. Open bags on time. Check colonised blocks every couple of days. A block that’s ready and still sealed will pin internally.

Species that fruit sideways on purpose

Before treating this as a fault, check the species page:

• Oyster mushrooms shelve laterally. That’s their normal habit.
• Reishi forms flat conks that grow horizontally by design, and produces antler-form growth instead under high CO₂ — deliberately, in many grows.
• Turkey tail grows as thin lateral brackets.

Wanting these to grow upward like a button mushroom is wanting the wrong thing.

---

Mushrooms grow toward air and away from gravity. If yours are pointing somewhere strange, one of those two is somewhere strange.