Can You Reuse Mushroom Substrate for Another Flush (Answered)

You’ve successfully produced two or more flushes from your mushroom grow kit. But now what do you do with the leftovers? Can you reuse mushroom substrate? In this article we

• show you how to reuse mushroom substrate to get the most out of the organic materials,
• discuss the best tips for producing a successful flush, and
• answer all your questions about reusing mushroom substrate.

Growing your own mushrooms delivers so many benefits.

Not only is it rewarding to produce your own food from your very own garden, you know exactly what has been used (or not been used in the case of chemicals and pesticides) in growing the mushrooms.

The one thing that we, at the Garden Bench Top, love more than growing your own food, is when you are able to employ the three R’s – Reuse, Reduce or Repurpose. For example, using spent coffee grounds to grow mushrooms, or in this case, reusing mushroom substrate to try and grow another flush of mushrooms.

What is spent mushroom substrate?

Spent mushroom substrate is essentially the growing medium (or substrate) that remains in your mushroom growing kit once your mushrooms have finished growing.

Spent mushroom substrate is the leftover material in your mushroom growing kits.

It will look like a big, dry lump of moldy organic material. However, if you are familiar with mushroom cultivation, you will know it isn’t mold. Rather, the mycelium from the mushroom spores during the inoculation period.

During the mushroom growing process, the white mycelium fibers spread through the substrate, absorbing as many nutrients as possible from the organic materials feeding the mushrooms as they grow.

It is for this reason, why we always provide our mushrooms with a nutrient rich substrate with added supplements.

Each species of mushroom requires different nutrients and minerals to grow. For instance, oyster mushrooms require starch, lignin, fats, protein, nitrogen and sugars to grow. While, varieties of mushrooms utilize other minerals like calcium, magnesium, potassium and phosphorus.

And it is these different nutrient requirements between mushroom varieties that will allow us to reuse the substrate.

Reusing Mushroom Substrate

Now that we know what spent mushroom substrate is, let’s take a look at how we can use this to produce more mushrooms.

Is it possible to grow mushrooms on spent substrate?

Yes – it is possible to reuse mushroom substrate.

However, there are some important points to understand before you start trying to reseed your spent substrate.

Once your mushrooms have finished their growth cycle, it won’t produce any further flushes of mushrooms. This is primarily due to the mycelium exhausting the nutrient and mineral levels in the growing medium.

However, that does not mean there isn’t any more nutrients left in the spent substrate for other mushroom varieties. There are still unused nutrients and energy within the organic materials that other mushroom species can use to produce new flushes.

The main challenge is understanding which mushroom varieties will still grow in your spent mushroom substrate (discussed in the next section).

We think it is important to mention, don’t expect your mushroom substrate to last forever. You can expect a further one – two flushes of new mushrooms. And with each flush, the quality or quantity of the mushrooms may decrease.

After all, there is only so much energy in organic materials that can be utilized before they re-enter the circle of life.

Which varieties of mushrooms can be grown on spent substrate?

The answer to this question will depend entirely on the initial type of mushroom you grew on the mushroom substrate.

Since oyster mushrooms are a very popular variety of mushroom to grow around the world, we’ll use them in our example as the initial mushroom variety that grew on the fresh mushroom substrate.

It may surprise you to learn that the best variety of mushrooms to grow in spent (oyster) mushroom substrate is other varieties of oyster mushrooms (not the exact same variety).

For example, if you were growing King Oyster mushrooms in the first batch of your mushroom grow kit, suitable follow-on mushroom varieties would be Phoenix oyster mushrooms, or pink oyster mushrooms.

If you are using other varieties of mushrooms, like shiitake mushroom or the common button mushroom, we’d recommend doing a bit of digging around and seeing if you can find some suggestions for reusing the substrate from those particular grow kits.

How to prepare spent mushroom substrate

Okay, it’s time to get our hands dirty. Here are the steps for reusing your spent mushroom substrate:

1. Dry your substrate. Before you begin pulling apart your growing kit, it is recommended to dry your mushroom kit out by leaving it outdoors in a warm or sunny position. This is to extract all the excess water.
2. Separate your used substrate. Now it’s time to cut your substrate out of the initial mushroom grow kit. Usually, we always use sterilized tools and equipment when dealing with mushroom substrate. However, it won’t be a big deal in this process, because we will be sterilizing the substrate before you use it again.
3. Sterilize your substrate. To get rid of any unwanted bacteria or mold spores, we need to sterilize the organic material. You can use a sterilizing chamber if you have one. Alternatively, you can use a sterilizing formula and apply it to your substrate.
4. Break your substrate down. Use your hands to break apart the substrate block to a consistency that resembles soil (or as small as you can get it to crumble). You can add in some more organic materials to give your spent substrate a boost.
5. Ready for reuse. Now it’s time to restart the mushroom growing process. Add in the spores of your next variety of mushrooms, and prepare the grow kit as you normally would.

Frequently Asked Questions

In this section we tackle all the odd questions that may crop up while you are repurposing your mushroom substrate.

On a side note – if we don’t answer your question below, please reach out to us via our contact page and we;’ll be sure to respond as soon as we can. We’ll even feature your question in this FAQ section so other fellow gardeners can benefit.

Can you reuse mushroom substrate forever?

No – unfortunately, reusing mushroom substrate forever is not an option. The organic materials will eventually break down to a point where they will become unusable for a new flush of mushrooms. There simply won’t be enough nutrients or energy for the mycelium to absorb.

But that doesn’t mean it cannot still be used. We suggest adding any leftover substrate to your compost or areas of your garden that need a bit of a nutrient boost.

Can mycelium be reused?

In theory, mycelium should be able to survive as long as the conditions are maintained and there is enough food for it to absorb and grow. The challenge is keeping up with the mycelium’s growth. Mushroom mycelium grows quickly and absorbs a lot of nutrients. As soon as conditions are not optimal, or it runs out of food, it will begin to deteriorate.

How many times can you clone a mushroom?

The answer to cloning mushrooms is the exact same as the previous question regarding the number of times mycelium can be reused. In theory, you could ‘clone’ or regrow mushrooms an infinite amount of times, as long as the conditions and food availability is maintained. Along with keeping up with the mushroom growth, you also need to ensure competing bacteria and mold do not enter your mushrooms’ environment, and it remains sterile.

What’s Next?

If you have decided to give your used mushroom substrate some renewed life, check out our mushroom growing guides for detailed instructions on how to grow different types of mushrooms.