Portobello Mushroom Spores

Why Portobello?

Portobello mushrooms (Agaricus bisporus) are one of the most popular cultivated mushrooms in the world known for their large size, meaty texture, and rich, earthy flavor. They’re the mature form of the common button mushroom, but when grown to full size, their broad caps (often 4–6 inches across) make them perfect for grilling, roasting, or even using as a flavorful, plant-based burger alternative.

Growing them at home gives you the satisfaction of harvesting fresh mushrooms at their peak, while also enjoying the fascinating transformation from small white pins to hearty, restaurant-quality caps.

What’s Included:

A fully colonized Portobello mushroom grow block, ready to fruit

Timeline and Growth Cycle of Portobello Mushrooms

Spore germination – begins at week 0.

Mycelium colonization – develops over 2–4 weeks as the block becomes fully white with mycelium.

Pinning stage – tiny white “pins” emerge on the surface around weeks 3–4 once the block is exposed to the right conditions.

Button stage – pins expand into small brown button mushrooms by weeks 4–5.

Mature fruiting bodies – with continued care, buttons grow into large, open Portobello caps (4–6 inches wide) around weeks 5–6.

Harvest – harvest when caps are broad and fully opened, before the gills begin to dry. Multiple flushes are possible with proper care.