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- Oyster mushrooms grow well on used coffee grounds because coffee has lots of nitrogen.
- Using coffee waste for mushroom growing greatly cuts down on trash sent to landfills.
- Studies show coffee grounds help mycelium grow quickly if they are fresh and clean.
- Grounds must be used in 24 hours to stop dirt and mold from growing.
- Mixing in things like straw helps air move and makes it easier for the fungi to grow.
Every day, used coffee grounds fill up trash cans in kitchens and cafes everywhere. But could this normal waste product help you grow your own special mushrooms at home? If you are new to growing mushrooms, using coffee grounds is a cheap and green way to start. But like any way of doing things, it has good points and bad points. Let's talk about this way of growing.
Why Coffee Grounds Work for Growing Mushrooms
Coffee grounds are a good base for growing mushrooms for several reasons, both scientific and simple. When coffee beans are used to make coffee, much of the food is taken out, but not all. The grounds left behind still have a lot of carbs, oils, and, importantly for fungi, nitrogen. Nitrogen helps mycelium grow fast, especially for mushrooms that break down things, like oyster mushrooms.
And then, used coffee grounds are heated when brewed. This heat kills off most other tiny living things. This gives the mushroom spores or spawn a good start without needing hard steps to clean them. This heating is like the way big mushroom farms treat their growing stuff. This makes it easy for beginners.
And, coffee grounds have small bits and a dark color. This makes them hold water well and stay warm and wet. These two things are very important for mycelium to grow well.
From how it affects the Earth, using coffee grounds is a good example of using waste again. Instead of going to a dump and making gas that warms the planet, the grounds are used to grow food. This helps people growing at home and helps the Earth on a small scale.
Good Points About Growing Mushrooms on Coffee Grounds
Using coffee waste to grow mushrooms has many good points, especially if you are new or want to help the Earth:
- Cleaned by Heat: Making coffee heats the grounds. This kills mold spores and bad germs, so there is less chance of things growing that you don't want.
- Easy to Get: You can use coffee grounds from your own home or ask cafes nearby for theirs.
- Good for the Earth: Every pound of coffee grounds you use again means less trash and a smaller impact on the planet.
- Cheap Start: Buying things like wood pellets or sawdust costs money. Coffee waste is free and there is a lot of it.
- Simple to Start: You don't need special cookers, hard setups, or years of knowing about plants. The way is easy to understand and doesn't punish you much for mistakes.
- Fast Results: Oyster mushrooms can grow on coffee grounds quickly. You get to see results fast if you are eager.
A study by Jones et al. (2018) clearly shows the high nitrogen in coffee grounds. It says the many foods in coffee help mycelium grow strong and fast. This means you get mushrooms faster and often bigger groups of them.
Growing on coffee also helps growers learn basic skills without feeling lost. You can try things, see how things grow step by step, and learn the mushroom cycle—from putting spawn in to picking mushrooms—in a short time.
Problems to Watch For
Even with all the good points, growing mushrooms on coffee grounds is not always easy. There are problems to watch out for if you want to do well:
- High Chance of Dirt: After the coffee gets cool, tiny mold spores and germs from the air can land on it very fast. If you don't put mushroom spawn in quickly (in 24 hours), the chance of dirt growing gets much higher.
- Not Enough Air: Coffee grounds can get packed down tight. This stops air from getting through. This can make spots with no air, which is hard for mycelium that needs air. It also helps bad germs that don't need air grow. Some of these can stop growth.
- Doesn't Hold Shape Well: By themselves, grounds don't have the stringy feel of straw or sawdust. This feel helps make space for air. Not having this makes growth spotty or slow.
- Gets Bad and Too Wet: Grounds can hold too much water, mostly if not kept right. If they are too wet, slimy stuff or mold like green mold can grow.
- Only Good for a Short Time: Coffee grounds go bad fast. After a few days—even in the fridge—they don't have as much food and don't work as well.
To fix these problems, use coffee grounds that were just brewed in 24 hours. Mix them with things that give shape, like straw. And always look for signs of dirt (like bad smells or colors you don't expect).
Best Mushrooms to Grow on Coffee Grounds
Not all mushrooms can grow well in the packed, nitrogen-heavy world of coffee waste. It is best to use types that grow strong, don't give up easily, and are known for growing on different bases.
Top Types to Use:
-
Oyster Mushrooms (Pleurotus ostreatus, Pleurotus columbinus)
These are strong growers and are the best choice. They grow faster, fight off others better, and work with different conditions. They are okay with bases that are not perfect and give you thick, good-tasting caps for cooking. -
Pink Oyster (Pleurotus djamor)
These bright pink mushrooms like warm, wet places. They grow fast and are strong, which makes them very good for people starting out. They also look amazing and make your grow exciting. -
Wine Cap (Stropharia rugosoannulata)
These usually grow outside, but Wine Caps can eat mixes of coffee and other plant stuff. They are tough, don't get pests easily, and are a great extra for growers with garden space. -
Shiitake (Lentinula edodes)
Shiitake are harder to grow. They can do well on coffee grounds if mixed with sawdust from hard wood. They grow slowly and need exact water levels, so people who have grown mushrooms before should use them.
Don't Use These on Coffee Grounds:
- Lion’s Mane (Hericium erinaceus): Needs a base with lots of air that is just right. Doesn't work with the packed shape of coffee.
- Morels (Morchella spp.): These are known to be very hard to grow. They need very specific dirt conditions that you likely won't get with coffee grounds.
Using a mushroom grow kit made for coffee grounds can take away the guessing. Kits often have the right spores, the right pot, and clear steps to make up for the tricky shape of just coffee grounds.
How to Grow Mushrooms on Coffee Grounds, Step by Step
If you are new, be happy—growing mushrooms on used coffee doesn't need you to be good with plants or have costly tools. Follow these main steps for your best chance to do well:
1. Get Fresh Grounds
- Use them in 24 hours after making coffee.
- Grounds should be room warm but not too wet or dripping.
- Put in the fridge for a short time if you can't use them right away.
- Don't use grounds that are moldy, smell bad, or have strange colors.
2. Mix in Mushroom Spawn
- Use 1 part spawn to 5 parts coffee grounds.
- Break spawn into small pieces so the mycelium can touch more coffee.
- Think about adding something extra (10–20% cut straw or sawdust from hard wood) to make the shape better and let air in.
3. Put in Your Pot
- Use a clean plastic bag (like a ziplock or grow bag) or a bucket with 3–5 small holes for air.
- Gently press the mix down, but don't make it too wet.
- Keep it 55–65% wet—it should feel wet but not soaking.
4. Mycelium Growing Stage
- Keep the pot in a dark place that stays the same temperature (best: 65–75°F or 18–24°C).
- Mycelium should show up in 7–14 days.
- Wait until the coffee grounds are mostly white with mycelium before going to the next step.
5. Making Mushrooms Stage
- Give the mix with mycelium some soft light and fresh air.
- Cut 2–4 holes in the pot so mushroom pins can come out.
- Spray lightly with water 2–3 times a day to keep it 85–95% wet.
- Mushrooms will show up in 5–7 days and can get twice as big every day!
If you can, use a mushroom grow kit. These often have spawn that is already growing on a clean mix. This can help you do well and make fewer mistakes at the start.
What You Need: List of Things for Beginners
Having the right things makes what you are doing easier and the result much better. Here is what you need:
Needed Things
- 5–6 cups of fresh used coffee grounds
- Oyster mushroom spawn (best for people starting)
- Pot: plastic bag, bucket, or tub with air holes or openings
- Spray bottle (to spray water daily)
- Clean sharp knife or scissors (to cut holes in bag or pick mushrooms)
Things That Can Help
- Gloves (to help keep things clean)
- Tape/labels (to write dates, keep track of groups)
- Hygrometer (to check how wet the air is)
- Straw or sawdust (to add for more mushrooms)
If you plan to grow more, you might also want to start checking how acid the mix is (pH) and the temperature all the time. Big growers often aim for pH 5.5–6.5 for the mycelium to work best.
Picking the Right Spawn for Beginners
When you start growing mushrooms, "spawn" is what carries the fungal mycelium. It is usually grain, sawdust, or small wood pieces. Choosing the right spawn is very important for a good grow.
Why Oyster Spawn is Best:
- Grows Fast: Can grow all over in as little as 14 days if conditions are right.
- Fights Dirt: Good at fighting off other things, especially when using bases like coffee that are not fully clean.
- Works in Different Places: They grow well in many temperatures and water levels in the air.
Common Types of Oyster Spawn:
- Pearl Oyster (Pleurotus ostreatus): Good for room temperatures (65–75°F).
- Blue Oyster (Pleurotus columbinus): Does best when it's colder (50–65°F).
- Pink Oyster (Pleurotus djamor): Loves warm, tropical heat (75–85°F) and looks very bright.
You can buy spawn online or from shops that sell mushroom supplies. Look for spawn from trusted places—it should be clean, fresh, and put in a good bag. For your first time, a mushroom grow kit that has the base, spawn, and pot might be the easiest choice.
Fixing Problems: How to Solve Common Issues
Even the best setups can have problems. Here is how to fix things that often go wrong:
| Problem | Why It Happens | How to Fix It |
|---|---|---|
| Grows slow or not at all | Too cold, old spawn, or dry base | Make the area warm (65–75°F), spray water to make it wet again, make sure spawn is fresh |
| Green Mold or Black Spots | Dirty coffee, not clean enough work area | Scrape off the bad part (if small), start again (if bad all over) |
| Feels slimy | Too much water or no air | Spray less often, mix the stuff up, add dry material to help water go out |
| Mushrooms not showing up | Air not wet enough or not enough air flow | Spray water more often (2–3 times a day), check how wet the air is (85–95%) |
Getting More Mushrooms & Not Getting Dirt
Things you can do to make your first grow even better:
- Make it Stronger: Mix in straw, torn up cardboard, or sawdust from hard wood to make the mix less packed and give it more food.
- Work Clean: Always clean tools and surfaces with alcohol (70% isopropyl alcohol) before touching the materials.
- Control Heat: Keep the heat steady—sudden changes can make mycelium slow down or kill spores.
- Wet Air Tents: Make simple tents to keep air wet. Use a clear box or plastic bag with holes. This keeps things wet without too much spraying.
Coffee Grounds vs. Other Bases
Coffee grounds are great for people starting out. But people who have grown before often use other things after they learn the basics.
| Base | How Much Food | How Long It Lasts | Easy to Use |
|---|---|---|---|
| Coffee Grounds | High (for a short time) | Low (goes bad fast) | Very Easy |
| Straw | Medium | Medium | Easy (needs heating) |
| Hardwood Sawdust | High | High | Medium hard |
| Coconut Coir | Medium | High | Easy, holds water well |
| Manure Mix | Very High | Medium–Low (high chance of dirt) | Only for experienced |
Questions Often Asked by Beginners
Are mushrooms grown on coffee grounds okay to eat?
Yes! They are safe to eat—there is no caffeine in the mushrooms themselves.
Can I heat the grounds again to be extra safe?
You can heat them again in a microwave or oven for 10–15 minutes to clean them. But using fresh grounds is better.
Do mushroom grow kits have coffee grounds in them?
Usually no. But some kits for beginners have coffee mixed in after heating. Always check before you buy.
How long does it take to grow?
From putting the spawn in to picking the first time takes about 3–4 weeks with oyster mushrooms.
So—Good Idea or Bad Idea?
What's the answer? Growing mushrooms on coffee grounds is a good idea—especially if you are new to growing mushrooms or want to try it in a green and cheap way. If you make sure to:
- Use clean, fresh grounds
- Pick mushrooms that grow well like oysters
- Watch for dirt
- Add other things when you can
...then you will have a system that works and gives good results. And with things like grow kits that are ready to use and help from groups, it has never been easier to start.
Something Special in Mushrooms and Coffee
There is something special about changing coffee from yesterday into food for tomorrow. This way of doing things not only makes less trash. It also lets you enter the world of growing things again using fungi. Learn more, get tasty mushrooms, and feel good about using coffee waste.
Ready to make mushrooms grow from your own kitchen? Look at our mushroom grow kits or order fresh oyster spawn today and start your indoor fungi farm!
