Skip to Content

How to Grow Portobello Mushrooms: 3 Popular Methods Even The Beginners Can Understand

Ever wondered how to grow portobello mushrooms? The process is simpler than you imagine. Also if you are someone who has never had a green thumb, you would be able to still achieve a success rate in growing these delicious ingredients at home.

Whether it is in a greenhouse or a small planting bed, you can choose an option that works best for you.

Besides being delicious, this is also the edible mushroom variety that comes loaded with nutrients like Vitamin D, potassium, carbohydrates, and others.

The signature rounded shape of these mushrooms, and their white stem helps you distinguish them from the other types of mushrooms. Being cholesterol-free substitutes for meat, they can give a rich taste to any recipe.

There are different methods to follow, depending on where you plan to grow your mushroom. Let’s look at the step by step procedure to grow portobello mushrooms easily.

How to Grow Portobello Mushrooms

What Will You Need to Start Growing Portobello Mushroom?

There are 3 popular ways to grow portobello mushrooms at home. Here is what you need for each of these methods-

Growing portobello mushrooms from ready to use kits

These are complete grow kits that come with:

  • Substrate for growing mushroom
  • Spores planted in the substrate

Growing portobello mushrooms from spores indoor

  • Growing tray
  • Portobello mushroom spores
  • Peat moss
  • Compost

Growing portobello mushrooms from spores in the garden

  • Compost
  • Peat moss
  • Material to construct a raised garden bed
  • Portobello mushroom spores

How to Grow Portobello Mushrooms – 3 Popular Methods

Method 1: Growing portobello mushrooms from ready to use kits

1. Ease of Growing

This is the most straightforward procedure for absolute beginners. The other two methods are easy as well, but it takes some effort and patience from your side.

If you do not have enough space or if you would need the simplest way to do it, go for a ready to grow mushroom kit. With this, you can effortlessly grow portobello mushroom and within a shorter duration.

2. Calculating the Yield

Most kits come with spores embedded in a growing medium. Pick the right sized kit or combine 2 or more kit. The yield might be relatively lower with the ready kits, and therefore you should plan your purchase accordingly.

Once you get the substrate, you would be able to use it directly out of the box. Some of them can be used within the packaging box, where there is a growing window provided.

3. Adding moisture

Mushroom growing kit - How to Grow Portobello Mushrooms

Wet the substrate as instructed in the pack. Most of the grow mediums comprise of some plant-based soil or natural materials.

Some of them should not be opened until the date you plan to plant them. Misting would be sufficient to activate the spores and start the growth. Regular misting might be required to prevent the medium from drying out.

4. Growth and harvest

Choose a dark spot in your kitchen to obtain the best success rate with the kit. Temperatures around 60℉ to 80℉ might be optimal for the growth of portobello mushrooms.

On giving the medium enough wetness and the ideal temperature, mushrooms should be ready for harvest in a week or two.

Method 2: Growing portobello mushrooms from spores indoor

1. Choose the right tray size

Pick a wide tray where you can place the planting medium. It doesn’t have to be a deep trough as you would need with other plants. Ideally, 8 inch is enough depth for the healthy growth of mushrooms.

If you would like to start small, a 6 inch x 6 inch square should be sufficient, to begin with. The width depends on the quality of the spores you have at hand.

The depth is what matters more in this case. For growing a good supply for the whole family, you can use a 4 ft by 4 ft tray.

2. Add compost

While growing mushrooms indoor, a mixture of compost and peat moss would be the best choice of growing medium to create.

Peat moss comes later on the top, and you should begin filling the tray with compost. Nutrients in the compost would help activate the spores and initiate the germination.

At least a 6-inch depth of the tray should be composed of compost alone. Compost that you prepare at home or store-bought compost can both be used. Make sure that you do not choose chemical fertilizers which are likely to seep into the mushrooms.

3. Planting the spores

Place the spores as a thin layer on top of the compost. Spread it out evenly, and the spacing would not be a big problem in this case. Make efficient use of the space you have on the tray and avoid overcrowding. Once you spread the spores, press the layer onto the compost layer gently.

4. Add peat moss

Similar to the needs of a growing kit based mushroom cultivation, you should give your compost tray with the mushroom spores a dark and damp spot. The first stage after the germination of spores would be the appearance of tiny white spots.

This would be the right stage to add peat moss. Peat moss helps enhance the growing environment by adding just enough dampness without letting water stagnate.

5. Growth phase

Portobello mushrooms can make a great hobby as they are effortless to care for. The growth medium doesn’t need sunlight, and you do not have to water it often.

The medium should be damp, and when you place it in a dark spot, the peat moss layer doesn’t dry out easily. Therefore, observe the peat moss layer and mist it when required.​

Agaricus bisporus mushroom - How to Grow Portobello Mushrooms

You can even add a layer of newspaper on top of the peat moss to glow down the evaporation of water. As the mushrooms start growing out of the peat moss, you can remove the paper and let the mushrooms grow and expand.

Temperatures around 60℉ to 80℉, similar to the requirement for a ready mushroom kit, would be good for the mushroom growth.

6. When to harvest?

Portobello mushrooms grow big the longer you leave them in the medium. The stage where you see the growth above the peat moss layer, there are young mushrooms ready for harvest.

However, for them to grow bigger, you might have to wait a bit longer. Do not stop misting the peat moss once the mushroom grows. Till the day of harvest, it is better to continue misting to maintain the best texture of the mushroom when you pick it.

Method 3: Growing portobello mushrooms from spores in the garden

1. Picking the right season

Growing the portobello mushroom lot in the garden can be slightly tricky. When you grow it indoor, you have full control over the temperature and light settings that you provide.

However, you cannot do this with the garden growing bed. Another huge benefit of growing indoor would be the fact that you can continue harvesting them throughout the year, no matter what the temperature is like outside.​

When you grow mushrooms outdoor, you should make sure that you pick the right season to grow. The ambient temperature should not be outside the range 50℉-70℉. Temperatures lower than or more than the intended range can affect the growth.

2. Construct the bed

Any garden bed would be beautiful. But to prevent accidental treading over the bed and to improve the convenience of harvest, you can choose a raised bed.

How to Grow Portobello Mushrooms Raised Garden Bed

You can construct one with wood easily. The dimension can be finalized based on the garden space available. A huge benefit that the raised beds offer is the ability to alter the soil you use.

You would also be able to modify the temperature, which is not possible with the natural garden bed where the ground temperature keeps fluctuating.

Raised beds also make it easy for you to add the intended compost and fertilizer to speed up the growth and improve the quality of mushrooms.

Besides wooden beds, concrete variants are also available. You can choose one that works best for your needs and the size you pick. Maintaining 8 inches depth as with the indoor growing tray would be necessary even with outdoor nurturing of the portobello mushrooms.

3. Fill compost

Growing mushrooms in the garden are somewhat similar to growing them in the kitchen. The first step here is to fill compost.

Filling to a dept of 6 inches would be required in this case as well. This gives a thicker layer of nutritious medium for the spores. Before you sprinkle the spores here, you would be sterilizing the growth medium.

For this, a thick layer of cardboard is required on top of the compost layer. An opaque sheet placed on top of the cardboard further increases the heat and gets the job done.

Leave this arrangement unaltered for at least 2 weeks. Spore planting only begins afterward. So, you can calculate the time taken for harvest accordingly and plan when to prepare the beds.

This helps you start right when the soil temperature gets warm enough for the cultivation of these mushrooms. Executing this step, as you can see, is not essential while growing indoor. It helps sterilize and ready the medium for offering optimal growth.

4. Planting the spores

Given that you have a larger area with outdoor growth of mushrooms, you can pick a bigger batch of spores. Spread out the spores evenly and then press them into the compost as you do with indoor growth trays.

This helps the spores get nicely attached to the growing medium and prevents the spores from being blown away.

5. Add peat moss

To ensure that your spores have started germinating, wait till you notice a growth on top of the compost layer. Before you add peat moss, you should see tiny spots on the soil.

This is the stage where you add a payer of peat moss to fill the bed till the top. Peat moss is porous and aids easy penetration of water into the layer of spores below it. Misting would be sufficient in this case as well.​

Peat Moss
Peat Moss via

You can place a sheet of newspaper as you did with the indoor grow tray. This newspaper should be kept damp along with the top layer of peat moss. Once your mushrooms start showing on top, you do not need the newspaper any longer.

6. Picking portobello mushrooms

The layer below the paper can be a small growth, and waiting for at least a week longer would give you denser mushrooms. Till you harvest, the bed needs misting, especially when the weather gets hot outside. Using distilled water for misting can also be a safe way to do it.

Each spore layer should give you at least 2 batches to harvest. This lets you enjoy your mushrooms without planning your next cultivation.​

Picking the mushroom is easy as the layer of peat moss is porous and loose. This allows you to obtain your harvest without damaging the stem or any part parts. You get beautiful looking mushrooms ready for cooking.

Portobello Mushroom Growth Mistakes to Avoid

Picking poor quality spores

This is one big mistake that many users make. Unless you choose the best-rated products in the segment, there is always the risk of contamination. You never know if there are spores of other mushrooms in the batch.

Some of them might make you sick, and some might even be poisonous mushrooms. Therefore when you are growing vegetable plants of mushrooms at home, quality seeds and spores are critical.

Letting water stand in the growth bed

Some gardeners are enthusiastic in seeing the growth. Either before the mushroom pops out or after, some add too much water to the medium.

This can lead to the spores being spoilt, and your garden bed would not be giving you mushrooms any longer. To prevent this from happening, stick with misting.

If the weather is unusually warm outside, you can mist twice a day. Stagnant water is unhealthy for the spores, while constant dampness can be of great help.

Darkness to thrive

Mushrooms like this one naturally grow on tree barks and in the soil where the trees block the sunlight. Therefore you should be able to provide a dark condition for the best growth of these mushrooms.

You can take the outdoor growth of portobello as an exception to this. As you would anyway be placing a newspaper on the top layer, it helps preserve darkness for the spores to germinate.

Success rate might depend on the quality of compost and the darkness that the spores receive.

Picking too early

While every part of the mushroom is tasty, it is the bulbous head that is popular. It is the tastiest portion of the mushroom. If you would not want to pick only the stem and criminis.

You would notice the head getting rounder and bigger by the day. When this happens, your mushroom should be ready for harvest.

Once you pick the mushroom, you should not give up on the growing medium. It is likely to give a second batch from the spores you planted. Therefore wait for the harvest and then decide on ways to regrow the mushroom.

Not giving enough water

As the mushroom starts growing, you might want to fulfill its moisture needs. While compost and peat moss can both be porous, they can retain moisture well.

Therefore a little amount is all it takes to keep the medium wet at all times. Touch the peat moss and feel whether there is still some dampness left and prevent overwatering.

At the same time, you should also make sure that you are not underwatering the spot. Your mushrooms might prefer moisture for growing out through the peat moss and then growing fully in size.

A Final Word

The above are some of the common mistakes that beginners make when they are trying their luck at raising portobello mushrooms. Now that you know about these mistakes, you can easily avoid them when you bring home your spores or portobello grow kit. Here are the steps involved –

  • Buy a kit and follow the instructions for easy growth
  • If you choose to grow indoor, germinate the spores on compost and then add peat moss.
  • If you are growing outdoor, use a raised bed for optimal growth.

Portobello mushrooms are easy to handle, and there are several dishes where they can be incorporated. Given the nutritional benefits of this mushroom, you can choose to grow it either in a small batch in your kitchen or a larger one in your garden.

This gives you a great start to an endless supply of portobello mushroom for all occasions. Hope you enjoyed learning how to grow Portobello Mushrooms in your house.

Do you have any tricks to boost the growth rate? Do let us know in the comments.