It figures – You’ve only just learned that all those coffee grounds you’ve been throwing out daily are good for the garden.
So you began emptying used K-cups and setting aside your used coffee filters with the grounds intact so that you could compost them or add them directly to your azaleas or blueberries.
But when it was time to use the grounds, you discovered they’d gone moldy!
Was all that effort wasted, or can you still use the moldy coffee grounds?
Can You Use Moldy Coffee Grounds In The Garden?
The simple answer is yes – and no.
Not all molds are created equal, and there are some important factors to consider before you attempt to use the grounds on your plants.
The Myth Of Mold
Those out there will tell you that coffee grounds and other composting materials must be destroyed the moment you see any signs of fungal growth or mold.
Now think about that for a moment.
The whole purpose of composting is to decompose organic material and carbon to create fertilizer.
This is literally the same process used by Mother Nature herself, with mold and fungi having evolved specifically to aid in this task.
Now, there are some types of mold or fungi that you don’t want in your garden or compost pile, but others are absolutely essential.
So next time you hear someone tell you to throw compostable materials out because they’re moldy, take a moment to think about colors.
Identifying Several Common Types Of Coffee Mold Based on Color
That’s right. You need to consider color when your compostable materials show signs of mold.
Coffee grounds are a great example of color-based identification in action, so let’s look at some common coffee mold colors and what they mean.
That blue-green mold is likely a safe strain of Aspergillus or Penicillium. You’ve no doubt seen these two molds growing on bread.
While penicillin is derived from Penicillium and can be a life-saving medication, Aspergillus can be dangerous, with some species being quite harmful. In contrast, others are used in creating medications or even sake.
But when it comes to your garden or compost pile, these blue-green molds are perfectly safe and may even provide some minor benefit to your plants.
Brown To Black Mold
When you see these colors, it’s bad news every time.
There are five common molds with these colors:
- Alternaria alternata
- Aspergillus niger
- Cladosporium herbarum
- Cladosporium sphaerospermum
- Stachybotrys chartarum
The mold is toxic to you and your plants in all of these cases.
Thus, if you happen to see mold on your coffee grounds that are black or brown, dispose of them immediately and give your hands and anything the grounds have touched an excellent scrub down.
While there are a few green molds, the most likely suspect is Trichoderma spp. This is one of the best molds to see growing on your coffee grounds, as it’s perfectly safe for your plants.
In fact, it’s considered beneficial on an agricultural level. So if you see green mold on your coffee grounds, don’t hesitate to add them to your garden or compost pile!
Like black or brown mold, this is one you definitely don’t want to see.
The most common culprit is fusarium, a nasty piece of work that can infect plants and do a lot of damage.
While it’s not common to see pinkish or reddish mold on coffee grounds, you should immediately discard any showing these colors and sterilize the area in which the grounds were being stored.
White, feathery mold on your coffee grounds is most likely Aspergillus, one of the most common molds affecting coffee grounds.
As with the blue-green strains, the white strain won’t harm your garden.
However, it’s usually better to throw this lot into the compost pile where it’ll do the most good.
So Why Use Moldy Coffee Grounds?
Coffee grounds (especially when the filter is shredded and included as a carbon source) are a great nitrogen source and a natural pest control agent.
They also have a lot of acidities, making them perfect for azaleas and other acid-loving plants.
However, like all organic materials, coffee grounds need to decompose to release their beneficial components into the soil.
When you use coffee grounds with a safe type of mold (blue-green, green, or white in color), it speeds up this decomposition process, allowing your plants to reap the benefits much more quickly.
Regarding the compost pile, coffee grounds are a major draw for beneficial nematodes, which help break down the other composting materials.
So next time you plan to add your coffee grounds to the compost pile or directly onto the soil but find mold, don’t just throw it away.
Take a moment to look at the mold’s color and use that to decide whether to use the grounds or dispose of them.
Remember, you should always wear gloves when handling mold, and it’s usually good to have a face mask on to avoid inhaling any spores that might lead to respiratory issues down the road.