Many creative ways to use used coffee grounds as fertilizer for plants are being shared online. However, DIY gardening remedies and anecdotal recommendations are not always based in fact. When it comes to benefiting houseplants, we dug into the science to understand the pros and cons of using coffee grounds as fertilizer. Read on for expert tips for using coffee grounds on your plants, and how (if at all) you should use them.
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Is coffee grounds suitable for houseplants?
Studies have shown both positive and negative effects of using coffee grounds on plants. Although coffee grounds contain nutrients that are beneficial to plant growth, they also contain chemicals that can inhibit the growth of certain plants. The effect of coffee grounds on plants also depends on its use. “It's best to apply coffee grounds indirectly (by adding them directly to the plant's soil) to houseplants to prevent mold from forming,” says gardener Leaura Alderson.
Horticulturist Linda Chalker-Scott says, “When used properly, coffee grounds provide nutrients and other benefits that promote plant growth. In general, they can be used as a soil amendment for plants. It's only composted coffee grounds.'' The ground also provides organic matter to the soil, which helps improve soil structure and facilitates the movement of air and water through the soil profile.
Ornamental plants that like coffee grounds
Through personal research, Alderson discovered that the following plants respond positively to coffee grounds: “This list is based on plants that like and/or can tolerate acidity below a neutral pH of 7.0,” Alderson explains. This includes:
African violets (Saintpaulia spp.) Aloe vera (Aloe barbadensis) Rhododendrons (Rhododendron spp.) Bromeliads (Bromeliaceae) Christmas cactus (Schistola spp.) Golden pothos (Epipremnum aureum) Jade (Crassula ovata) Peace lily (Spathiphyllum spp.) Persian cyclamen (Cyclamen persicum) )Philodendron (Philodendron bipinnatifidum)Rose, miniature (Rosa chinensis minima)Snake plant (Sansevieria trifasciata)Spider plant (Chlorophytum comosum)
Many lists of coffee grounds-loving plants assume that coffee grounds are acidic, but this is not the case with used coffee grounds, especially when composted. Some gardeners use fertilizer tea made directly from used coffee grounds rather than composted coffee grounds. Because tea is made by steeping uncomposted grounds in water, we know that acids are extracted, so “it's natural for the coffee to have some sourness,” Alderson says. For best results, use composted meal rather than fertilizer tea.
Benefits of using coffee grounds for plants
First, it is important to point out that we are discussing the use of used coffee grounds that have already been used to make coffee. This is important because fresh and used coffee grounds and freshly brewed coffee all have different properties. For example, freshly brewed coffee is very acidic, but used coffee grounds are not. Let's take a look at the nutrients found in used coffee grounds and how they benefit your plants.
contains nutrients
The powder left over after brewing coffee contains a mixture of proteins, oils, and carbohydrates that were not extracted by water. Nitrogen-rich proteins make up about 10% of used coffee grounds, and plants use large amounts of nitrogen. Coffee grounds also contain potassium, trace amounts of phosphorous, and other micronutrients that are used by plants, such as calcium, iron, magnesium, and zinc.
Contributing to healthy soil
Although coffee grounds contain beneficial nutrients, plants cannot use them directly from coffee grounds. Coffee grounds must first be broken down by composting or natural decomposition. Through these processes, soil microorganisms convert elemental nutrients contained in coffee grounds and other organic materials into compounds that can be used by plants.
suppress disease
Several studies have demonstrated that coffee grounds used as part of a compost mix suppressed some pathogens in experiments conducted with vegetable crops. Affected diseases include common fungal rots and wilts such as Fusarium, Pythium, and Sclerotinia. However, disease control by coffee grounds has not been studied in garden plants or ornamental plants.
help the earth
By reusing used coffee grounds for plants, we help reduce food waste. You can reuse the coffee grounds from brewing coffee at home or collect used coffee grounds from your local coffee shop. This is a great way to collect large amounts of coffee grounds to use in your garden.
Disadvantages of using coffee grounds for plants
In addition to the potential benefits of using coffee grounds on plants, research has also revealed negative effects associated with this practice. Although most of these challenges have only been observed in crops or landscape plants, they may also apply to ornamental plants.
suppress plant growth
Just as caffeine has both positive and negative effects on humans, the same is true for plants. A study investigating the effects of used coffee grounds applied directly to some plants in a field trial found that while weed growth was reduced, to everyone's delight, plant growth was also reduced. . Unfortunately, very few houseplants have been directly tested.
toxic to some plants
One of the many suggested uses for used coffee grounds is to fertilize the soil of houseplants. As Chalker-Scott explains, fresh ground is clearly phytotoxic (poisonous) to a variety of plants, so it is not recommended to use them as amendments or mulches.
Create a moisture barrier
Another reason to avoid direct application of coffee grounds is that finely cut coffee grounds tend to compact and form a moisture barrier across the soil surface. This can promote fungal growth and reduce air flow to the plant roots.
harm good bacteria
Adding coffee grounds to your plant's soil may help ward off harmful bacteria, but it can also harm beneficial bacteria. Without beneficial bacteria, plants can be exposed to diseases and pests.
How to use coffee grounds for plants
Research suggests that adding used grounds to a compost tumbler or compost bin and using the finished compost is the best way to use coffee as a plant fertilizer. Chalker-Scott reports that compost containing 10 to 20 percent coffee grounds is most effective.
Gardeners have long used composted coffee grounds to improve garden soil, and this has many benefits, but how do you use this compost for potted plants? A popular recommendation is to make a fertilizer tea from composted coffee grounds and use this as food for houseplants.?
But Chalker Scott said: “There's no science to support using compost tea for anything. Compost is great. (But) the water that leaches out of it is a very weak fertilizer, and that's about it.”
Add coffee grounds to potted plants
When it comes to houseplants, just like in the garden, the greatest benefits come from using finished compost directly as a soil amendment or mulch. An easy way to use finished compost is to add a thin layer on top of the potting soil in your container.
Adding finished compost to your potting mix is another great way to reap the benefits of composted coffee grounds. Finished compost can be integrated with potting mix to stimulate soil health and plant growth. Compost loosens the soil, minimizes compaction, improves drainage and aeration, and increases the soil's ability to hold nutrients. Potting mixes can be amended by adding up to 30% finished compost.
Adding coffee-infused compost to your houseplants once or twice a year is a good way to add extra compost while repotting your plants. This method does not have the same problems as applying coffee grounds directly to top-dressed soil because the composted material is lighter, does not compact in the same way, and allows air and water to move quickly.
FAQ
Which plants hate coffee grounds?
Some plants do not benefit from adding coffee grounds to the soil. Plants such as lilac and lavender prefer alkaline soil, so slight acidity can harm them. Caffeine in coffee grounds can also harm some herbs and geraniums. Before adding coffee grounds, be sure to research the optimal conditions for your plants. And keep in mind that the best way to add coffee grounds is indirectly through composting.
Can coffee filters be composted?
Depending on the material of the coffee filter, it may be possible to compost it along with coffee grounds. You can compost coffee filters made from paper or other compostable materials. Do not compost items made from synthetic materials (such as nylon or plastic).
Does coffee grounds lower soil pH?
Let's separate fact from fiction and look at recommendations for using coffee grounds to lower soil pH. Coffee is very acidic, but the coffee grounds left after brewing are not considered acidic. This is because the acids in coffee are water-soluble and remain in the mug rather than the coffee grounds.
“The pH of decomposed coffee grounds is not stable and should not be assumed to always or ever be acidic… (therefore) do not assume that coffee grounds will produce acidic compost,” says Choker.・Mr. Scott writes. .
Studies investigating the effect of used coffee grounds on soil pH have shown lower pH levels. However, the pH of composted coffee grounds varies considerably from study to study. Although this study was not conducted in potting soil, similar results can be expected.