Mushroom growing, when to harvest champignons?

Question

I am having a small experimental box with brown champignons in my basement. It already had two great waves of mushrooms, but it seems I waited too long because they all were opened up already.

When I watched the day before, I harvested a few big ones and left the smaller ones to grow a little more - next day all of them were opened and didn't have the typical champignon shape anymore.

I have also noticed, that my mushroom stems seem to be quite long in relation to the mushroom head (e.g. 10cm/4inches) in average.

Champignons are grown on straw substrate covered with clay-based soil (all ready and prepped by the shipper) The room is pretty dry but the box is covered with a perforated plastic sheet to contain more moisture. Room temperature is 10-14 degrees, it's pretty dark most of the day (just enough light to walk around when eyes are conditioned)

So here my questions:

• How do I know when to harvest a champignon?
• When I harvest, should I cut the stem or just rip/screw it out?
• Do I have to harvest all at once, no matter what size?
• Anything I can do to grow them bigger heads smaller stems?

The mushroom box

First harvest

Just 1-2 days later

Answer 1

How do I know when to harvest a champignon?

You can harvest it once it has formed a cap. When small it's called a button mushroom, and at its largest size it's called a portobello mushroom. If the ends of the mushroom are curling upwards, it's a little late.

When I harvest, should I cut the stem or just rip/screw it out?

Twist them out. They suggest not using a knife as it might infect the stem with bacteria. If a large amount of stem is left you can cover it with the casing material to stop it getting infected.

Do I have to harvest all at once, no matter what size?

Most people harvest them when they're the size that they want. Sometimes when you twist them out you get all sizes which is not avoidable.

Anything I can do to grow them bigger heads smaller stems?

The growers cut the stems off as they collect them. If you want a larger mushroom, you'll need a larger mycelial mass. The growers have huge beds but the kits are too small to produce huge mushrooms.

I would have waited longer before harvesting myself so that you have a bigger cap.

Answer 2

Those are fine-looking mushrooms!

The key for mushrooms "like from the store" (in Germany) is to harvest when they are not yet fully mature. This means that the velum, the thin skin at the underside of the cap, is still closed. A mature mushroom will have a flatter cap with exposed gills, ready to release the spores. And mushrooms mature quickly once they have reached the mature size: What was a round "button" one day will have started to open on the next and be probably fully stretched the day after that. If you look at your pictures, the first ones have already started to open. This is the latest time to harvest as “buttons”, you can expect those to fully expand overnight.

So the correct time to harvest for your purposes is when the mushroom is nice and plump, but not yet open. And yes, this may mean you get to harvest a few mushrooms every day, just let the tiny ones grow a bit more.
Not all caps will reach the same size, you may assume that commercially available mushrooms have been sorted a bit and the “not so perfect ones” used otherwise, like for most produce.

When you harvest, gently twist the stem out. Cutting is not recommended, for remaining stem parts can encourage mould and a knife can bring unwanted bacteria unless you are very diligent in cleaning it. For the same reason you should remove “aborts”, i.e. tiny heads that don’t develop before they can harbor mould. If a hole remains, you can use a clean (!) knife or other tools to gently push the substrate over it.

And if you had a few caps mature too quickly, I suggest you do some research on recipes using the larger heads, they are wonderful fried whole and used similar to meat on sandwiches, for example. Note that you might have to check for recipes from the UK, the US or similar, in Germany the larger heads are rarely available, at least not in supermarkets.

Your mushrooms in the pictures are too close. At this stage you will need to pick the bigger ones and thin them out a bit. All the growing energy is being drained out of the compost. That will then allow the others to get bigger. Pick your brown mushrooms when they are approximately 2" to 2-1/2" in diameter. Remember to maintain 85 to 90% humidity, Temperature of 22 degrees Celsius.