Growing Portobello Mushrooms at Home Plant AmericaIf you want to grow Portobello mushrooms of the Agaricaceae family at home, you’ll find that it is an easy and fun process as long as you give it the right conditions. It is an awesome idea as you get to learn how the world of Agaricus genus fungi works while you also get rewarded with a sweet delicacy when you harvest your mushrooms.

Read this article to learn the two tried and tested techniques in growing your Portobello mushrooms.

How To Grow Portobello Mushrooms: Growing Your Mushrooms By Yourself

Doing all the work and growing your Portobello mushrooms from their spores by yourself is not as difficult as you may think. Just follow the steps below:

1. Gather Everything That You Need

Since you do not have a mushroom kit, you should gather the following items to start your Portobello mushrooms:

  • Mushroom spores: You can easily find portobello mushroom spores in online stores or any gardening shop near you. The spores are very tiny and do not look like they are alive (just like seeds).
  • Nails, wood and hammer: You will be building a substrate base for a planting bed.
  • Compost: Manure-based compost is preferable as it is the most nutritious. However, any finished compost will do.
  • Thermometer: You will need this to test the temperature of the substrate and atmosphere so that you can decide if your Portobello mushrooms can grow there or not.
  • Rubber gloves: Growing mushrooms can be a dirty job, so you need to protect your hands.
  • Peat moss: Mushroom growers use peat moss to maintain moisture for the growing mycelium cells.
  • Newspaper: Mushroom growers also use newspapers to maintain consistent moisture in the substrate.

When you have gathered everything that you need, move on to the next step.

2. Build a Planting Bed for the Substrate

You should build a box that resembles a cuboid. It should be at least 8 inches deep and 6 inches wide. This box is where you will keep your substrate and also grow your mushrooms.

Take note that if you can find a similar product made of plastic or other materials that do not degrade, it is better than the one made of wood as wood can degrade quickly when growing mushrooms.

3. Pour Your Compost Into the Bed

You should pour compost into the planting bed you just constructed so that at most 6 inches of it is covered. Do not worry about the smell of compost because if the compost is a finished product, it should not release any foul smell.

You should keep at least 2 inches of the upper part of your planting bed free so that you can add peat moss and a newspaper sheet later.

4. Sterilize the Substrate

Sterilization is very important when growing mushrooms. If you do not sterilize the substrate and bed, other microbes such as harmful fungi and bacteria can compete with your Portobello mushrooms for nutrients and space. You must sterilize all your working equipment when growing mushrooms.

Sterilize the Substrate Plant America

Two common methods you can use to sterilize your substrate and bed are:

  • Bake the Bed: You should insert the entire bed (almost filled with compost) into a large metal barrel or pot, pour in some water, and then boil the water for about 30 minutes to 1 hour. When done properly, this technique is the fastest and easiest way to sterilize substrate for growing mushrooms.
  • Use the Solarization method: To use a more natural method of sterilization, cover the bed with cardboard and then cover everything with a black plastic wrap. Place it under the sun for at least two weeks. The heat of the sun will kill harmful bacteria and other unwanted organisms in the substrate.

Sterilizing is necessary especially if you are growing your mushrooms indoors, so do not skip this step. Take note that what you are sterilizing are your working materials such as the substrate and bed. Do not sterilize your mushroom spores.

5. Keep the Substrate in a Dark and Cool Place 

Portobello mushrooms love their environment to be cool, dark and humid. You should keep the substrate in a place that is around 50 to 70 degrees Fahrenheit. Recommended places where you can keep the substrate are in the corner of a shed or room (if you are growing Portobello mushrooms indoors) or under a tree (for outdoor mushroom cultivation).

Make sure that you do not expose the mushrooms to direct sunlight as they will not grow properly due to quick dehydration.

6. Monitor the Temperature and Other Climatic Factors

Your preferred location should not go above 70 degrees Fahrenheit during the day. It should also not go lower than 50 degrees Fahrenheit at night. Always pay attention to the temperature because the growth of mushrooms depends heavily on the right temperature.

When growing your mushrooms outdoors, rain is okay. Mushrooms grow best in a moist environment, so you should not cover the substrate from the rain. For indoor mushrooms, you will have to water the growing Portobello mycelium cells regularly.

As for humidity, Portobello mushrooms love a very humid environment. The humidity should be slightly above 75 percent. You can achieve this by misting your mushrooms regularly.

7. Introduce Your Portobello Mushroom Spores

Now that you have everything in place and the atmospheric condition is just right, it is time to introduce the Portobello mushroom spores. Follow the steps below:

Portobello Mushroom Spores Plant America

  1. Remove the plastic and cardboard: Do you remember the plastic wrap and cardboard that you covered the substrate with earlier? Remove them if you haven’t already. You can dispose of them in the waste bin.
  2. Mix in your Portobello spores: You should mix the mushroom spores into at most 1 inch of the compost substrate. Do not mix them deeper so that you can quickly monitor your mushroom growth. Also, do not mix them too shallowly so that the cells can quickly start to grow.
  3. Press the compost when done: When you have carefully mixed in the spores, use your hands (remember to wear your gloves) to press down the compost so that it is not as loose as it was after mixing.

Now the journey of growing your mushrooms is getting more exciting. Move on to the next step.

8. Cover the Substrate With Peat Moss and Newspaper

When you have mixed in the mushroom’s spores, you should cover the substrate with at most 1 inch of peat moss.

The peat moss will help retain the moisture of the substrate so that it does not dry out. Without peat moss, your mushrooms may not survive in that substrate as it can get dry quickly.

You should also cover the layer of peat moss with a single sheet of newspaper. The purpose of the newspaper is to maintain the optimum temperature and moisture in the substrate while your mushroom mycelia cells are growing.

9. Mist the Newspaper Daily

Using a spray bottle, you should mist the newspaper covering your mushrooms regularly. You should mist it once a day if you are growing your mushrooms indoors or twice a day when growing them outdoors as they can dry out easily outside.

Always monitor the newspaper. Do not allow any part of the newspaper to become dry, and always mist the newspaper when you notice it starting to dry up. Continue to mist the newspaper until you are ready to reveal your mushroom primordia.

10. Remove the Newspaper When You See Mushroom Primordia

After two weeks, you should see some tiny mushroom primordia when you remove the newspaper. The primordia looks just like the edible mushrooms we know but way smaller. Seeing primordia in the substrate means that you are successful in growing your mushrooms even though they are not mature yet.

If you do not see the primordia, you should mist the substrate and cover it for an extra week. The primordia should emerge by then. If they do not emerge, you should check your spores and determine if something is wrong with them.

Remember that you should not sterilize your mushroom spores.

11. Continue Misting the Mushrooms

Do not stop misting your mushroom primordia. Mist for about 10 more days, two to three times daily according to the humidity of the room. Don’t stop misting them even when they are mature and ready for harvest.

12. Collect Mature Portobello Mushrooms

You can identify mature Portobello mushrooms with the diameter of their caps. Your mushrooms are ready for harvest when their caps are 1.6 to 2.4 inches in diameter. If you harvest the mushrooms too quickly, it means that you will be harvesting brown criminis instead of Portobello mushrooms.

Collect Mature Portobello Mushrooms Plant America

You should wait until the edges of your Portobello mushroom caps are flat and not curled before you harvest them. You can harvest the mushrooms by digging and pulling them off. Select a specific head, brush off the substrate around it, and pull it from its base.

Harvest all your mature Portobello mushrooms just like this, wash them and store them in a refrigerator until you are ready to consume them.

13. Repeat the Process From Step Eight

Guess what — even though you have harvested some Portobello mushrooms, you are not done with them just yet. You only harvested the first batch as more mushrooms will come.

Go back to step eight of this process by covering the substrate with a single sheet of newspaper and misting it. In less than two weeks, a new set of Portobello heads will appear.

You can continue to enrich the substrate by adding more compost or rotted manure for a steady harvest of mushrooms. Take note that seasonal changes in temperature and humidity can halt the development of mushroom heads, so you should enjoy your Portobello mushrooms while you still can. If you want to add some plants, make sure that they like the mushroom compost.

This process is easy, right? Now let us discuss how to grow Portobello mushrooms using an easier process.

Growing Your Mushrooms With a Growing Kit

Growing mushrooms when you already have a growing kit is super fun and easy. This time around, you will be given Portobello mushroom spawn instead of spores as producers make Portobello mushroom spawn and not spores.

Follow the steps below to grow your Portobello mushrooms with a growing kit:

1. Sterilize the Trays and Substrate

When you get the growing kit, you need to sterilize the substrate. Most growing kits come with trays instead of a planting bed, so you need to sterilize the trays as well.

Sterilize the substrate and trays by baking them. Keep them in a hot oven for at least 30 minutes to eliminate the chances of harmful bacteria or fungi competing with your Portobello mushrooms.

2. Fill Trays With Substrate

The substrate should cover at least 2 inches of the tray. The deeper the tray, the better. Adding more substrate also means more Portobello mushrooms for you as they will grow more heads in a larger surface area.

Growing Portobello Mushrooms With a Growing Kit Plant America

Also, there will be enough nutrients to last for two to three sets of Portobello mushrooms.

3. Introduce the Portobello Spawns

Pour in half (½) a cup of mushroom spawn on the surface of the substrate. Using a sterilized spoon, carefully mix the spawn into the substrate. Mix them so that they are uniformly spread across the substrate in the tray.

Doing so will ensure that your mushroom mycelia cells will spread quickly and that you will have mushroom heads across the whole tray.

4. Place the Tray in a Cool and Dark Place

Most mushroom kits are best kept indoors because their substrate is more nutritious than compost and easily attracts microbes. You should keep your tray on a shelf in a room without direct sunlight.

The temperature of the room should stay at around 70 degrees Fahrenheit in the daytime and 50 degrees Fahrenheit at night.

As an extra tip, you should limit your movements in the room because opening doors regularly can expose your mushrooms to the wind and draft.

5. Cover the Tray With Newspaper

You should cover the Portobello mushroom tray full of the substrate with a newspaper. This is important so that the substrate does not get dry quickly. Newspapers also help to maintain the temperature and humidity in the substrate.

If the mushroom kit came with peat moss, you do not need to add extra as the substrate can serve that purpose as well.

6. Mist Newspaper for Two Weeks

Continue to mist your newspaper until you get a spawn run, which can happen in about two weeks. Never allow any part of the newspaper to become dry. The newspaper should be consistently moist as you can use it to monitor the moisture of the substrate.

Take note that you should not overwater your mushrooms as overwatering can also kill them. Keep the substrate consistently moist. If you can, you should perforate little drainage holes below the trays.

7. Mist the Primordium

When you have your Portobello primordium, mist them regularly until they are mature and ready for harvest. This can take up to 10 days. Do not allow them to dry out.

8. Harvest Your Mature Mushrooms

It is easy to harvest your mature Portobello mushrooms when you grow them in a tray. You just need to brush off the substrate around a mature head and then pluck it out. You can pluck it by twisting and pulling. You can also use a knife, but you need to cut it from the base.

You can identify mature Portobello mushrooms by their flat edges as opposed to the curly edges of younger ones.

9. Repeat Process From Step Five

Guess what — you do not need to introduce a new set of mushroom spawns to get more Portobello mushrooms.

All you need to do is to cover the substrate with fresh newspaper after harvesting your first batch of mushrooms. Don’t worry, the mycelia cells inside the substrate will produce more heads for you.


Easy technique, right? Which of the two major methods of growing Portobello mushrooms would you like to try?

Useful Terms

Throughout the article, you may have come across some of these terms that you are unfamiliar with:

  • Mycelium: Portobello mushroom mycelium (pl. mycelia) is the mushroom cell that grows inside the substrate. They are like the roots of a plant.
  • Primordium: This is an immature mushroom head that just formed.
  • Spawn Run: Spawn run happens when your mycelia have spread across the surface of your substrate.
  • Decomposition: As decomposers, mushrooms (i.e. fungi) get their nutrients from decomposing a nutrient-rich substrate.
  • Fruiting: Fruiting refers to the development of a mature mushroom head.

Remember their meanings as you learn about and grow your Portobello mushrooms.

5/5 - (16 votes)