Subsequent flushes

A colonised block usually has more than one flush in it. Each is smaller than the last, and each carries more contamination risk than the last, and at some point the arithmetic stops favouring you.

Knowing where that point is separates growers who produce steadily from growers who lose a shelf to Trichoderma chasing a quarter pound.

What to expect

Flush	Typical yield	Time after previous
First	100% (baseline)	—
Second	40–60%	7–14 days
Third	15–30%	10–21 days
Fourth	Under 15%	If at all

Most home growers get two good flushes and a marginal third. Commercial operations frequently run one and compost the block, because block space and contamination risk cost more than the marginal yield.

The routine between flushes

1. Harvest cleanly. Whole clusters, every stem butt out. This matters more for flush two than it did for flush one — see contamination mid-flush.

2. Let the surface dry, about a day. Reduce misting. A dry wound recovers; a wet wound goes bacterial.

3. Resume normal fruiting conditions. Humidity back to 90%, fresh air as before.

4. Wait. The block needs to rebuild before it pins again. Doing nothing for a week is the correct action and the hardest one.

5. Watch for pins, then treat it as a normal flush.

Rehydrating

Blocks lose water with each flush, and by flush three a sawdust block can be noticeably lighter. Rehydration helps — carefully.

Dunking: submerge the block in cool clean water, weighted down, for 4–12 hours. Drain thoroughly.

The risks are real:

Non-sterile water on a wounded surface. Use clean, cool water. Not warm — warm water encourages bacteria and is closer to the temperature everything unwelcome prefers.
Waterlogging. More than about 12 hours and you create the anaerobic conditions that cause Rhizopus and bacterial problems.
Contaminated blocks spreading. Never dunk a block showing any contamination, and never dunk several blocks in shared water if one is suspect.

Do not dunk immediately after harvest. Give the surface its day to dry first.

For monotubs, dunking is impractical; misting more heavily between flushes is the usual substitute, and it works less well.

When to stop

Compost the block when any of these is true:

Visible contamination. Not negotiable — see diagnostics and get it away from your other blocks.
The block has gone soft or is falling apart. The mycelium has consumed the structure.
Two consecutive flushes with nothing. It is done.
Yield below roughly 15% of first flush. The space is worth more than the mushrooms.
It smells sour or off.

There is no prize for a fifth flush. There is a real cost to keeping a declining block next to healthy ones.

Why flushes decline

Three things, all unavoidable:

Nutrition is finite. Each flush consumes substrate that does not come back. Supplemented blocks have more to give and decline more slowly — that is what supplementation buys.

Water is lost. Every flush removes water as mushrooms, and mushrooms are around 90% water.

Structure degrades. The mycelium digests the substrate that holds it together. Eventually there is no substrate left to hold.

Getting more out of a block

Supplement properly at the start. Master’s Mix outperforms plain sawdust across the block’s whole life, not just the first flush.
Higher spawn rates give more established mycelium and better later flushes.
Harvest before spore drop. Sporulation is expensive for the block.
Do not let it dry out between flushes.
Keep temperatures stable. Swings cost pins at every flush, and later flushes have fewer to spare.

When it is finished, the block still has uses.