Greenhouse Gardening - How to Grow Portobello Mushrooms?

Greenhouse Gardening - How to Grow Portobello Mushrooms?

Apr 11, 2017 0 comments

Portobello mushrooms or oversized crimini are brown crimini mushrooms that have attained full maturity. They are native to the grasslands in North America and Europe. Portobello mushrooms are very rich in Vitamin B and phosphorus. They are easy to grow inside a greenhouse. Here is how:


  • Start by setting up growing trays inside the greenhouse. These trays should be 8 inches deep and between 6 and 8 inches long. Fill the trays with about 6 inches of compost, peat moss, and mushroom spores.
  • Cover the trays with newspaper to keep it moist and dark until the whitish mycelium appears on the surface of the compost.
  • Ensure the temperature inside the greenhouse ranges between 65 and 70 degrees Fahrenheit.
  • When you spot the mycelium, add about 2 inches of damp peat moss over the existing substrate and then cover this with a fresh layer of newspaper.
  • You should then reduce the temperature inside the greenhouse down to 55 degrees Fahrenheit.
  • After about two weeks, remove the layer of the newspaper once the little white heads start emerging from the compost.

Tips and tricks

  • Portobello mushrooms take about a week to mature from the moment the little head emerges from compost. As such, do not rush to harvest.
  • Mushrooms require a lot of water. But, ensure the substrate is merely damp and not "wet". 

Common problems

  • You should watch out for dark-winged fungus gnats and scuttle flies, which may lay eggs on the compost. The larvae that hatch from these eggs damage mushrooms during all their stages of growth.
  • Pseudomonas bacteria is a problem too. 

Watering requirements

  • Portobello mushrooms require quite a bit of water so ensure you water the trays with between 5 and 7 inches of water every two days. 

Soil requirements

  • Portobello mushrooms thrive in nutrient-rich compost. The ideal substrate to use is straw mixed with horse manure.

Lighting requirements

Mushrooms do not have chlorophyll; they do not need light. During spawning, the greenhouse needs to be as dark as possible. However, they require dim light when they start forming heads. During this stage, light from a fluorescent lamp or indirect sunlight is sufficient. Greenhouse kits that can offer this kind of lighting are ideal. 


Harvest Portobello mushrooms when the heads attain a diameter of about 4 and 6 inches. Do this by picking the mature mushrooms off the substrate while holding the stem.

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