How to Grow Portobello Mushrooms

Co-authored by Maggie Moran

Last Updated: January 24, 2022

Fresh portobello mushrooms are easier to grow than you may think. To make the process as simple as possible, purchase a growing kit. Otherwise, assemble a planting bed and plant portobello spores in it. Whether you choose to grow the mushrooms indoors or outdoors, keep the soil damp and at the appropriate temperature. Soon, you will have tasty mushrooms to add to a hamburger or chop up into a salad.

Part 1

Part 1 of 3:

Building the Planting Bed

1
Build a tray frame out of scrap wood. Pick up some scrap wood from a lumberyard or purchase boards from a home improvement store. The frame should be about 8 in (20 cm) deep and at least 6 in (15 cm) long. Nail the wood together to form the bed.^{[1]
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- Instead of assembling a tray, purchase a mushroom-growing kit from a gardening store or online. It includes all the components you need for growing mushrooms.
2
Fill the bed with manure-based compost. Purchase a bag of compost from a gardening center, then pour it into the bed until it is 6 in (15 cm) deep. Avoid filling up the tray so you have space to mix the soil and add peat moss later.^{[2]
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- The manure mixed in is dried, so it shouldn’t stink up your house. However, you may try other organic compost products in place of manure-based compost.
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3
Cover the bed with black plastic when growing portobellos outdoors. To sterilize the soil, lay a piece of cardboard over the compost. Cover the cardboard with a single layer of black plastic sheeting, which you can find at a general store or home improvement store. Make sure it’s tight inside the bed and won’t get blown away by the wind.^{[3]
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- If you chose to grow your portobellos indoors, sterilizing the soil likely won't be necessary. You can still do it if you wish to ensure that your mushrooms grow big and healthy.
4
Leave the bed in the sunlight for 2 weeks when growing outdoors. Leave the plastic in place and let the bed sit out in the sun. The sunlight will pass through the plastic and cardboard, clearing the compost of harmful bacteria that can damage the mushrooms.^{[4]
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Part 2

Part 2 of 3:

Protecting and Watering the Bed

1
Place the bed in a dark room to grow portobellos indoors. Put the tray in a dark corner of a shed, closet, basement, or another suitable area. The dark room should be kept between 50 to 70 °F (10 to 21 °C). Because you’re working indoors, the temperature most likely won’t need to be adjusted.
2
Move the bed to a climate-controlled area for outdoors growing. For the mushrooms to grow, the temperature needs to be no higher than 70 °F (21 °C) in the daytime and no lower than 50 °F (10 °C) at night. If the temperature goes beyond this, you may need to move the bed to a safer location, such as in shade or indoors.^{[5]
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- A dark area, such as in the shade of a tree, also helps, but it’s most important to get the temperature right.
- You can monitor the soil by placing a soil thermometer in the bed.
- Mushrooms do well in water, so rain falling on your planting bed is okay.
3
Mix the mushroom spores into the compost. Mushroom spores can be purchased online and may also be found at some gardening stores. Once you have them, put on a pair of rubber gloves. Sprinkle the spores onto the compost, then gently mix them in about 1 in (2.5 cm). Press down on the compost when you’re finished.^{[6]
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- First, remove the plastic and cardboard if you used it to sterilize the soil.
4
Cover the compost with peat moss and newspaper. Get some peat moss from a garden center or home improvement store. Spread a 1 in (2.5 cm) layer over the compost. Then spread a single layer of newspaper over the peat moss.^{[7]
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5
Mist the newspaper daily to keep it moist. Use a spray bottle at least once a day to keep the newspaper wet. If it looks dry, spray it to keep up the humidity level in the bed. Mushrooms thrive in damp environments, so it’s unlikely that you’ll supply too much water by misting.
- If you’re growing outdoors, increase misting to twice a day to ensure the bed doesn’t dry out.

Part 3

Part 3 of 3:

Harvesting the Portobellos

1
Remove the newspaper in 2 weeks if the mushrooms are growing. After the 2 weeks are up, lift up the newspaper. Look for tiny, white heads coming out of the peat moss. If they’re there, leave the newspaper off.^{[8]
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- You may see white streaks in the soil, which means the mushrooms are taking root. Leave the newspaper in place and continue misting for another week.
2
Continue misting the mushrooms as they grow. Mist the peat moss every day so water continues to drip into the bed. After about 10 days, the mushrooms will be fully-grown, although you can harvest the mushrooms sooner if you wish.
3
Dig out the portobellos when the caps have fully unfurled. Portobellos reach their peak when the mushroom caps are about 4 to 6 cm (1.6 to 2.4 in) in diameter. Dig them out of the compost by hand, then clean them off with a damp paper towel and store them in a brown paper bag in the refrigerator.^{[9]
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- Harvesting the mushrooms early means you’ll be eating brown criminis instead of portobellos. Wait until the edges of the caps are flat instead of curled.
4
Repeat moistening the compost until new mushrooms form. Keep your tray with compost intact for now. Continue moistening the compost daily, then add a new layer of newspaper once white streaks form again. By following the same steps, you will usually get 2 or 3 batches of mushrooms out of 1 tray.^{[10]
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Expert Q&A
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Question

How do you get spores from mushrooms?

Maggie Moran
Home & Garden Specialist
Maggie Moran is a Professional Gardener in Pennsylvania.

Maggie Moran

Home & Garden Specialist

Expert Answer

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The process works the best with gilled mushrooms. To create a spore print, cut off the stalk of a fresh mushroom and lay the gill side down in a glass container and cover. Allow 6-12 hours for spores to be released and collect them from the glass.
Question

Can you grow portobello mushrooms at home?

Maggie Moran
Home & Garden Specialist
Maggie Moran is a Professional Gardener in Pennsylvania.

Maggie Moran

Home & Garden Specialist

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Yes, actually mushrooms grow the best inside. Obtain mushroom spores and a growing tray. Fill the tray with compost materials and sprinkle approx 2 cups of spores on the top. Keep the tray moist and in the dark.
Question

What are the best mushrooms to grow?

Maggie Moran
Home & Garden Specialist
Maggie Moran is a Professional Gardener in Pennsylvania.

Maggie Moran

Home & Garden Specialist

Expert Answer

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While many types of mushrooms are relatively easy to grow on your own, button mushrooms are widely accepted as a wonderful beginning plant.