Sizu Riatto
Flush Hour · Chapter 6

The Spawn Run

Know which day to expect a white tub, and plan the harvest on your calendar. Distance = rate × time, the spawn points' spacing, and a calendar that counts forward from the day you mix.

Home › Calculators › The Spawn Run

Opens on the book's tub. Change any number to your own and press Calculate.

The spawn run

The calendar (day 0 = the day you mix the spawn in)

Enter the spacing and a growth rate, then press Calculate.

The formula

  • Each spawn point grows halfway to its neighbor: distance = spacing ÷ 2
  • Time = distance ÷ rate; the rate your tub achieved = distance ÷ the days it took
  • A lab dish of agar is not a tub of straw: the model's days and your days differ, and the gap is information
  • Calendar: harvest n falls on day (first harvest + (n − 1) × days between flushes)
  • °F = °C × 9 ÷ 5 + 32; the straw's core runs 3 to 6 °C (5 to 10 °F) warmer than the room
The book's worked example, Chapter 6. The book's spawn points sit about 2 cm apart, so each grows 10 mm to meet its neighbor. At the agar rate, 11.7 mm a day at 25 °C, that takes 0.85 days; the straw at 24 °C (75.2 °F) takes 18 days, about 0.56 mm a day. The calendar: move to fruiting on day 18, pins on day 22, harvests on days 25, 39 and 53.
Check it. Write down the day you expect your tub to be fully white, and check it in Chapter 11.

Honest limits. The growth rate is one lab's agar measurement: straw, strain, spawn rate and temperature all change the real days, and published home guides say 2 to 3 weeks. Hot cores above about 30 °C can kill the mycelium; keep the room near 24 °C. The book's tub, its straw and its harvests were worked out on paper from published figures, not grown by us: weigh your own. Prices are illustrative, as seen in November 2026 (US mid prices, with UK beside where they differ), shown without a currency sign; put in your own. No yield or profit is promised. Everything stays in your browser: no sign-up, nothing stored.