Step 1: Cut the Bag — Opening Your Mushroom Grow Kit

The first step in fruiting your mushroom grow kit is creating an opening for the mushrooms to grow through. Your kit arrives as a fully colonized substrate block sealed inside a filter-patch bag. The mycelium inside has already done the hard work of colonizing the substrate — now it needs an exit point where it can sense fresh air and humidity changes, which trigger the transition from vegetative growth to mushroom production.

How to Cut the Opening

Using a clean knife or scissors, cut a 2-3 inch X-shaped slit through the plastic bag on the side where the substrate appears most densely colonized. You will recognize dense colonization by the thick, bright white mycelium visible through the bag — it should look solid and uniform rather than thin or patchy. If the entire bag looks evenly colonized, cut the opening on the broadest flat side of the block.

Before cutting, wipe your knife or scissors with isopropyl alcohol (70% concentration works best) and let it dry for a few seconds. This simple sanitation step prevents introducing contaminants through the fresh opening. You do not need to sterilize the tool with flame or autoclave — a quick alcohol wipe is sufficient for this step since the colonized substrate has a strong immune defense from the established mycelium.

How Big Should the Opening Be?

A 2-3 inch X-shaped cut is ideal for most species. This size gives the mushrooms enough room to form a cluster and grow outward without being so large that the substrate dries out quickly. Some growers prefer to cut a single straight slit rather than an X — this works fine for aggressive fruiters like oyster mushrooms but may restrict pinning for species that form larger individual fruit bodies like lion’s mane.

For lion’s mane specifically, many growers cut a slightly larger opening (3-4 inches) or even remove a small section of bag entirely, because lion’s mane forms a single large fruiting body that needs room to expand. For oyster mushrooms, which produce clusters of smaller caps, the standard X-cut is perfect.

Alternative: Removing the Block from the Bag

Some experienced growers prefer to remove the fully colonized block from the bag entirely and place it on a wire rack or inside a fruiting chamber. This exposes more surface area and can result in mushrooms pinning from multiple locations rather than just the single opening. However, this approach requires a higher-humidity environment (a humidity tent, Martha tent, or shotgun fruiting chamber) because the exposed block will dry out much faster than one still partially enclosed in its bag.

If you are a beginner, we recommend keeping the block in the bag and using the X-cut method. It is simpler, requires less humidity management, and produces excellent results for all species in our grow kit lineup. Once you are comfortable with the basics of fruiting, you can experiment with full-block exposure on future grows.

What to Expect After Cutting

After cutting the opening, you may not see any visible changes for the first few days. The mycelium needs time to sense the environmental shift — the change in gas exchange, humidity, and light at the opening. Within 3-7 days, you should start to see small bumps or knots forming at the cut edges. These are called primordia, and they are the earliest stage of mushroom development. Once primordia appear, mushroom growth accelerates rapidly. Move on to Step 2: Mist to keep those developing mushrooms properly hydrated.