Coffee grounds are a great addition to your gardening toolbox as a natural fertilizer, soil improver, or to keep pests at bay. However, as with humans, not all plants like coffee! It’s also vital to use coffee grounds in a way that won’t harm your plants or the microorganisms in the soil.
The simple answer is that yes, ferns love coffee! It’s essential to know how to use it, though – it’s possible to damage your plants or reduce the soil quality by using coffee grounds incorrectly.
In this article, we’ll look at whether used coffee grounds are suitable for your ferns and how to use them to get the best results. Remember that we’re not talking about fresh coffee here – these are the waste grounds from after the brew is over.
Are coffee grounds good for Ferns?
Coffee grounds contain nutrients such as nitrogen, potassium, and phosphorus, which plants need to produce strong, healthy growth. They are also slightly acidic (pH 6.5 – 6.8), which ferns enjoy – most types love acidic soil.
Most of the acid content in ground coffee ends up in the liquid (the part that we drink!) once the coffee is brewed, so don’t expect coffee grounds to acidify your soil.
In effect, they’re pretty much pH neutral, but some types could be more acidic than others. In some experiments, used grounds have even been found to be alkaline! If you’re worried about the pH level of your soil, a pH meter can be a great help.
The mostimportant thing when using coffee grounds on your ferns is not to use too much. However you decide to use them, moderation is key!
Best Ways to Use Coffee Ground on Ferns
Composting with Coffee Grounds
Using coffee grounds in your compost bin is probably the best way to incorporate them into your garden. It’s simple – just throw your used grounds into your compost bin and use the compost as usual when it’s ready.
As well as adding nutrition, the nitrogen in the coffee grounds helps to break down the other components in the compost and ensures that the result is rich and well mixed.
However, make sure that coffee doesn’t make up more than 20% of your total compost – levels over 30% can have a detrimental effect. Good compost comprises a wide variety of green (nitrogen-rich, like coffee) and brown (carbon-rich, like leaves) materials. (Source: The University of Arizona)
Coffee Grounds as Organic Fertilizer
Coffee grounds contain about 2% nitrogen, which is the primary nutrient needed for strong, green growth. They also contain smaller amounts of other nutrients like copper, magnesium, calcium, and sugars.
A 2% nitrogen fertilizer will provide a gentle boost of nutrition to keep your ferns looking green and healthy without over-fertilizing them or burning the roots.
Mix with Mulch
Mulching with coffee grounds is a great way to easily introduce the benefits of coffee grounds to your ferns. Simply add a quarter-inch layer of grounds mixed with other organic mulching material like pine bark or leaf mold on the top of your fern’s soil.
Make sure that the coffee is evenly distributed and not in clumps. The nutrients will gradually seep into the compost below, and the coffee will inhibit pests, diseases, and weeds.
When you use coffee grounds as a mulch, it is vital not to make the layer too thick as the fine particles can form an impenetrable barrier that stops air and water from passing through, eventually starving the fern of these necessities.
Coffee Grounds as Compost Tea
If you don’t have a compost bin, a simple and effective way to use coffee grounds on your ferns is to make tea.
Quarter-fill a large glass jar with used grounds, then top up the jar with water. Leave the jar in a warm place out of direct sunlight for a couple of weeks or more if you can.
You can strain the resulting tea or not; you could even keep using the same grounds for more tea – adding fresh grounds each time.
To use your coffee compost tea, add one cup per half a gallon of water the next time you water your fern.
Add Coffee Grounds to The Potting Mix When Repotting
This is another super-simple way to use your coffee grounds. When you repot your ferns, add in a handful or two and mix them in well. They’ll add valuable nutrients to the soil, improve aeration and inhibit pests and diseases.
Because uncomposted grounds can be quite strong and can stunt the growth of young plants, never use them in large quantities and never on seedlings or young plants.
Water After Application
Probably the simplest way to use coffee grounds with your ferns is to sprinkle a small amount on the surface of the fern’s soil then water the plant thoroughly. The water will take the coffee grounds down into the soil where the plant’s roots can access them.
Ferns have a shallow root system, so this is a good method for them, but be careful not to add too much – you don’t want to encourage fungi and flies! A teaspoon or two once a month or so should do it.
Don’t Use Coffee Grounds for Seedlings!
When using coffee grounds, one crucial thing to remember is never to use them on seedlings or very young plants. In large doses, coffee inhibits growth – and even a small amount of coffee is a large dose to a tiny seedling!
To understand this mechanism, it helps to think about the coffee plant itself. Coffee plants produce caffeine in their leaves.
When these leaves drop to the ground, the caffeine is released into the soil and inhibits the growth of other plants – it’s effectively a chemical weapon against competition!
Benefits of Using Coffee Grounds
Adds Nitrogen to the Soil
As used coffee grounds contain around 2% nitrogen, they are the perfect way to enrich your soil without risking damage to your plants’ roots.
Nitrogen is essential in the soil as it provides the nutrient for ferns and provides food for the microorganisms that make it possible for plants to absorb other nutrients. The nitrogen cycle is a complex but essential process!
Nitrogen plays a vital part in leafy growth, so nitrogen is very important for your ferns to grow vigorously.
Prevents Disease Causing Agents
Used coffee grounds have been shown to inhibit the growth of several fungal diseases, including Fusarium, Pythium, and Sclerotinia and bacteria such as E. coli and Staphylococcus (more of a problem for humans than ferns!).
Using a small amount in your plant’s soil is a great way to keep these disease-causing agents away.
Anecdotally, coffee grounds are said to deter pests such as slugs and snails, as well as sap-suckers like aphids. There are a couple of possible reasons for this.
Slugs and snails aren’t fond of moving over small particles such as coffee or sand. They will do if they have to, though, so don’t count on coffee alone to keep them away from your plants!
Another possible reason why coffee can repel pests is the caffeine content. Many animals, including insects, don’t like caffeine, and there is plenty of anecdotal evidence that they will try to avoid it. In high doses, caffeine can even kill insects.
There is also some evidence that mosquitoes will avoid laying their eggs in coffee-infused areas – so it’s worth giving it a try for this alone!
Improves Soil Quality
The key to high-quality soil is a good mix of material, nutrients, and particle sizes with plenty of microorganisms to break down the organic material.
Coffee provides food for these microorganisms and, in modest quantities (less than 20%), is an excellent addition to your soil.
Improves Water Retention Capacity
The small particle size of coffee grounds means that it sticks together when it is wet. If you want to improve the water retention of very sandy soil, coffee grounds can help.
The most important thing here is to make sure the grounds are mixed in well with the rest of the material. Otherwise, they will form clumps that hold water and could lead to fungal growth or root rot.
Improves Drainage Capacity
Any kind of organic material is helpful for improving soil drainage. Drainage is key to healthy root systems – when water sits close to roots for too long, it can stop the plant from absorbing oxygen, nutrients, and even water!
A small amount of coffee grounds is helpful to improve drainage, but again, make sure you mix the grounds completely with the rest of the soil.
Keeps Pets Away
Animals don’t tend to like coffee. If you have problems with cats, dogs, or other animals invading your plants, a coffee mulch could help.
When the animals get the coffee on their paws or in their noses, it will put them off, and they’ll learn to keep away! Be careful, though – too much coffee can be toxic to dogs, so go easy.
Potential Problems with Using Coffee Grounds on Ferns
Promotes Fungal Growth
If you use a thick mulch of coffee grounds, you might soon find fungal growth all over. This fungus probably won’t harm your plant, but it is a sign that you’ve used too much coffee.
Try removing some of the coffee so that the layer is around a quarter of an inch thick. To ensure that the fungus doesn’t affect your ferns, leave a one-inch gap between the mulch and the plant’s stem.
Excess Moisture Retention
As coffee grounds increase moisture retention, you could end up with compacted, clay-like soil that holds too much water if you use too much.
This could lead to big problems for your fern, so it’s best to repot your plant and decrease the proportion of coffee in the soil by mixing in other materials like perlite.
As coffee grounds decompose, you might find that they attract pests like fungus gnats. While these are no threat to your fern, they’re not much fun to live with.
Avoid this by only using a thin mulch and by including other materials like pine bark. If you’re using coffee grounds in the soil, make sure they’re well mixed in.
Can Inhibit Growth of Your Ferns!
In large quantities, the caffeine in coffee grounds can inhibit plant growth. The best way to avoid this is by composting your grounds first or by making a compost tea.
Never use coffee grounds on seedlings or young plants, and go easy when adding coffee to your compost. It’s much easier to add more than it is to remove it!
Potential risks to soil
As coffee grounds have antibacterial and antifungal properties, it’s possible to upset the balance of microorganisms in your soil by using too much. Avoid this by using coffee grounds sparingly and ideally compost them first.
How Much Coffee Should I Add to My Ferns, And How Often?
It depends on how you’re applying it. If you’re using coffee grounds as a mulch or mixed into potting mix, once or twice a year should be fine.
If you’re using composted coffee grounds as part of your homemade compost, use it as you usually would – when repotting your plants.
You can use a coffee compost tea once every couple of weeks during the growing season, reducing to once a month in autumn. Don’t use it at all in winter. Remember to dilute the tea!
If you’re sprinkling coffee grounds on the top of the plant’s soil, don’t do it every time you make a coffee! Once a month or so will give your plant a boost without encouraging fungus and pests.
If you use them correctly, coffee grounds are great for ferns. Here are three things to remember:
- Composted coffee grounds have less potential to damage your plants and the soil. Never use more than 20% coffee in your compost!
- If you use coffee grounds for mulch, mix them with other material and keep the layer below a quarter inch.
- Never use coffee grounds or coffee compost tea for seedlings or young plants!