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Spent mushroom compost

PlantmindedPlantminded Posts: 3,580
in Plants
I’d welcome other gardeners’ views on the merits of using spent mushroom compost please. I have sandy, free draining soil which gets very dry in summer.  Would this be a good addition to help retain moisture, avoiding use on ericaceous plants?  I’m planning on using it as a targeted mulch around key shrubs and trees as well as a general mulch on a perennial border.  I’m going to avoid using it near any ornamental grasses as it may be too rich perhaps?  Any thoughts gratefully received, thank you.
Wirral. Sandy, free draining soil.


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  • foxwalesfoxwales Posts: 69
    It's packed full of organic matter so is great soil improver.  I've put in 8 tons of the stuff into my borders over winter.  Go heavy with it to help retain moisture.  I wouldn't say it's overly rich because it's spent from the mushroom growing.  Weeding it is a dream as you can pull weeds out by hand, including dandelion and other long tap root weeds! 
  • PlantmindedPlantminded Posts: 3,580
    Thank you @foxwales, that’s really helpful. Delivery now on order!
    Wirral. Sandy, free draining soil.


  • borgadrborgadr Posts: 718
    edited March 2023
    I used a load of the stuff this winter for mulching, and I have to say it's a lot easier to work with than well-rotted manure (more fibrous and less clumpy, and without the dense clods that the blackbirds like to flick onto the lawn) though I believe it does contain some proportion of manure.
  • Pete.8Pete.8 Posts: 11,340
    I use mushroom compost from CPA Horticulture.
    I get 40 x 75L bags delivered in Sept/Oct.
    I find it's still quite hot on delivery, so I leave it over winter and have just started spreading it now. The bags have worms in them now which shows it's safe to spread.
    It is very good stuff, but do bear in mind it contains chalk, so is quite alkaline and therefore not suitable for all plants.

    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • GardenerSuzeGardenerSuze Posts: 5,692
    I used it too when we first started our garden. It did help to break up the clay. The only downside is to be aware of acid loving plants as said. You will get a few mushrooms appearing but no problem.
    I have worked as a Gardener for 24 years. My latest garden is a new build garden on heavy clay.
  • PlantmindedPlantminded Posts: 3,580
    Thanks very much for your thoughts @borgadr, @pete8 and @gardenersuze. I was unsure whether composted farmyard manure might have been a better option but as I grow a lot of grasses I thought there might be too much nitrogen in it.  In the supplier's description of the mushroom compost it states "may contain straw".  Is this a bad thing?  It probably takes ages to break down but I would have thought that it helps to aerate the soil and thereby aid wetting.  I'd be interested in your thoughts on this.
    Wirral. Sandy, free draining soil.


  • Pete.8Pete.8 Posts: 11,340
    edited March 2023
    Yes it does contain straw - which is great for improving the soil texture.
    The mushroom compost I buy is blended with poultry manure.
    My soil is slightly acidic clay, so is ideal for mushroom compost.
    I grow a lot of soft fruits which won't like the alkalinity, so I buy composted horse manure for them.
    I sometimes come across lumps of chalk in the mushroom compost that I discard.
    This is the mushroom compost from CPA- 


    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • PlantmindedPlantminded Posts: 3,580
    Many thanks @Pete.8, that's very helpful.
    Wirral. Sandy, free draining soil.


  • GardenerSuzeGardenerSuze Posts: 5,692
    It certainly helped to aerate my soil, the clay was so thick in parts when we moved here you struggled to plant.It did break down very quickly so we did order more over three years. One year it was very broken down on arrival another batch took longer. So it did vary but I don't know what I would have done without it in the early days.
    I have worked as a Gardener for 24 years. My latest garden is a new build garden on heavy clay.
  • borgadrborgadr Posts: 718
    Both mushroom compost and horse manure will usually contain some amount of straw (the latter which is the bedding from the stables)
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