Mushroom Harvest Interval Calculator
Work out how many days to expect between flushes, when the next harvest window opens, and how much that flush is realistically worth picking.
Next harvest expected
—
How the interval was built
Harvest window and yield
What to do with this
Overview
A mushroom block does not stop producing after the first harvest. It rests, repairs the mycelium it spent on that flush, pulls water back into the substrate, and then pins again. The gap between one harvest and the next is the harvest interval, and it is the single most useful number a grower can put on a calendar. It tells you when to free up fruiting-chamber space, when to line up a market delivery, and when a block has simply stopped paying for the shelf it occupies.
This calculator estimates that interval for seven commonly grown species using the factors that actually move it in a real grow room: species biology, the flush you are waiting on, fruiting temperature, humidity during recovery, substrate size, and whether the block was rehydrated after picking. It then converts the interval into a dated harvest window and a realistic fresh-weight estimate for that flush.
It is built for small commercial growers planning production runs, market gardeners scheduling deliveries, farm-shop suppliers managing standing orders, and serious home cultivators who want to know whether a fourth flush is worth waiting for. If you have ever stared at a spent-looking block wondering whether to soak it or bin it, this is the number you were missing.
How it works
- Pick your species. Interval behaviour differs sharply between them: pink oyster turns around in about a week in warm conditions, while shiitake sawdust blocks routinely take three to four weeks between flushes.
- Choose the flush you are waiting on. The second flush follows the first quickly; every flush after that takes longer as the mycelium runs down its nutrient reserves.
- Enter the date you picked the previous flush. This anchors the projected harvest date and window.
- Enter the substrate weight at spawning, in kilograms or pounds. Yield is calculated as a share of this weight, and larger blocks recover slightly more slowly.
- Enter the fruiting area temperature and average humidity during recovery. Temperature drives metabolic rate more than any other controllable factor; low humidity stalls pinning.
- Select how the block is rehydrated after harvest. A cold soak shortens recovery and protects yield; doing nothing extends it and costs you mushrooms.
- Press Calculate interval. You get the total interval, the two phases that make it up, a dated harvest window, a yield projection, and a plain reading of whether the block is worth keeping.
Formula explanation
The interval is split into two phases. The recovery phase runs from harvest to the first visible pins and is where nearly all the variation lives. The maturation phase runs from pinning to picking and is mostly a function of temperature.
What each part means
- Rate factor is a Q10-style temperature response: every 10 degrees Celsius away from the species optimum roughly halves or doubles metabolic rate, capped at realistic limits. Outside the species' viable range it takes a further penalty, because flushes stall or abort rather than simply slowing down.
- Rehydration multiplier ranges from 0.86 for a full 12–24 hour submersion up to 1.22 for a block left dry. Water is the limiting resource in a second or third flush, not nutrition.
- Flush multiplier adds roughly 22% to the recovery phase for each flush beyond the second, reflecting declining mycelial vigour.
- Humidity multiplier applies a penalty below 85% relative humidity, where pin initiation slows and aborts increase.
- Size multiplier adjusts modestly for block mass: a 5 kg block takes a little longer to recolonise its surface than a 1 kg one.
- Decay ratio is the share of the previous flush's yield you can expect, typically 0.4 to 0.7 depending on species. It is why a fourth flush on king oyster is rarely worth the shelf space.
Practical benefits
- Plan production, not guesswork. A dated harvest window lets you commit to market days and wholesale orders weeks ahead instead of promising volume you cannot confirm.
- Decide when to retire a block. When the projected yield drops below roughly 3% of substrate weight, the block is costing you more in space, labour and contamination risk than it returns.
- Justify a temperature change. Seeing what a four-degree drop does to your interval makes the cost of heating, or of cooling in summer, a straightforward calculation.
- Value the soak properly. The difference between misting and a proper cold soak is usually several days and a meaningful share of the flush. The tool puts numbers on it.
- Rotate fruiting space efficiently. Knowing the recovery phase separately lets you move resting blocks out of the fruiting chamber and bring fresh ones in.
- Set expectations for staff and customers. A written interval and yield estimate is far easier to hand over than accumulated intuition.
Frequently asked questions
The usual causes are moisture and air. A block that lost more than about 20% of its weight during the first flush may not recover fully from a short soak, and a long interval is really a dehydration problem. Poor fresh-air exchange is the other common culprit: carbon dioxide build-up suppresses pinning without producing any obvious symptom. Also check that your thermometer is reading the substrate surface rather than the room, since the two can differ by several degrees in a well-stacked fruiting chamber.
Commercially, most growers take two flushes and then recycle the substrate, because the third rarely covers its handling cost. Oyster and shiitake blocks can genuinely produce three or four flushes; king oyster usually gives one strong flush and a weak second. Home growers with no space pressure can push further, accepting that later flushes are smaller, slower and more prone to picking up competitor moulds through the open harvest wounds.
For shiitake and oyster sawdust or straw blocks, a cold-water soak is standard practice: weigh the block first and soak until it returns to roughly its post-colonisation weight, typically 4 to 12 hours, using cool clean water. Going beyond 24 hours starts to drown the mycelium and invites bacterial souring, so the longest setting in this tool is best reserved for badly dried shiitake blocks. Casing-layer crops such as Agaricus and outdoor wine cap beds should be watered rather than submerged.
It matters less for timing than for contamination. What matters most is removing the whole cluster base cleanly, because leftover stump tissue rots and becomes an entry point for bacteria and moulds, which can delay or ruin the next flush. Twisting the entire cluster free tends to leave less debris than cutting the stems partway up. Whichever method you use, clear away any fragments and let the harvest surface dry briefly before returning the block to high humidity.
Disclaimer
This calculator provides general planning estimates based on published cultivation ranges and typical commercial practice. Actual harvest intervals and yields vary with strain, substrate formulation, colonisation quality, air exchange, water quality, and hygiene, and may differ substantially from the figures shown. Nothing here is agricultural, commercial, financial, or food-safety advice. Always identify and inspect mushrooms before consumption, follow local food-handling regulations, and consult a qualified adviser before making production or purchasing decisions. No warranty is given as to accuracy, and no liability is accepted for any loss arising from use of this tool.
