Practical Guide to Mushroom Gardening

Please Note: The first step in growing mushrooms is having no idea where to start. Once you've accomplished that, you're ready for this guide!

There are so many ways to grow mushrooms that it can all seem overwhelming, but the truth is that mushrooms grow in the wild - it doesn't have to be complicated! In this guide, you'll learn how to grow oyster mushrooms on cold-pasteurized straw using grain spawn, an off-grid technique that doesn't require any special equipment and grows mushrooms with a rich, wild-foraged flavor. It's the easiest way to add mushrooms to your garden and builds foundational knowledge that makes more advanced techniques feel accessible.

No matter which method you're using to grow mushrooms, the entire process can usually be broken down into 5 steps: Pasteurization, Inoculation, Incubation, Fruiting, and Harvest. Understanding each step before you get started is important - mushrooms grow fast, so you'll want to plan ahead and have supplies ready.

Before You Begin

When learning how to grow mushrooms, we recommend following the "work backwards" principle and start with a few grow kits so you can learn how to fruit your mushrooms first. This gives you a chance to experiment with your environmental controls and teaches you what healthy growth looks like.

Equipment Checklist

Shroomhouse Grain Spawn
Chopped Straw 
pH Test Strips 
Mesh Bags
Hydrated Lime
Mushroom Grow Bags (Type 3B or XLS-B), 5 gallon buckets, or 16" poly tubing
55-Gallon Drum or 20+ Gallon Storage Container

Safety First: Handling Hydrated Lime

Calcium hydroxide (hydrated lime) raises the pH of water to kill contaminants, this also makes it hazardous if handled incorrectly. Avoid inhalation and skin contact, and be careful not to splash the lime water solution as it can cause burns.

Protect Yourself:
3M Full Face Respirator and Particle Filters (Protects from inhaling lime particles)
PVC-Coated Gloves (To protect hands while working with lime water)

Pasteurization: Cleaning Up Your Substrate

Pasteurizing your chopped straw reduces the number of microorganisms in it that will be competing with the mushrooms. Pasteurization leaves behind some beneficial microbes that help prevent contamination while the mycelium is growing. We use hydrated lime and water, along with a 55 gallon drum or other large container, to pasteurize chopped straw. If you don't have access to hydrated lime, you can pasteurize the straw in a hot water bath at 165°F for 90 minutes - just be sure to let it cool for 4-8 hours before inoculating it.

1. Mix the Lime Solution – Add hydrated lime to water at a ratio of 1/2 cup for every 10 gallons and mix thoroughly. Water should reach pH 11.5 or higher when tested with a pH strip.
2. Submerge the Straw – Place the straw in a mesh bag or basket and soak it in the lime water for 8–24 hours.
3. Drain to Field Capacity – Drain the straw completely for 6–8 hours or until it reaches field capacity. Test for field capacity by taking some of the straw in your hands and squeezing it as hard as you can. A few drops of water may come out, but continue draining if it creates a stream.

Why Use Hydrated Lime? This method is energy-efficient and reduces contamination risk better than hot water pasteurization, while also adding calcium, which can benefit mycelium growth.

Safely Draining Lime Water

Hydrated lime water should be drained in a safe area—preferably near alkaline-loving plants or slowly neutralized with vinegar before disposal. Consider adding a spigot for controlled drainage.

Inoculation

Step 1: Mix in Spawn

Combine Shroomhouse Grain Spawn with pasteurized straw at a 1:10 spawn-to-straw ratio by weight.

Step 2: Pack into Cropping Containers

After mixing, pack the spawned substrate into your cropping containers. We recommend food-safe 5 gallon buckets with 1/4"-1/2" holes drilled every 6-8 inches because they're stackable and reusable.

• Grow Bags – Use Type 3B (5-micron filter) for best air exchange.
• 5-Gallon Buckets – Should have aeration holes drilled for proper airflow.
• 16" Poly Tubing – Good for larger grow logs. Poke small aeration holes spaced 6-12 inches apart with a simple broad arrowhead. A utility knife works in a pinch to cut X-shaped holes instead.

Incubation

Once the straw is inoculated, it needs 10-21 days at 68–72°F to fully colonize before mushrooms start to grow. Store inside and out of direct sunlight, and use this time to set up a humid fruiting area. Keep your incubation space clean and avoid disturbing the mycelium if you decide to check on it. You'll want to monitor for contamination at this stage, keeping in mind that oyster mushrooms can usually out-compete contamination given the right conditions.

Contamination

Contamination is any microorganism in the substrate that gets in the way of your goals. It's inevitable, sometimes showing up when you’ve done everything right... but contamination doesn’t mean your mushrooms are lost! When at least 80% of your substrate is healthy mycelium, it often grows fantastic mushrooms. Move any contaminated substrate to a separate area to avoid spreading it around.

Bacteria: Patchy growth, foul smell, wet yellow spots on mushrooms. Caused by excess moisture or nitrogen, or lack of oxygen. Reduce supplementation and increase the drain time for your substrate. Ensure aeration holes are spaced evenly and temp is under 72°F.
Black Pin Mold: Thin, gray mycelium with tiny black dots. Inspect your growing area for pests, this is usually spread by gnats which can be easily controlled with yellow sticky traps. Spray the infected area with a hydrated lime solution and seal with packing tape.
Trichoderma: Green mycelium and/or dust. This contaminant spreads quickly, often going undetected until it releases its green-blue spores. If you see a green patch larger than a quarter, remove that container from your incubation or fruiting area and either allow it to fruit naturally under a tree or compost it. Trichoderma is great for your compost and plants!

After 1-2 weeks, your substrate should be finished incubating. Follow directions for fruiting as soon as you see pins!

Fruiting

Mycelium needs a humid environment with lots of fresh air and some light to stimulate healthy mushroom growth. If you're growing outdoors, this can be under a tree or shade structure with patio misters on a timer. Or just use a spray bottle on your kitchen counter!

If you're using mushroom grow bags with a filter patch, you'll want to cut an "X" or window about the size of a quarter for the mushrooms to grow through. Exposing the substrate to oxygen will trigger it to begin fruiting.

Once mushrooms start to grow, you will need to prevent them from drying out. This is typically done by maintaining a humid environment, either with heavy duty humidifiers or patio misters on a timer. A spray bottle with tap water works fine for growing small amounts of mushrooms at home. Many of the varieties we sell are able to grow outside with minimal watering if humidity is above 75% throughout the day. If the temperature is kept within the normal range for your variety, the mushrooms should double in size every day until they reach maturity after just 5-8 days.

Harvest

7-12 days after pinning begins, your mushrooms should be ready to harvest. Their color may start to fade slightly - you'll want to harvest the mushrooms just before their cap margins flatten. Harvesting sooner will give them a firmer texture, but they lose flavor and shelf life once spores are released. If you're unsure, it's always best to harvest early and save its energy for a 2nd flush!

If you're going for multiple harvests, it's important to twist the mushroom at its base when harvesting. Stems that are left behind can become points of contamination, but you can remove them with a clean knife if you're careful about minimizing damage to the healthy mycelium.

Getting More out of Your Substrate

Once you harvest your mushrooms, the mycelium will need to rest for 5-7 days before it will grow again. If you have a humid environment, you can leave the mycelium undisturbed until it begins fruiting out of the same holes. If you're using a grow bag, it's best to seal your first hole with packing tape and cut a new hole elsewhere on the bag for your 2nd flush.

Each additional flush is about 1/2 the weight of the first, so after 2-3 flushes we will compost the spent substrate. This composted straw will break down very quickly and will likely produce volunteer mushrooms if you have a dedicated pile!

Questions? I'm still working on this blog post! Please email me at Brandon@spawnshroomhouse.com with comments or suggestions. Thank you!