Are Coffee Grounds Good or Bad for Orchids?
Thinking of throwing some coffee grounds into your orchid potting mix? While coffee grounds can be used successfully as compost material, what about as a soil additive? In this article, gardening expert Melissa Strauss examines if it's a good idea to use coffee grounds with your orchids, or if it's just another gardening tip you should skip.
For a moment there, every coffee shop was doing it. Selling bags of used coffee grounds with the promise that they would help bring new life and vigor to your garden. Perhaps unsurprisingly for coffee enthusiasts, this was not an empty promise. Quite the opposite, in fact. Coffee grounds provide a ton of nitrogen to plants once they are broken down in the soil they are added to.
Orchids, however, present a bit of a conundrum in this department. It’s true that orchids love good fertilizing. They are big fans of nitrogen, which helps them to produce new, healthy, robust growth, and ultimately, flowers. But these tropical flowers require a very specific type of potting medium, and this complicates the theory a bit.
Let’s discuss the use of coffee grounds as fertilizer and decide whether coffee grounds are a valuable tool in raising orchids. The all-important question is, are coffee grounds good for orchids? In addition, are there any specific drawbacks, or can they cause damage to an orchid. Let’s jump in.
The Short Answer
Because of the type of soil orchids are planted in, coffee grounds do not break down and the nitrogen and additional nutrients they contain are not released for the orchid’s use. Terrestrial orchids are the exception to this. The soil they are planted in can make the nutrients in coffee grounds bioavailable to the plant. For all other orchid types, adding coffee grounds to orchid potting mix can be detrimental to the health of the plant.
The Long Answer
Coffee grounds are known to be a great source of nitrogen, and other nutrients, for plants. When applied to the soil, the grounds break down through a process which involves nitrifying bacteria that resides within the soil. Through this process, the grounds release the natural plant fuels that they contain.
The issue regarding orchids is that epiphytic orchids are not planted in standard soil. Since most orchids are epiphytic, they have specific needs where potting medium is concerned.
How it Works
Coffee grounds are a rich source of nitrogen, phosphorus and potassium, all favorites of orchids, and most other plants, really. They also contain a number of other nutrients which can be beneficial to plants. This means that some gardeners view coffee grounds as an inexpensive fertilizer.
The caveat in using coffee grounds to fertilize comes down to the way these nutrients are made available to plants. They require nitrifying bacteria (earthworms work as well) to make the nutrients they contain available for a plant to utilize. This is especially true with nitrogen.
This bacterium only exists in places where there is a significant amount of ammonia in the soil. This is the reason that they are a great addition to your compost.
I highly recommend tossing your daily caffeine castoffs into your compost bin. If, like myself and millions of others, you start your day with a cup of Joe, it’s a completely free way to enrich your compost with lots of wonderful nutrients that your plants will love.
For a more thorough explanation of how the process works, check out this study from Washington State University on the value of using coffee grounds in the garden.
To someone who is unfamiliar with the way these tropical flowers grow, this seems like a no brainer. Coffee grinds are full or nutrients, add them to your plant’s soil, save on fertilizer and see lots of growth. If you have been caring for orchids for any span of time, you might already have guessed why coffee grounds are not as effective for orchids as they are for other plants.
Why it Doesn’t Work
The problem with orchids is that they are very picky about their drainage situation. In nature, their roots are fully exposed to the elements. So, in captivity, they really need to have excellent air circulation and drainage to maintain their integrity. Their roots will rot very quickly in regular potting soil because it holds too much water.
A standard potting mix for orchids contains about 60% bark, mixed with a combination of charcoal, perlite, sponge rock and sphagnum moss.
Because ammonia is not present in bark mixes in any significant amount, and since earthworms are not either, it stands to reason that coffee grounds sprinkled on top of orchid bark will not break down. Therefore, the nutrients will not be available for the plant to absorb.
What’s the Harm?
Now that we know why coffee grounds are not beneficial as fertilizer or soil amendment, let’s look into whether they can actually cause harm to your prized epiphytes. There are a couple of ways that they can be detrimental to the health of the plant.
The first issue is that coffee grounds are small particles that can get caught up in orchid bark. They can clog the flow of water and leading to orchid root rot because they hold water where it would typically drain freely.
In addition, the acidity of coffee can cause the potting mix to break down faster. This creates a similar issue, as smaller particles of any medium tend to mean more water retention.
While neither of these issues means instant death for an orchid, they both lead to root rot, which is the number one killer of indoor orchids. If you’ve been adding grounds to your potting mix, this might be the time to repot using fresh potting mix.
Experts recommend using a balanced fertilizer on your orchids. Plant-specific fertilizers work well, but any standard balanced fertilizer will work. Orchids like to be fertilized weekly during their growing season, and once every 3 weeks during their off season.
If you are curious about some of the homemade fertilizing methods, there are a few that will definitely increase the health of your plant, without causing the harm that coffee grounds can.
For example, an orchid-friendly Epsom salt solution can be a great addition to your care routine. A solution of 2 tablespoons of Epsom salt dissolved in 1 gallon of water will provide plenty of magnesium.
This can help lead to better blooms, especially orchid plants grown indoors. Banana peel tea is also a great option, albeit slightly controversial. Before you toss those peels in the compost, soak them in water, out of direct sunlight, for 3 days. Then use the water as fertilizer.
While coffee grounds are a fantastic addition to your compost, the nature of their decomposition is not effective for most orchids. In addition, they cause rapid decomposition of orchid potting bark, creating an environment that is primed for root rot. It is best to save those grounds for other plants.