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How to Grow Portobello Mushrooms

How to Grow Portobello Mushrooms – The Best Way to Grow

How to Grow Portobello Mushrooms

Are you wondering how to grow portobello mushrooms at home? Is it worth the trouble? In this article we’ll share the best way to grow portobello mushrooms at home.

If you’ve ever tasted a savory Portobello mushroom, air fried to perfection, you know just how delightful these fungi can be. They offer a delicious, meaty texture, and a wonderful, earthy flavor that makes them a favorite in many dishes.

What are Portobello Mushrooms?

Before we delve into the details of growing these fabulous fungi, let’s understand them a bit better. Portobello mushrooms are essentially mature Cremini, or ‘button’, mushrooms. The main difference between a button mushroom and a Portobello comes down to age. Button mushrooms are harvested when they’re young and small, while Portobellos are left to grow until they’re fully mature and their caps have expanded completely.

Growing Portobello Mushrooms at Home

You might be wondering, how long does it take to grow these delectable mushrooms? Typically, Portobello mushrooms take around 4-6 weeks to grow to full maturity from the start of the cultivation process. This includes the time for the mycelium to colonize the growing medium and for the actual mushrooms to sprout and mature.

Optimal Conditions for Growing Portobellos

Indoor Vs. Outdoor Growing

Whether you’re considering growing Portobello mushrooms outside or inside, both options are viable. However, they require different care and maintenance routines.

Indoor Growing

With indoor growing, you have more control over the growing conditions, like temperature, light, and humidity, making it ideal for beginners. A dark, draft-free space, with a consistent temperature of about 55-70°F and humidity levels around 95%, is perfect for growing Portobello mushrooms.

Gather Supplies

You’ll need mushroom spawn (also known as mycelium), a growing medium (such as compost or a mixture of manure and nutrients), a container or growing bed, a spray bottle, and a clean, dark space with controlled temperature and humidity.

Prepare the Growing Medium

If using compost, pasteurize it by heating it to around 160°F (71°C) for at least an hour. This helps eliminate competing organisms. If using a straw and manure mixture, soak the straw in water overnight and mix it with sterilized manure. Or you can buy a sterilized grow bag to avoid all of these steps.

Fill the container or growing bed: Fill your container or growing bed with the prepared growing medium. Ensure that it’s evenly distributed and packed lightly.

Plant the Spawn

Break apart the mushroom spawn into small pieces and spread them evenly on top of the growing medium. Gently press them into the surface without burying them completely.

Cover the Spawn

Spread a thin layer (about 1/4 inch) of pasteurized soil, peat moss or coco coir over the spawn. This layer helps maintain moisture and protects the spawn.

Create the Right Environment

Place the container or growing bed in a dark space, such as a basement or a closet. Maintain a consistent temperature between 60-70°F (15-21°C) and high humidity levels (around 80-90%). You can use a humidifier or mist the growing area with water from a spray bottle to maintain humidity.

Growing Portobello Mushrooms at Home

Provide Proper Air Circulation

Mushrooms need fresh air, but avoid direct drafts. Set up a fan in the room on a low setting to ensure gentle airflow. Drafts may result in contaminants entering your grow space.

Mushrooms release carbon dioxide during respiration, which can accumulate in their environment. High carbon dioxide levels can hinder mushroom growth and health. Fresh air exchange helps remove the excess carbon dioxide, maintaining optimal growing conditions.

Additionally, proper ventilation regulates temperature and humidity, which are vital for mushroom growth. Mushrooms thrive within specific temperature and humidity ranges, and adequate air circulation prevents the buildup of condensation.

Furthermore, fresh air exchange reduces the risk of contamination by molds, bacteria, and other harmful microorganisms. It improves air circulation, prevents stagnant air, and removes volatile organic compounds and odors.

Maintain Moisture

Mist the growing medium regularly with water to keep it moist but not overly wet. Avoid direct watering as it may disrupt the mycelium.

Monitor and Wait

Check the growing medium for any signs of contamination or unusual growth. Within a few weeks, you should start seeing mycelium spreading across the surface. Devices that monitor pH and humidity can make your life a lot easier.

Induce Fruiting

After the mycelium has fully colonized the growing medium (white web-like network), induce fruiting by exposing the container or bed to indirect light. Maintain a temperature around 55-60°F (13-16°C). Mist the mushrooms and their surroundings daily to maintain humidity.


Portobello mushrooms are typically harvested when the caps reach about 4-6 inches (10-15 cm) in diameter. Use a sharp knife or scissors to cut the mushroom at the base of the stem or carefully twist them off. If you keep your substrate moist, you may get second and third flushes of mushrooms!

Outdoor Growing

Outdoor growing is a bit more challenging as it requires a shady, moist area with good air circulation. It also calls for a little more attention due to changing weather conditions. Still, the effort can pay off beautifully with a fresh, organic harvest of Portobello mushrooms from your garden.

Growing portobello mushrooms outdoors requires attention to site selection, soil preparation, spawning, and maintenance.

Site selection is crucial for successful portobello mushroom cultivation. Choose a location that offers partial shade, as these mushrooms prefer indirect sunlight. Ensure the site has good drainage to avoid waterlogging, which can lead to fungal diseases. Clear the area of any debris or vegetation to create a clean growing space.

Soil Preparation

Prepare the soil by loosening it with a garden fork or tiller to improve aeration. Incorporate organic matter like compost or well-rotted manure to enrich the soil with nutrients. Aim for a soil pH between 6 and 7, which is ideal for mushroom growth.

Obtain portobello mushroom spawn from a reputable supplier or start your own by purchasing a mushroom-growing kit. The spawn contains the mycelium, the vegetative part of the fungus. Create a mixture of compost and straw or wood chips, ensuring it holds together when squeezed. Spread the mushroom spawn evenly over the prepared soil, gently pressing it into the surface.

Portobello Substrate

Maintaining Your Outdoor Mushroom Bed

Maintain the mushroom bed by keeping it consistently moist without overwatering. Mulch the bed with straw or wood chips to retain moisture and suppress weed growth. Provide a temperature range of 60-70°F (15-21°C) and keep humidity levels around 80% as the mushrooms develop. Harvest the portobello mushrooms when their caps reach a desired size of approximately 4-6 inches (10-15 cm) in diameter. Carefully twist or cut the mushrooms at the base, being mindful not to disturb the surrounding soil.

For more precise guidance tailored to your specific region and climate, consult local resources or experienced growers. With proper care and attention, you can enjoy a bountiful harvest of flavorful portobello mushrooms grown right in your outdoor space.

Propagation: Spores Vs. Liquid Culture Syringe

Starting from Spores

Starting with Portobello mushroom spores can be a bit tricky as it requires sterile conditions to avoid contamination. Spores are generally collected from a mature mushroom cap and then used to inoculate a growth medium.

Using a Liquid Culture Syringe

On the other hand, a liquid culture syringe, containing mycelium suspended in a nutrient-rich liquid, can offer a quicker start. This method can expedite the colonization process and potentially lead to a faster harvest.

In a liquid culture syringe, mycelium have already begun to form. They can be injected safely into sterile grain bags, lowering the chances of contamination as a result. You can also see if the specimen is viable and free of contamination prior to using.

Obtaining Portobello Mushroom Spores

One might wonder, how do you get Portobello mushroom spores? You can purchase them online from reputable suppliers, or you can collect them yourself from a mature Portobello mushroom. However, the latter requires a sterile environment to prevent contamination.

Can You Grow Portobello Mushrooms from Store-Bought Mushrooms?

Technically, yes, you can grow Portobello mushrooms from store-bought ones. However, the success rate tends to be quite low due to potential contamination. Furthermore, commercial mushrooms are often treated to inhibit spore production, which makes propagation more challenging.

Substrates and Grow Media for Portobello Mushrooms

Choosing the right substrate or grow medium is crucial for the successful cultivation of Portobello mushrooms. They thrive best in a mixture of composted manure or straw, gypsum, and a casing layer of peat moss and lime. This combination provides a nutrient-rich environment that promotes healthy mycelial growth and ultimately, a bountiful mushroom harvest.

Commercial Cultivation of Portobello Mushrooms

Growing Portobello mushrooms commercially for profit requires careful planning and significant initial investment. Besides the large space needed, commercial cultivation also involves equipment for controlling environmental conditions and maintaining sterile conditions, and hiring experienced personnel. However, the demand for these nutritious, tasty mushrooms is consistently high, making it a potentially profitable venture.


There you have it, a comprehensive guide to growing Portobello mushrooms at home, whether you’re a hobbyist or an aspiring commercial grower. The journey might be a bit intricate and requires patience, but the reward of harvesting your own fresh, organic Portobello mushrooms is certainly worth the effort. Happy mushroom growing!

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