Coffee grounds were already used in grandmother's time to loosen the structure of potted plant soil and to fertilize the plants. Today more is known about the properties of the supposed waste product. As a supplementary fertilizer it is suitable for most plants.
Which plants like coffee grounds as fertilizer?
Tomatoes and other plants that prefer moderately acidic soil, coffee is just the thing
Coffee grounds are a good fertilizer for plants that grow in a moderately acidic to almost neutral environment. You can use the free fertilizer in the vegetable patch or work it into the substrate under hedges and bushes. Some houseplants can be treated with an aqueous extract of coffee grounds. Seedlings do not tolerate coffee fertilization well because they tend to shoot quickly due to the excessive nitrogen supply.
| preferred pH value | Examples: good NPK fertilizers | Are coffee grounds suitable? | |
|---|---|---|---|
| Orchids | 5, 5 to 6, 0 | 10-8-10 | yes, if plants grow in substrate |
| Roses | 5, 5 to 7, 0 | 7-5-8 | yes |
| hydrangeas | 4, 0 to 5, 5 (to 6, 0) | 7-3-6 | conditionally, as a supplement |
| Tomatoes | 6, 5 to 7, 0 | 7-3-10 | yes, as a supplement |
| Peppers | 6, 2 to 7, 0 | 6-6-8 | yes, as a supplement |
| Geraniums | 5, 5 to 6, 0 | 3-7-10 | conditional, very economical use |
| Cucumbers | 5, 6 to 6, 5 | 4-5-8 | yes |
| Blueberries | 4, 0 to 5, 0 | 3-3-5 | conditional, sparing use |
| Lemon tree | 5, 5 to 6, 5 | 14-7-14 | yes, as a long-term fertilizer |
Since a plant's nutrient requirements change over the course of the growing season, fertilizers with different NPK ratios are necessary depending on the season. Nitrogen-rich fertilizers such as coffee grounds are particularly useful for many plants in spring as they promote the growth of leaves and shoots.
Can coffee grounds be used without restrictions?
Coffee grounds are less acidic than you think
The myth that coffee grounds should only be used for plants in acidic soils is widespread. In fact, the pH value of the coffee residue is not particularly acidic and can lead to deficiency symptoms in real ericaceous plants such as rhododendrons. The plant likes values around 4.5 and tends to have dark green leaf veins if the pH is too high. Plants that rely on calcareous soil can tolerate small amounts of coffee grounds. This includes zucchini, which thrives at a neutral pH of 7.0.
Coffee grounds usually have a very slightly acidic pH value and are not suitable for ericaceous plants.
Coffee grounds for flowers
Whether flowers should be provided with natural fertilizer depends on the respective species. As with vegetable plants, there are consuming flowers and those that thrive better in poor locations. In general, flowering plants should be fertilized sparingly with coffee grounds because the NPK ratio is not optimal. These plants develop more splendidly when they receive less nitrogen and more phosphorus. These plants include bluebells, boxwood, carnations and bulbous plants such as daffodils and tulips.
Summer flowers benefit from coffee grounds:
- have a high nutrient requirement, so coffee grounds are not sufficient as fertilizer
- Better to mix and administer three parts of coffee grounds and one part of flower fertilizer
- Soil organisms convert coffee grounds more quickly and produce humus
- improved soil properties support the growth of summer flowers
Herbs
Most herbs are undemanding and thrive even without additional fertilization. However, herbs in partially shaded locations have different needs than sun-loving plants. Mediterranean herbs rely on poor soils and can become diseased or die if they are oversupplied with nutrients. Other culinary herbs are nutrient-depleting and require additional fertilization.
Garden and potted herbs are so different:
- Herbs from poor soils: lavender, rosemary or savory do not tolerate coffee grounds
- lime-loving herbs: coffee fertilizer is unsuitable for oregano, sage or borage
- nutrient-depleting herbs: lemon verbena or chives can be fertilized with coffee
Use coffee grounds
The basic requirement for fertilizing with coffee grounds is preparatory storage. If you use it wet, mold will quickly form. The powder doesn't go bad if it gets moldy. However, it must then be sterilized before use so that the mold does not spread into the soil.
Drying
Pour the leftovers from the coffee filter into a wide container in which you can spread the material loosely. The bottom of a mini greenhouse is ideal for drying. Place the container on a sunny windowsill and mix the powder daily. You can use a fork to break up any lumps.
Another option is drying in the oven at 50 to 100 degrees Celsius. After about 30 minutes the substrate is dry. You can also spread coffee grounds on a plate and microwave them on medium power for five minutes.
Apply
When you plant young plants in the garden, you can add a few teaspoons of coffee grounds to the planting hole. When repotting, provide your potted plants with a mixture of potting soil and coffee grounds in small quantities. For plants in coarse substrate, we recommend watering with an aqueous extract of coffee grounds.
To do this, add the fine-crumb powder to water and let the mixture steep for a few days. Be careful not to allow too much coffee powder to accumulate on the surface of the substrate. If this is the case, you should work it into the soil with a small rake.
- Lanzgeitfertilizer: sprinkle coffee grounds on the bed once or twice a year
- Instant fertilizer: if necessary, brew coffee grounds again and pour when cool
- Composting: Coffee grounds should not be more than 20 percent of the compost volume
How often and how much coffee grounds?
As far as the dosage is concerned, you should experiment yourself. Depending on the type of coffee, the ingredients can vary and the fertilizing effect differs depending on your plants and environmental conditions. Start with small amounts and see how your plants react. You can then slowly increase the dose until an optimal condition is achieved.
Guidelines for orientation:
- Coffee grounds can be used outdoors four times a year
- Work the contents of a coffee filter (approx. 30 grams) into the substrate per fertilization
- Fertilize houseplants with coffee powder in winter and spring
- Two teaspoons (about four to eight grams) of powder are sufficient per plant
Ingredients and effects in the garden
The fact that coffee grounds are valuable for rhododendrons, peonies and ferns is primarily due to the ingredients and less to the pH value. This is subject to fluctuations, which are influenced by coffee powder, but are not permanently sealed. In order for the plants to benefit from the valuable ingredients, you have to incorporate the residues into the soil.
Ingredients
Coffee is rich in nitrogen, phosphorus and potassium
Coffee grounds contain numerous nutrients, trace elements and tannic acids as well as traces of caffeine and bioactive substances such as antioxidants. This primarily applies to the residues in the coffee filter. More than ten percent of coffee grounds are formed by nitrogen-rich proteins. The average NPK ratio is 2-0, 4-0, 8. When prepared in the espresso pot, most of the ingredients pass into the coffee.
Effect of coffee grounds:
- Nitrogen: stimulates leaf growth
- Phosphorus: promotes flower formation and fruit ripening
- Potassium: supports cell structure and gives the plant stability
Coffee grounds are an organic fertilizer whose NPK ratio is beneficial for numerous plants. Due to the nitrogen-based nutrient composition, the grounds remaining in the coffee filter are ideal as additional fertilizer. It provides a good addition to compost, which is often low in nitrogen concentrations, and is a perfect alternative to commercial fertilizers.
Changes in pH
Coffee grounds usually have a pH value between 6.4 and 6.8 and are therefore in the slightly acidic to almost neutral range. This makes it unproblematic as a fertilizer for most plants. Researchers at Washington State University have found that pH varies greatly depending on the variety. According to their results, there are varieties with values between 4.6 and 5.26 and those whose values tend to be alkaline with values of 7.7 or 8.4.
Scientists were unable to confirm that the soil becomes acidic after long-term use of coffee grounds. The experiments showed that the pH value of the substrate treated with coffee grounds increased in the first two to three weeks and then gradually decreased. This suggests that the value fluctuates with microbial activity and does not remain constant over the long term.
Tip
Pay attention to the acidity of the coffee. From this it can be deduced in which environment the residues are located in the filter. Mix coffee grounds and eggshells, grinding them finely beforehand. The shells are calcareous.
This is how plants benefit from nutrients
According to gardening experts, coffee grounds as the top substrate layer have no or a greatly delayed effect on potted plants. This is because the powdered substance does not provide any plant-available nutrients. These are bound in the fine particles and must first be released by microorganisms in the soil.
It is therefore important that you work coffee grounds into the soil. You will achieve the best fertilizing results when used in the garden. Here, coffee grounds are used to build up the soil, as humus-forming substances are created during decomposition.
- Bacteria and fungi break down chemical components in coffee grounds
- Earthworms pull coffee particles into the soil, improving structure
- When the coffee powder is broken down, humic substances are formed
Background
Why fresh coffee grounds don't fertilize
The C/N ratio stands for the weight proportions of carbon (C) and nitrogen (N) that occur in soils. It is given as a number and serves as an important indicator of nitrogen availability for plants.
The smaller the number, the closer the carbon-nitrogen ratio and the more nitrogen is available to the plants. Fresh coffee grounds have a suboptimal ratio because the values are very high and fluctuate between 25 and 26. That is why fresh coffee grounds scattered on the ground do not bring any noticeable success.
The plants cannot absorb the available nitrogen in the soil. Over the course of a year, the coffee powder is broken down by microorganisms and the C/N ratio changes. It drops to 21, 13 and further to eleven or even nine, so that the plants only benefit from directly applied coffee grounds after a year. In this respect it behaves like fresh mowed material.
Application examples
Overfertilization in the garden is unlikely
If you use coffee grounds correctly, you can use them in a variety of ways in the garden. Over-fertilization is almost impossible. Rather, the plants suffer from suboptimal soil structures or an unfavorable water-air balance if you give too much coffee powder.
Coffee grounds have such different effects:
- Sugar beet seeds germinate better
- better growth of cabbage and soybean plants
- Seed growth of alfalfa, white and red clover is inhibited
- Geraniums, fern asparagus and three-master flowers show stunted growth
Lawn
Many grasses prefer a slightly acidic environment with a pH value of 5.5. Fertilizing with coffee grounds can improve the growth of your lawn. Sprinkle the dried powder evenly over the area and work it into the turf. Subsequent irrigation ensures that the particles are washed into soil pores.
This allows microorganisms to do their work and decompose the material. Alternatively, watering with a diluted coffee solution is recommended. Freshly brewed coffee is mixed with water in a ratio of 1:5 and then distributed with a watering can.
Tip
Check beforehand which species are in your lawn. Not all grasses tolerate coffee grounds. Italian ryegrass often grows in park lawns and shows growth problems when regularly fertilized with coffee grounds.
Citrus plants
The Mediterranean plants receive basic fertilization with long-term effects at the end of April in order to benefit throughout the entire growing season. Citrus plants mainly need nitrogen. Phosphate is important for flower and fruit development. However, all citrus species react sensitively to phosphorus-based fertilizers.
It is ideal if the concentrations of nitrogen and potassium are approximately the same and the phosphate content is lower. Coffee grounds are not suitable as a sole fertilizer, but should be added as a long-term fertilizer. It promotes lush growth and ensures lush green leaves.
Coordinated fertilization:
- fertilize only during the growth phase between April and September
- Trees in bright and warm locations have a higher nutrient requirement
- Fertilize potted plants only moderately in shady and cool locations
Compost
Coffee is also a blessing for compost
Over the course of several months, special bacteria and fungi that live in the compost break down all of the chemical components of the coffee grounds. Earthworms use the fine particles as a food source. Make sure the starting material is as diverse as possible to promote a variety of microorganisms.
Ideally, compost should contain no more than ten to 20 percent coffee grounds. Concentrations of more than 30 percent can have a negative impact on the macrohabitat. However, you don't have to worry about acidic compost developing. The pH value fluctuates constantly due to the activity of the microorganisms.
Mulching
Coffee grounds consist of fine particles and have a crumbly structure when dried. When it becomes saturated with moisture, it tends to compact easily. In this form, coffee grounds form a barrier against moisture and insulate the soil from air circulation. If you use coffee grounds for mulching, you should only apply the powder in thin layers and no more than an inch thick. Cover this layer with coarse organic materials such as wood chips.
Fresh coffee grounds are unsuitable:
- Floor can't breathe
- aerobic microorganisms do not get oxygen
- Mould formation is encouraged
Mushroom farming
Edible mushrooms can be grown in a flower pot filled with coffee grounds. The substrate should not be older than two to three days, as mold spores settle on the surface during long-term storage. Small amounts of coffee grounds are enough for the added mushroom mycelium to spread completely in the fresh substrate. This growth phase lasts about 14 to 28 days.
Vermehre Dein Pilzpaket mit eigenem Kaffeesatz - züchte selbst Edelpilze zuhause
Frequently asked questions
What are in the coffee grounds?
Coffee grounds contain numerous substances that do not get into the coffee when it is brewed. The residues contain various antioxidants such as caffeine, chlorogenic acids and the nitrogen-containing and yellowish-brown melanoidins.
The powder is rich in tannic acids and nitrogen-rich proteins. Non-water-soluble polysaccharides, which form the cell walls of the coffee bean, are also retained.
In addition to the nutrients nitrogen, phosphorus and potassium, which are important for plants, the coffee grounds contain essential oils that are responsible for the typical aroma. These have antioxidant and antimicrobial properties and have a deterrent effect on plant pests.
Can coffee grounds lower soil pH?
Linda Chalker-Scott from Washington State University has researched that adding coffee grounds to potting soil does not cause the pH value to drop to the acidic level. Rather, the value increases over the following period. Researchers suspect that this increase is caused by microbial activity. Only after the organisms have decomposed the material does the pH drop.
Can I compost coffee grounds without restrictions?
There is still no scientifically proven information about how much coffee grounds a compost heap can tolerate. The more varied the starting material is, the better your compost will work. In principle, ten to 20 percent coffee powder is not harmful to your compost. The coffee residues contain carbohydrates that are decomposed and broken down by the microorganisms.
How else can you use coffee grounds?
Encafé is a flower pot made from coffee grounds and natural wax. It serves as a plant pot that is placed in the ground with the plant. Here it decomposes and acts as a natural fertilizer. The aromatic substances protect the plant roots from infestation by pests such as nematodes.
