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Writer's pictureMatthew Gauger

Multiple Mushroom Flushes

Updated: Aug 8

What is a "mushroom flush"


Mushroom cultivation can be both a fascinating hobby and a profitable venture, but getting those mushrooms to flush more than once can be a bit of an art. A "flush" refers to a wave of mushrooms that sprout from the substrate, and with the right care and attention, you can coax your fungi to produce multiple flushes, meaning more mushrooms for your efforts. Let’s dive into some strategies to help you maximize your yield.



The Mushroom Cycle

First, it’s essential to understand the basics of the mushroom life cycle. It all starts with spores, which, under the right conditions, germinate and form mycelium—a web-like network that feeds on the substrate you've prepared. This mycelium eventually forms tiny pinheads, or primordia, which are the first signs of mushrooms. These grow into full-sized mushrooms that can be harvested in what’s known as the first flush. After this initial burst of growth, the mycelium needs some time to recover before it can produce another flush. The key to getting multiple flushes lies in how well you treat the mycelium during this recovery phase and beyond.


Mushroom Substrate

The quality of the substrate you use plays a huge role in determining whether you’ll see multiple flushes. The substrate is the material on which the mycelium grows, and it needs to be rich in nutrients to sustain the mycelium over several flushes. Common choices include straw, hardwood sawdust, and composted manure, each offering different benefits depending on the type of mushroom you’re growing. The substrate needs to be pasteurized or sterilized to kill off any competing organisms, which would otherwise consume the nutrients meant for your mushrooms.


Mushroom Conditions

Once you’ve prepared your substrate, hydration is key. The substrate should be moist but not waterlogged, as too much moisture can lead to contamination. A good rule of thumb is to aim for a moisture content of around 60-65%, where the substrate feels damp to the touch but doesn’t drip water when squeezed. This balance ensures that the mycelium has enough water to grow but isn’t drowning in it.


Environmental conditions play a crucial role in encouraging multiple flushes. Mushrooms are quite sensitive to their surroundings, so maintaining the right temperature and humidity is essential. Different species of mushrooms have their own specific temperature ranges for optimal growth. For instance, oyster mushrooms prefer a range between 60-75°F, while shiitake mushrooms might need a cooler environment after colonization to trigger fruiting. Keeping an eye on the temperature and adjusting it as needed can make a big difference in how many flushes you get.


Humidity is equally important, especially during the fruiting phase. Mushrooms thrive in high humidity—think 80-95%—but after the first flush, you might want to reduce humidity slightly before increasing it again. This fluctuation can signal the mycelium to start producing another flush. Maintaining this balance can be tricky, so using a misting system or humidifier can help keep the environment consistent.


Another factor to consider is fresh air exchange. Mycelium needs oxygen to grow, but during fruiting, too much carbon dioxide can inhibit mushroom development. Ensuring that your grow area is well-ventilated while maintaining high humidity levels is a delicate balance, especially after the first flush when the mycelium might be more vulnerable to contamination.


Contaminants

Speaking of contamination, it’s something you’ll need to be vigilant about, particularly as the substrate ages. Older substrates become more susceptible to molds and bacteria, which can ruin your crop. Keeping the growing environment clean and using a diluted hydrogen peroxide solution to mist the substrate can help reduce the risk of contamination.


Getting More Flushes From Your Spawn

After harvesting the first flush, your mycelium needs a bit of TLC to prepare for the next round. This involves allowing it to rest for a few days to a week, giving it time to recover. Once rested, you’ll want to rehydrate the substrate to encourage further growth. This can be done by soaking the substrate block in water for several hours, then allowing it to drain thoroughly. Ensuring the substrate doesn’t stay waterlogged is crucial because too much water can lead to contamination and stunt future growth.


If you’re growing different types of mushrooms, you’ll need to tailor your approach depending on the species. For example, oyster mushrooms are relatively easy to encourage into multiple flushes because of their aggressive growth. They respond well to rehydration and can produce up to four flushes with proper care. Shiitake mushrooms, on the other hand, often require a more extended resting period after the first flush and benefit from being grown on hardwood logs or sawdust blocks. After their initial flush, allowing the substrate to dry out slightly before re-soaking can mimic natural seasonal changes, encouraging another flush.


One method that can help in sustaining multiple flushes is applying a casing layer to your substrate. This layer, made from materials like peat moss or vermiculite, helps retain moisture and protects the mycelium. For some species, like button mushrooms or shiitake, a casing layer can also stimulate pinning, the stage where the tiny mushroom primordia form. It’s important to keep this casing layer moist, but not too wet, throughout the growth cycle to provide a microclimate that promotes healthy mushroom development.


Harvesting

When it comes to harvesting, the technique you use can influence whether the substrate will continue to produce. Harvest your mushrooms by gently twisting or cutting them at the base. This prevents unnecessary damage to the surrounding mycelium, which needs to stay healthy to produce more flushes. After harvesting, remove any leftover stem bases or mushroom debris from the substrate. Leaving this material behind can rot and create an environment ripe for contamination, which can hinder future growth.


Finally, while it’s possible to achieve multiple flushes, it’s important to have realistic expectations. Each subsequent flush usually yields fewer mushrooms than the first, as the substrate’s nutrients become depleted. However, with careful attention to rehydration, environmental conditions, and contamination control, you can maximize your substrate’s potential and enjoy multiple waves of fresh mushrooms.


Cultivating mushrooms for multiple flushes is as much an art as it is a science. By understanding the life cycle of your fungi and providing the right care at each stage, you can extend the productivity of your substrate and enjoy a more bountiful harvest. Whether you’re growing mushrooms for personal use or as a commercial endeavor, the satisfaction of coaxing out that second, third, or even fourth flush is well worth the effort.

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