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I'm getting sick of gardening solely in pots, so I think I might spend my tax return on finally doing raised beds... plus it's a good excuse to get into the yard and do some work so I can forget about my day job for a couple of hours :-)

 

I was wondering - out of all the "recipes" for filling a raised bed, is mushroom compost a good idea? I don't have much in the way of organic stuff to go in the beds, so I was thinking of getting a delivery of mushroom compost and maybe mixing it with a delivery of garden soil.

 

Is this a good or bad idea?

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Check the pH of the mushroom compost - from reports it seems to vary and can be very alkaline. Better to get something about neutral to slightly acid so amending it later will be less of a hassle. Most of the usual plants we grow like that range exceptions are Blueberries and Strawberries and Potatoes.

 

Garden soil is stolen from somewhere else. I suggest a premium potting mix if you can get it delivered in bulk and shovel and barrow it yourself you'll get a lot more for your money than buying in bags. Plus the extra exercise ;-) Oh and check that pH too before you buy, either ask or better if you can take a meter or a pH test kit with you. If the landscaping supplier objects, go somewhere else. One of our forum members had pH 12 delivered and found it totally useless so a great waste of money, time and energy.

 

Once you get some mix into your beds you can bury each day's kitchen scraps to compost away. Then do a thick cover crop to lay a foundation of organic material. And make sure you can reach across your bed/s and not make them so wide you have to walk on them.

Same with Rudi, the bulk of the veggie beds I made at my parents' place were mushroom compost (bought 5 cubic metres as that's the minimum for delivery).  You'll have to check the PH as Elaine suggested as it varies depending on your source.  The problem I found is because it's all organic matters the volume of the beds shrink very quickly.  We top them up regularly with more mushie composts, dirt from the chicken run, horse manure, home made compost, a bit of sand, mulch  ... anything I can get my hands on really... 

The garden beds at my parents place are going great guns with lots of worms and as long as the chooks leave them alone, things  generally grow pretty well ;P unlike my place at the moment ...

Hi Florence - that's exactly what I'm planning on doing, as it's so much cheaper than other products. Where did you get yours from? I am looking at getting mine from the mushroom farm at Nth Maclean. Wondering whether to do a ph test beforehand. Thanks!
Hi Justine, that's where I got mine from... or the company who delivers the mushroom compost get their's from.  They said they've tested the ph at around 7... I tested a bit of it after I filled the bed, I think they were mostly around 7, it's still a good idea to test it yourself as it may varies from batch to batch and I don't think they test every batch.  Some veggies prefers slightly more acidic soil (6.5 or so) like tomatoes and potatoes, and mushie compost tends to retain water when it's wet I found... my potatoes didn't like it at all.  I would suggest mixing in a bit of course sand and some garden soil as well ~  All the best with your garden beds !

I was shocked at just how much it took to fill my raised beds.   I did the 'lasagne' layers, and really glad I did as I know have the yummiest 'soil' ever.  I got most of the stuff I needed from Redcliffe Produce at Rothwell. Their prices are good.

 

Not sure exactly what order I did it, the recipe is: 

sugar cane mulch (and see if you can get some really coarse stuff in a bale rather than the bags)

handfuls of blood and bone 

manure

mushroom compost

lucerne

(repeat the above so you have lots of small layers, rather than bulky ones)

Then the top layer is compost (you can buy it if you don't have any stuff yourself) which you plant into.

 

You won't be able to grow root veggies until it breaks down.  But since we're coming up to summer anyway, your corn / tomatoes / cucumbers (etc) will love it.  I promise.  :)

 

I did a raised bed and got potting mix delivered and and on the advice of my father inlaw only layered it once or twice with sugar cane, big mistake! The potting mix I was assured was great for growing veggies in but it was sooo dense and full of cLay. I mucst admit I have been able to grow plenty, but it's taking a long time to get it where I want it, when I think if you do what TRacy and Elaine say you will have better luck of having something great straight off

Just wanted to add a few thoughts that haven't been mentioned based on my experiences. 

Mushroom compost has a number of advantages:

  • It's a cheap bulk source of organic matter (helps improve texture and structure as a soil conditioner);
  • May have some nutrients;
  • Free source of mushrooms (growers have 3 flushes and then sell the spent compost but you often get a final flush or two at home);
  • It also holds moisture well; and
  • Forms a good soil crumb when it fully composts.

However, there are also disadvantages to be aware of: 

  • Mushroom compost varies widely from grower to grower.  The raw compost ingredients depend on what the mushroom farmers have bought in (i.e. what was available at the time).
  • Mushroom compost can have urea and artificial fertilisers in it.  Mushroom farmers also have to contend with fungus gnats and flies so many spray chemicals to treat these problems.  So there may be fungicide residues in the compost.
  • The compost itself is often chemically treated so only the particular strain of mushroom spores the grower wants will grow in it.  Mushrooms can't survive competition.  Steam pasteurising is another process that kills all microbes to make it a sterile growing medium.
  • Because it's sterile, it's effectively dead as a doornail in terms of microbial soil life.  We need beneficial microbes in our garden soil for plants to grow so they need to be introduced to activate this 'dead' organic matter if you are choosing to use it.
  • If purchasing in the plastic bags they are grown in, they can be really heavy, wet and messy to collect/carry home and whilst they are cheap to buy, the process of loading and unloading does take time and effort.
  • If left in the wet bags, the compost can become anaerobic or dry out if left too long and then become crusty.  (I've found it best to use quickly so tend to set aside time for a couple of days to build a bed, collect/unload compost and mix with other ingredients.)
  • Mushroom compost is (I know this sounds obvious!) fungal dominated.  Veggies and herbs prefer bacterial dominated compost so if you want to grow this kind of food, it's important to shift the abundance of microbes back towards bacteria by activating it with the right food.
  • pH as mentioned is often neutral (around 7) but can be quite alkaline which impacts mineral uptake.

A few tips if working with the mushroom compost:

  1. For those of us organic gardeners, all mushroom composts aren't created equal.  If possible, try to buy spent mushroom compost that has been used to grow Swiss Browns from your local mushroom farmer - as these are likely to be the least chemically treated. 
  2. Whilst mushroom compost is a source of organic matter, it doesn't mean the compost is organic (not chemically treated.)  So if you want to use it in your garden, some other options are to put it through your hot compost or activate the compost with microbes to accelerate breakdown.  Mixing in some zeolite can also help neutralise toxic substances.
  3. To accelerate breakdown, mix well with manure, blood and bone and lucerne and water in molasses to feed the beneficial bacteria present in the organic ingredients. Digging in food scraps is another option.
  4. If building a no-dig garden, I avoid layering mushroom compost using the lasagne method now although I used to do this.  Now if making a lasagne bed, I mix the mushroom compost well by forking it in with the other ingredients and find it composts much quicker.  Introducing an in-situ worm farm in a no-dig garden also encourages worms to breakdown the organic matter and convert to humus which will feed your plants.
Good luck!

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