How to Grow Mushrooms in a Box (Zero Skills Needed!)

If you’ve been disappointed with mushroom kits in the past, there is an easy – and far cheaper – alternative. It’s simple to try, involves no specialist equipment, and will have you picking your own mushrooms within just six to eight weeks. You’re going to love this method, I PROMISE!

Make Your Own Mushroom Growing Kit

All we need are six things to get started:

Crate: I use a simple plastic mushroom crate (you can often find these for free or at least very cheaply) to keep everything contained, or you can use a seed tray that’s at least 6in (15cm) deep.

Cardboard: To line your crate, use plain brown cardboard. As well as preventing your growing medium from falling out if you’re using a mushroom crate, it will stop the edges of the growing medium from drying out too quickly and help ensure a moist environment that your mushrooms will absolutely love. If you have a particularly sturdy cardboard box you could grow mushrooms in that alone, without the need for a crate, but a crate gives extra rigidity when the growing medium is moist.

Growing Medium: We’ll need something nutritious for the mushrooms to get their fungal teeth into, and for that I use well-rotted cow manure bought in bags from my local garden center. Avoid fresh manure, which will be just too rich for delicate mushrooms. It might sound odd, but I love manure! When you think about it, there’s something wonderful about the waste product of one being becoming the food source for another.

Alternatively, you could use any good quality, all-purpose potting mix, or a mixture of the two. I’ve trialled growing mushrooms in both pure manure and a 50:50 mix of manure and potting mix, and both perform very well.

Mushroom spawn: Of course you’ll also need mushroom spawn – the ‘seed’, if you like – which is widely available from online suppliers. Possibly the easiest mushrooms to grow are button or white closed cap mushrooms (Agaricus bisporus var. bisporus), just like the ones you’ll find in the supermarket. Button mushrooms are just the younger, smaller versions of larger white mushrooms you’ll see for sale, while Portobello mushrooms are white mushrooms that have completely opened out and reached full size. Or try some common brown mushrooms, also sold as chestnut or cremini mushrooms (Agaricus bisporus var. hortensis).

Additionally, you’ll need some newspaper to help keep moisture in, and a spray bottle for misting.

Mushrooms don’t need any light to grow, which means you could grow them in a shed or any suitable out-of-the-way space. And they are outrageously efficient growers; you could actually grow around a million pounds (nearly half a million kilos) of mushrooms on the equivalent of one acre of land! For comparison, that same land would grow just 28,000 pounds (12,700 kg) of potatoes.

Set Up Your DIY Mushroom Growing Kit

First give your trays a good scrub in warm, soapy water to get them clean and sparkling, then rinse them off and let them air dry. Even if they’re brand new, it’s a good idea to give them a quick wash and rinse to be on the safe side in case there are any spores of unwanted fungi lurking.

To prepare the manure, add a little water to make sure it’s nice and moist, but not sopping wet. If you squeeze it really tight in your fist some moisture should leak out, but there shouldn’t be torrents. If the manure is already moist, you won’t need to add any additional water. At this point you could also mix in some potting mix if you like. Fill your box about two-thirds full with the manure or potting mix, gently firming it down as you go and levelling it off to leave a smooth surface.

Then it’s time to add your mushroom spawn, which is usually supplied as cereal grains that have been colonized by mushroom spawn. They will look white from the mushroom’s mycelium (a bit like roots) which have taken hold on the grain. What the grain’s doing is simply acting as a delivery mechanism for our mushrooms, giving it something to survive on till it hits your growing medium.

Fungi, including mushrooms, are nature’s great recyclers, but did you know they actually have more in common with us humans than they have with plants, because they share more of the same DNA. Incredible right?!

Break up the grain spawn using clean hands, then mix the spawn into the top layers of manure for a good, even distribution. You can use anywhere between 2% to 10% of grain spawn to growing medium by weight. Higher ratios will give quicker colonization and faster results.

To keep your mushroom spawn snug, lay over and tuck in a few sheets of soaked newspaper to help hold in the moisture. To finish, pop in a label with the date and type of mushroom, just to help you keep track.

Incubation Time!

The tray now needs to sit in a dark, airy place for the next two to three weeks to incubate, during which time the mushroom mycelium will spread throughout the manure.

The best temperature for this is a fairly warm room temperature, but no warmer than 75°F (24°C) or you risk harming the spreading mycelium, and no cooler than about 60°F (15°C) or growth might stall. For me, at this time of year, that means bringing the trays indoors. If you don’t have a dark place to keep them, just lay a sheet of cardboard over the top.

Check your trays every few days, and if it looks like the growing medium is drying out a bit just give the surface a light misting. Remember it needs to be moist, not soaked.

After about 10 to 14 days, you’ll notice fine white threads forming. This is the mycelium successfully spreading throughout the box, and it means you’re most definitely onto a good thing! Within another week or so you’ll have a more solid spread of mycelium, turning the manure or potting mix almost pure white. This is an exciting moment, because we’re on to the next and final stage towards those lovely, moreish mushrooms!

Add the Casing

To get our mushrooms we need to add what’s called a casing layer. The purpose of this layer is to signal to the mycelium that the moment has come to produce the fruiting bodies – the mushrooms.

We need something that’s great at holding onto moisture, while also staying fairly light and fluffy so we get good airflow. The solution is a 50:50 mix of coconut fiber and vermiculite.

Coconut fiber retains plenty of water, which is essential for mushroom formation, while the vermiculite will prevent compaction, ensuring excellent air exchange – oxygen in, and carbon dioxide out. Mix the coconut fiber and vermiculite together and, if it’s a bit dry, spray then mix in some water to ensure a good, damp casing material.

Lay this casing layer over the top of the mycelium to a little over an inch (3cm) deep. Then pop your mushroom box back into a dark, well-ventilated spot. The temperature can drop ever so slightly to something more like a cool room temperature, or between about 60-66°F (15-20°C).

At this point we need to watch our boxes carefully. I check mine at least once a day, and spray a fine mist frequently to maintain high humidity and to keep the casing layer moist.

Time to Pick Your Mushrooms!

Within another two weeks or so you’ll start to see tiny mushroom pins pushing through the casing. Continue to keep everything moist and they’ll double in size almost overnight until, usually within a week, you’ll be harvesting your mushrooms.

Once the caps have reached the size you want, it’s harvest time. I like to pick them when they are fully formed but still closed underneath. Just twist and pull the mushrooms gently from the base. Don’t cut them, as this will leave a stump which is then likely to rot and cause problems for the mushrooms still to come. Gently cover the hole left behind with a little of the surrounding casing material.

You should get several flushes of mushrooms over the next few weeks, with mushrooms produced here and there, steadily, rather than all at once right across the surface. Once they finally run out of steam, simply dump out the spent growing medium onto your compost heap or garden beds where it makes fantastic fertilizer for your garden, completing that wonderful circle of life!