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Hydrated Lime

4.67 out of 5
(6 customer reviews)

£1£9 (incl. VAT)

Low magnesium hydrated horticultural lime, otherwise known as calcium hydroxide. Suitable for cold water lime pasteurisation of straw for aggressive mushroom strains like most oyster varieties.

Note that this is NOT your typical builders lime/garden lime/dolomite lime which contains high levels of magnesium lime which will kill mycelium. We use this premium, low-magnesium lime in our own commercial operation to pasteurise straw when growing oyster mushrooms, so can vouch for it’s effectiveness. Don’t settle for inferior lime, as you’ll be very disappointed.

Cold water pasteurisation using lime is a low energy, cost effective method of pasteurising straw or other substrates ready for colonisation.

The added lime increases the PH of your soak solution to 11 – 13 PH, which is extremely alkaline and kills off bad competitor organisms.

Due to the high PH, we recommend wearing correct protective gear when handling hydrated lime as it can irritate the skin, eyes and lungs if inhaled. Wear glove, goggles and a mask and handle carefully.

The water solubility of lime is between 1.89 – 1.73 g/L (0°C – 20 °C). For example: if you are cold soaking straw in a 50 gal drum, for 200 litres of water, you’ll need approx. 350g of lime. Leave to soak for 10-24 hours for correct pasteurisation.

During the pasteurisation, the PH of the lime solution will normally drop to 6-8. This is normal but can vary. If your resulting water has a PH of more than 8, consider using citric acid to neutralise the water before disposal.

Wood ash can also be used for pasteurisation of straw, or used in combination with the lime soak to add additional nutrients to the substrate.

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£1£9 (incl. VAT)

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Cold Water Lime Pasteurization For Growing Mushrooms

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6 reviews for Hydrated Lime

  1. 5 out of 5

    Jack N

    works as it should for lime pasteurisation of straw for oyster production. Note that not all lime will dissolve completely so you might have some sediment left at at the bottom as I did, though initially that I had something other than lime, but after running a PH test, it was at 13.5. Further research showed that lime has limited solubility in water… cheers, Jack

  2. 5 out of 5

    C. Boyd.

    I personally believe lime pasteurisation is better for the environment than steam or other methods

  3. 5 out of 5


    Finding low magnesium gypsum is hard in the UK, due in part thanks to their lack of adequate labelling showing exact material compositions. After many failed attempts trying various brands, I finally bought some online. Buying from a mushroom supplies company, you know it's the right stuff. Mycelium is growing strong on my chopped straw as we speak, excited to get my harvest!

    The previous commenter Stephen was right, you really don't need too much of this stuff to raise the pH to suitable levels.

  4. 5 out of 5


    was struggling to find horticultural lime in my area, never heard of hear me raw before but offers products I need at good prices. will use again

  5. 5 out of 5

    Stephen Mueller

    Seems to work well for pasteurising straw and you don't need too much. Fast delivery. No complaints

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