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How to Grow Portobello Mushrooms: Grow Guide

Portobello mushrooms are among the most popular culinary mushrooms used worldwide in both restaurants and home kitchens. These dark, meaty mushrooms may be pretty expensive at the grocery store, but the good news is that it’s quite easy to grow Portobello mushrooms yourself to have a never-ending supply right at home.

To grow Portobello mushrooms start with a sterilized compost known as the mushroom substrate. After you’ve gotten the raised bed and substrate set up you can then add the mushroom spores. To continue growing, the mushrooms will need to be sprayed with distilled water periodically. Lastly, you just need to harvest and enjoy the mushrooms.

Growing mushrooms might seem difficult if you’ve never done it before, but once you’ve successfully harvested your first batch, you’ll be itching to branch out into new mushroom types. Keep reading to learn more about how to grow portobello mushrooms from start to finish.

Supplies Needed to Grow Portobello Mushrooms

The supplies needed to grow portobello mushrooms are fairly simple, but you’ll need to make sure you have them all to grow mushrooms successfully. Mushrooms are more delicate than growing vegetables or flowers. Portobello mushrooms require a sterile growing substrate and maintenance throughout the mushroom’s growth cycle.

Here is a list of the basic supplies needed for growing portobello mushrooms:

  • Raised bed (four feet long, four feet wide, and eight inches deep): It’s best to use new raised beds for mushrooms rather than using a raised bed that has previously held other plants since this can lead to plant-borne pathogens that may damage the mushrooms.
  • Seasoned manure-based compost: Compost is one of the best growing mediums for mushrooms because it provides the necessary organic materials that mushrooms need to feed on as they grow. Using sterilized compost (link to Amazon) is better than using unsterilized manure since it can help prevent disease.
  • Peat moss: Peat moss (link to Amazon) is used to provide a layer of protection over the mushroom spores once they’ve appeared. Peat moss retains moisture well but is also well-ventilated to prevent the mushroom spores from becoming stagnant.
  • Cardboard: Cardboard is used to place over the raised bed before adding the mushroom spores to help sterilize the ground through solar radiation. Placing down cardboard will also help kill off any dormant weeds which may compete with the mushrooms for nourishment.
  • Black thermal plastic: Black thermal plastic is laid over the raised bed along with cardboard to prepare the beds for mushroom spores. Black landscaping plastic is the easiest type to use and can be cut to size for any raised bed.
  • Portobello mushroom spores: Portobello mushroom spores can be purchased online from many different vendors. Some portobello mushroom spores come as part of a full mushroom growing kit (link to Amazon) that can help take a lot of the guesswork out of growing mushrooms for culinary use.
  • Newspaper: Newspaper is used to help prevent the mushrooms from being exposed to the elements as they grow. Recycled newspaper or kraft paper rolls can also be used for this purpose if a sterile medium is preferred.
  • Spray bottle: A spray bottle is needed for misting the mushrooms as they grow. Using a hose, sprinkler, or watering can on growing mushrooms can be too disruptive to the growing spores and may reduce the number of mushrooms you eventually harvest.

Growing portobello mushrooms in your backyard isn’t hard as long as you have the right tools for the job. Once you have the above materials gathered up, you’re reading to set up your portobello mushroom bed.

Setting Up a Raised Bed for Portobello Mushrooms

After you’ve built a raised bed for your portobello mushrooms, the first thing you should do is fill it up with six inches of compost. In mushroom horticulture, this is known as the mushroom substrate. (Source: University of Florida)

You can purchase either sterilized compost or you can use an old microwave to sterilize compost yourself. Compost can be sterilized in a microwave at two to two and a half minutes on high power for every pound of compost sterilized. (Source: Primrose)

When the bed is filled with compost, it should be layered first with cardboard and then with black thermal plastic. The plastic will prevent the cardboard from becoming waterlogged and will also help to heat up the soil underneath. Once the bed is covered with plastic, it should be left to sit for two weeks.

Here’s a quick video showing how to grow mushrooms in a container if you didn’t want to use a raised bed. This is similar to using a mushroom growing kit (link to Amazon) which have become a popular way to grow mushrooms.

Growing Portobello Mushrooms: Two Weeks In

At the beginning of the third week, the cardboard and plastic should be removed. At this point mushroom spores should be added to the top of the compost in a one-inch layer and then mixed loosely into the top inch of the compost. (Source: Gardening Know How)

After mixing spores into the top of the raised bed, wait for a few days until you see evidence of the spores spreading, which can be seen as a fine web-like white growth along the top of the compost. If this growth is seen, it’s time to cover the bed with two inches of peat moss before topping it off with newspaper. Moisten the newspaper with a spray bottle of distilled water.

Maintaining Portobello Mushrooms During Growth

Once portobello mushrooms are established, they should generally require less maintenance than vegetables or flowers since you don’t need to weed them. The growing mushrooms should be misted with distilled water regularly over the top of the newspaper, being sure to keep it slightly damp at all times.

The mushrooms should be grown for at least 10-12 days before attempting to harvest them. However, the longer the mushrooms are left to grow, the larger they will become.

Harvesting Portobello Mushrooms

After ten days or more, the portobello mushrooms should be large enough to harvest. Portobello mushrooms are best harvested when the mushroom caps are 1.6 to 2.4 inches across in diameter. (Source: Wikihow) To harvest the mushrooms, perform the following:

  • Dig the mushrooms completely out of the compost substrate.
  • Gently brush off as much dirt from the mushrooms as possible with a soft-bristled brush or slightly damp paper towel. Use sterile gloves when harvesting to prevent transferring contaminants to the remaining mushrooms as they grow.

Harvested mushrooms can be stored in a brown paper bag to keep them fresh for seven to ten days in the refrigerator.

Tips for Growing Portobello Mushrooms

Even though the process of growing portobello mushrooms is fairly straightforward, there are still some important growing tips that can be gleaned from the experience of people who have grown and harvested their own mushrooms before you. Here are a few hints to help you get the most out of your first portobello mushroom growing experience:

  • Keep the mushroom bed moist. Mushrooms require consistent humidity in order to grow successfully, so making sure the newspaper over the growing mushrooms remains damp throughout the growth process will improve your results.
  • Fence the mushroom bed off. Squirrels, dogs, cats, and other pests can dig around and disturb unprotected mushroom beds, so be sure to put up a short fence or some other barrier around the beds once the cardboard and plastic are removed to keep animals away from your harvest.
  • Be careful digging the mushrooms up. It’s easy to accidentally disturb the surrounding mushrooms when you harvest one, so be gentle as you harvest the first mushrooms to ensure the stable growth of the rest. (Source: Kentucky State University)

Growing mushrooms isn’t difficult, but it does require gardeners to stay vigilant about growing conditions. As long as you’re willing to commit to tending the bed every day, you should end up with dozens of mushrooms in less than a month.

Growing Portobello Mushrooms Is Great for Beginners

If you want to get into growing your own mushrooms, it’s hard to find an easier starter mushroom than the portobello. Follow the above grow guide to get started harvesting some portobellos of your own!

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