Coffee grounds for plants? Isn't caffeine harmful to plants, and if so, what plants like coffee grounds?
Coffee grounds for plants? Isn’t caffeine harmful to plants, and if so, what plants like coffee grounds?
As a keen gardener, I must admit that coffee grounds are an unassuming yet exceptional ally for growing healthy, thriving plants.
While most of us give little to no thought to coffee ground leftovers, they have uses in the garden beyond simple disposal.
Can you use coffee grounds on all plants? Well, no. As it happens, not every plant loves coffee grounds.
So, which plants like coffee grounds? And how do we use this rich, aromatic brown gold to help plants thrive?
Read on; I’ll tell you all about it!
I’ll explore the wide variety of plants that love coffee grounds. I’ll also show you exactly how to use coffee grounds for the healthy growth of your leafy friends.
Table of Contents
- What’s Exactly Are Coffee Grounds?
- Why Are Coffee Grounds Good for Plants?A Rich Source of NitrogenImproves Soil Trace Mineral ContentExcellent Compost FeedstockEnhances Soil Structure and CompositionNatural Soil Amendment SupplementBoosts Soil Water RetentionBinds Harmful Chemical and Pesticide Residues
- What Plants Like Coffee Grounds?VegetablesFruiting PlantsIndoor House PlantsAcidic Soil-Loving Plants
- How to Use Coffee Grounds for PlantsMake the Best CompostLiquid Fertilizer (Coffee Grounds Tea)Mulch and Top Dressing, Anyone?Kill Harmful Garden Pests (Ugh…Slugs!)Keep Weeds At BayShoo Away Your Neighbors’ Cats
- When Coffee Grounds Don’t Work for PlantsCaffeine in Coffee Grounds Can Suppress Plant Growth Fresh Coffee Grounds Are Phytotoxic
- Final Thoughts
What’s Exactly Are Coffee Grounds? And What Do They Contain?
Apart from the obvious stuff (coffee and caffeine), fresh coffee grounds also contain the following macronutrients by volume:
Additionally, coffee grounds are rich in several plant-essential micronutrients. These include copper, calcium, iron, boron, manganese, magnesium and zinc.
While the benefits of coffee for our health are well-known, the jury’s still out on the real benefits of this medium for plant health.
Firstly, coffee grounds have a slightly acidic to neutral pH. And while this may not affect the soil’s pH much, plants that favor alkaline soil or low nitrogen conditions may not dig spent coffee grounds. See what I did there?
With that in mind, it’s essential that you check what plants like coffee ground leftovers before using them on your flowering shrubs, fruit trees or vegetable garden.
Taking the necessary precautions prevents you from messing with your soil’s acidity.
Coffee grounds may do this by adding high levels of damaging caffeine, salt and mold to your soil. These elements inhibit the growth of seedlings and young plants.
Why Are Coffee Grounds Good for Plants? 7 Good Reasons
Coffee grounds offer several benefits to some plants. But as with all things, I urge caution. Find out which plant loves coffee grounds before using this medium.
Applying too much coffee can result in poor soil conditions and have adverse effects on worms and other beneficial microbes living in the soil.
Anyway, let’s take a look at some of the most recognizable benefits of used grounds for plants.
A Rich Source of Nitrogen
One thing that all avid gardeners agree on is that coffee grounds are nitrogen-rich, containing 1-2 percent nitrogen by volume. But, you must understand that coffee grounds alone aren’t a major source of plant nutrition.
This is because the form of nitrogen in coffee grounds isn’t available to plants. Plants need soil bacteria and other microbes, such as worms, to trap and break down that nitrogen into a simpler form before they can use it.
To make them an effective nitrogen source for plant health, use spent coffee grounds together with other nitrogen sources. These include composted animal manure (chicken or goat manure is excellent!), grass clippings and alfalfa meal. Used this way, coffee grounds benefit plants as a slow-release nitrogen-rich source.
Improves Soil Trace Mineral Content
Coffee grounds can also improve soil mineral content by up to 35 percent by volume. They contain macronutrients and trace minerals essential to various plant processes, including:
Promotion of photosynthesis and fruit production
Development of fleshy leaves and vibrant flowers (nitrogen)
Strengthening of cell membranes
Development of different plant hormones and enzymes
The trace minerals in coffee ground leftovers, such as phosphorus, magnesium and calcium, increase the availability of micronutrients in soil or compost. These essential nutrients are vital for plant health and development.
Excellent Compost Feedstock
With a carbon/nitrogen ratio of approximately 20:24, fresh coffee grounds make great compost pile feedstock.
Adding fresh coffee grounds to your compost means adding premium organic matter. This will guarantee quality, nitrogen-rich compost for your potting soil, flowering shrubs or vegetables.
In addition, if you’re a coffee lover (or both a coffee lover and keen gardener like I am), you can add fresh coffee grounds to your compost pile daily. And because fresh grounds decompose quickly, you won’t have to worry about a buildup of disease-causing organisms that could affect your house or other plants.
Enhances Soil Structure and Composition
Apart from being beneficial to plant growth, coffee grounds also improve the medium in which plants grow – soil.
The degradation of used grounds produces humic compounds, which make up a majority of soil’s organic matter. This process also releases microbial glues and other organic materials. As a result, you can expect good texture and well-drained soil.
Furthermore, because coffee is organic matter, it feeds the soil’s microbes, bacteria and beneficial worms if used correctly. These microbes improve the composition and fertility of loose soil.
Natural Soil Amendment Supplement
Do you have alkaline soil but need acidic soil to grow your plants? I’m sure you’ve heard that coffee grounds can change your soil’s pH levels.
I’m sorry to burst your bubble; this is a myth! Although coffee grounds are slightly acidic, they alone won’t alter soil pH.
After brewing coffee, most of the water-soluble acid goes into that precious liquid in your coffee mug anyway. Thus, the remaining dregs have a pH range of 5.5-6.8. That’s quite close to neutral and not enough to change the pH of your soil.
Still, adding used coffee grounds to your growing medium can make a difference with acid-loving plants. Top among these are African violets, blueberries, azaleas, jade plants and hydrangeas.
Boosts Soil Water Retention
Enhancing the soil’s health, particularly its ability to retain moisture, is another useful function of coffee grounds.
Not only does this benefit plants that prefer moist soil conditions, but it also reduces the need for frequent watering. With soil water retention, you get to conserve energy while saving money. And that’s always a win in my book!
Binds Harmful Chemical and Pesticide Residues
Finally, coffee grounds are good for the environment! They trap harmful residues from chemical fertilizers and pesticides in the soil. This prevents chemicals escaping into the groundwater and polluting the surrounding environment.
If you want to do your bit for the environment, start incorporating coffee grounds into your composting and gardening routine today!
What Plants Like Coffee Grounds?
And so we get to the crux of this blog post: plants that like coffee grounds. Please keep in mind coffee grounds benefit some plants in moderate quantities. But if you overuse them, the caffeine content in coffee grounds can hinder the growth of pretty much any plant.
Leafy green plants need nitrogen for optimal health, and root crops need potassium and magnesium to thrive. Coffee is an excellent fertilizer for the following garden plants:
Fruit-producing plants enjoy a small amount of acidity in the soil to thrive. They also absorb the nitrogen and potassium in coffee grounds. This helps with photosynthesis and fruit production.
Indoor House Plants
Brewed black coffee is a good nitrogen source for the growth of green leaves and stems of indoor house plants. It can also benefit plants that love full to partial shade, as listed below.
Still, it would be best not to give them liquid coffee more than once a week.
Acidic Soil-Loving Plants
Coffee has a slightly acidic to neutral pH and is rich in nitrogen. This kills weeds, bacteria and fungi and helps the following plants thrive.
Furthermore, the leftovers from your daily cup of java contain decent amounts of magnesium and potassium. These trace minerals are essential for plant growth and health.
How to Use Coffee Grounds for Plants: 6 Effective Methods
Coffee grounds have several uses in the garden. They are a natural and relatively safe fertilizer and soil pH amendment supplement. They also keep out of the waste stream, contributing to the preservation of the environment.
However, adding coffee grounds in excess to garden soil may damage your plants’ growth. The high caffeine content can affect seed germination and hinder the development of other plants.
Here are six ways you can supplement plants that like coffee grounds:
Make the Best Compost
It would be ideal if you always composted coffee grounds before you add them to your soil or potting medium. Also, ensure that your compost heap contains no more than 20-35 percent of fresh coffee grounds by volume. Any more could make the mix too acidic, which affects the composting process.
Add other organic material, such as shredded paper, kitchen scraps, leaves and even your used coffee filter to your compositing box. These items provide an excellent carbon-rich material that forms valuable air pockets, adding oxygen to your compost.
While you may incorporate fresh coffee grounds into your compost pile, you should never use fresh coffee grounds directly in soil or your indoor plants’ potting mix. Instead, use composted coffee grounds for soil or coffee grounds tea for container plants.
Remember, too much nitrogen, water-soluble caffeine and possible mold or bacterial contamination from grounds can stunt or even inhibit seed germination and plant growth.
Liquid Fertilizer (Coffee Grounds Tea)
You can also use spent coffee grounds soaked in water on lawns and container plants that thrive in full or dappled shade. This mixture provides an excellent liquid fertilizer that gives your plants a much-needed java nutrient boost.
To make coffee grounds “tea,” fill a five-gallon bucket halfway with water and add two cups of old coffee grounds. Steep for a few hours or preferably overnight before pouring onto your garden or container plants. A once-a-week application is enough.
Oh, and don’t be tempted to drink this stuff if you’ve run out of cold brew coffee. You’ll have to trust me on that!
Mulch and Top Dressing, Anyone?
Are you stuck for mulch or top dressing options? Why not try using coffee grounds?
This gardening aid makes a fantastic mulch or top dressing, especially when mixed with other organic materials like leaf mold, newspaper, sawdust or wood chips. The key is to rake the mulch evenly over the soil to avoid compaction.
Mulch containing coffee grounds is effective at suppressing common fungal rots and wilts, such as Pythium and Fusarium. It also inhibits the growth of harmful bacteria like E. coli and Staphylococcus.
Kill Harmful Garden Pests (Ugh…Slugs!)
Are critters making your vegetable gardening a living hell? It would surprise you that the answer to getting rid of them may lie in the application of used coffee grounds.
Explore this fascinating use of coffee grounds as pest control to keep your veggie patch organic. A 1-2% solution of used coffee grounds in water is toxic to ants, snails and slugs – pests that cause immense damage to leafy plants.
To make this organic pesticide, combine nine parts water with one part strong-brewed coffee and spray all over your plants.
Oh, and coffee grounds also kill fleas, although your dog may not like it very much if you pour coffee all over them!
Keep Weeds At Bay
Need an organic weed suppressant? Look no further than coffee grounds!
Coffee grounds contain natural allelopathic properties. This means they can suppress weed growth by affecting seed germination and seedling development in other plants.
Combine grounds with organic mulch materials like wood chips and straw to make an effective weed suppressant. This mulch will minimize weed growth, especially sprouting seeds and young seedlings.
Shoo Away Your Neighbors’ Cats
If your neighbors’ cats are giving you a headache, you may have an ally in coffee grounds.
Because cats dislike the smell of coffee, add coffee grounds to your yard or garden as a natural deterrent. That’ll prevent cats from using your space as a litter box.
This way, errant felines will opt to move to a new potty site (which will help you keep the peace between you and your neighbors).
When Coffee Grounds Don’t Work for Plants: A Couple of Disadvantages
Everything has its downsides, and coffee grounds are no exception. You may face challenges using this gardening aid without knowing what plants like coffee grounds. Some of the detrimental effects of using coffee grounds on plants include:
Caffeine in Coffee Grounds Can Suppress Plant Growth
Plants, like people, react differently to caffeine. The caffeine in leftover coffee grounds stunts weeds (a positive side effect for us). But, they may also affect the growth of other plants.
Caffeine decreases the root surface area of growing plants. It does this by affecting protein development, which leads to stunted growth. It also reduces the germination percentage of seeds in some species.
Fresh Coffee Grounds Are Phytotoxic
Although used coffee grounds benefit plants that love acid soil, they can inhibit the growth of certain plants. Top among these include Italian ryegrass, asparagus fern and geraniums.
When used as mulch, fresh coffee ground leftovers are toxic. These grounds may pass on small amounts of mycotoxins and mold to the soil, harming plants.
Besides, ground coffee tends to compress, forming an impenetrable barrier across the soil surface. This can promote fungal growth while preventing airflow to the roots.
Well, ladies and gentlemen, there you have it!
Using coffee grounds on plants can benefit some, especially those that love nitrogen-rich acidic soil. Spent coffee grounds also make excellent liquid fertilizer, weed killer, cat deterrent and slug bait.
Coffee grounds may also pass on harmful fungal and bacterial contamination to soil and potting mixes. These microbes affect the growth of plants that love both acidic and alkaline soil.
Knowing what plants like coffee grounds and how to use coffee grounds in the ways I’ve covered above will insulate you from these bad effects.
I hope you’ve found this article interesting. Now I want to hear about your experiences adding coffee grounds to plants. The comments section is all yours!
What Plants Like Coffee Grounds FAQ
Not all plants like coffee grounds because they are slightly acidic, contain caffeine and are nitrogen-rich. Some plants that won’t thrive in these conditions include vegetables like Chinese mustard, grasses like Italian ryegrass, rosemary, lavender and flowering plants like geraniums.
Yes, you can sprinkle spent (but not fresh) coffee grounds in your garden. Fresh coffee grounds can introduce high levels of caffeine, mold and disease-causing microbes into the soil. Check that your plants like coffee grounds. Then, spread composted grounds in a thin layer around your garden.
Fruit and vegetable plants like blueberries, peppers and cucumbers and flowers like peace lilies and azaleas love coffee! In addition, plants that thrive in full to partial shade like African violets and jade also thrive with coffee liquid! If you decide to water your plants with coffee, make sure it’s black, with no milk, sugar or flavorings.
Coffee grounds are an excellent soil amendment medium for some potted greenery. They have a decent nitrogen content of 1-2 percent, which they release slowly into the potting soil. But, you can’t use coffee grounds on potted plants, like rosemary, lavender and geraniums, as it makes the potting mix too acidic for them.