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    Spawn rate calculator

    Spawn rate is the weight of spawn as a percentage of the bulk substrate you mix it into. Enter your substrate and a rate to see how much spawn to add, or enter the spawn you have to see how much substrate it covers.

    Spawn rate calculator

    What do you want to find?
    lb

    One block or a whole batch, hydrated and ready to inoculate.

    %

    Spawn as a percentage of the substrate's weight.

    Spawn to add

    0.25 lb (4 oz)

    • 5 lb of substrate × 5%
    • 5% is a ratio of 1:20, spawn to substrate

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    How does the spawn rate calculator work?

    • Spawn = substrate weight × spawn rate ÷ 100
    • Substrate covered = spawn weight ÷ spawn rate × 100

    For example: At 5%, a 5-lb bag of sterilized sawdust takes 5 × 0.05 = 0.25 lb of spawn, which is 4 oz. Turned around, a 5-lb bag of grain spawn covers 5 ÷ 0.05 = 100 lb of substrate at that rate, or twenty 5-lb bags.

    • A ratio says the same thing: 1 lb of spawn to 10 lb of substrate is 1:10, or 10%.
    • The calculator works by weight. Weigh both, or measure both by volume; the two don't give the same number.
    • Use more spawn on pasteurized or other non-sterile substrates than on sterilized ones.

    Where do the numbers come from?

    Every formula and figure on this page is from one of our grower guides, which cite their sources: extension services, farm trials and published studies.

    Common questions

    What spawn rate should I use?

    Use about 5–10% for oysters on pasteurized straw (UF/IFAS) and about 1–3% on fully sterile substrates (GroCycle). GroCycle gives 5–20% for non-sterile substrates in general. In a Fungi Ally trial reported by Cornell, one 5-lb bag of spawn colonized 100 to 200 lb of supplemented sawdust for shiitake, which is 2.5–5%.

    Does more spawn mean more mushrooms?

    Mostly it buys speed. Cornell's Small Farms Program says more spawn makes the mycelium grow through faster, but the substrate likely won't produce more mushrooms, so you spend more on spawn per pound. In a Penn State trial on an oyster species, spawning at 3.75% of wet substrate weight brought production about 9 days sooner than 1.25%, and yield peaked at 3.75–5%.

    Can I use less spawn to save money?

    Up to a point. In the Fungi Ally trial, one 5-lb bag colonized up to 200 lb of substrate in about 8 weeks, but at 250 lb colonization slowed and contamination rose. Cornell suggests starting high on a first grow, then lowering the rate as you dial in your process.

    Where does Hypha come in?

    In Hypha, a family tree links each culture, spawn bag and block to its parent, so you can see which spawn a block came from. Each bulk block gets a reminder to move into fruiting, then flush reminders.

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