Coffee grounds have a high nitrogen content, along with a few other nutrients plants can use. In compost, they help create organic matter that improves the ability of soil to hold water.
Excessive acidic soil can kill or hamper the growth of plants like asparagus fern, Chinese mustard, Italian ryegrass, lavender, orchids, rosemary, tomatoes, and geranium. The roots of these plants are also not potent to absorb the nutrients added by the coffee grounds in the soil.
These things are great for nutrient poor lawns and lawns on clay or sandy soil. However, coffee grounds still contain some residual caffeine, which can cause harm to the micro fauna in your soil, and that's why it is not recommended to apply coffee waste directly to your lawn.
Bottom line is that ground coffee will stay safe enough to drink pretty much indefinitely, barring any mold in the bag or a funky smell. But let's be honest, the coffee-drinking experience is more about the taste than anything else. If you don't like how it tastes, then you might as well dump it.
The good news: No, coffee doesn't really “go bad” in the way that bread grows mold or a banana slowly rots on your countertop. And drinking coffee made from old beans won't make you sick, even if the expiration date has passed. (We can't vouch for the taste, though.)
But did you know you can reuse this common kitchen waste item? Coffee grounds can contain nutrients and micronutrients like nitrogen, potassium, magnesium, calcium, and other trace minerals. Recycling your old coffee grounds is an easy way to fertilize plants and help reduce your household waste.
Since coffee grounds have such a pungent and intense smell, mosquitoes do not like to come near it. Mosquitoes are repulsed by all types of coffee, whether it is fresh, used, or burnt. The most effective way to use coffee grounds for mosquito control is by burning them, as it creates a stronger aroma.
The reality: coffee grounds can do more harm than good
Not a strong start. Then there's the fact that your soil might not even need more nitrogen, and an overload could restrict growth. So that's no good.
Coffee grounds have natural allelopathic properties, meaning that they inhibit the growth of some plants and weeds. They are able to prohibit germination and growth of some seeds. This is most effective on sprouting weed seeds and small seedlings.
The main ingredient in the used grounds is nitrogen, but there are traces of the other important nutrients like phosphorus and potassium. Fresh coffee is highly acidic, so may be useful for acid loving plants like magnolias and blueberries or for gardeners wanting to turn their hydrangeas blue.
Squirrels aren't the only wildlife that are likely to be repelled by coffee grounds. You can also count on coffee grounds to keep deer, chipmunks, and snails or slugs at bay.
By adding coffee grounds to your roses, you create a barrier that will keep pests away and allow your rose bushes to thrive. So if you're wondering whether coffee grounds are good for roses, the answer is a resounding yes! Coffee grounds are an inexpensive and readily available organic fertilizer for your roses.
Coffee grounds take three to four months or more to decompose, depending on the soil microbial activity and health. The more microbial activity of the soil, the more quickly coffee grounds decompose.
Diluting brewed coffee with an equal part water is plenty to do the job. Coffee grounds have been recommended in the past as an organic method to keep slugs and snails out of your flower and vegetable beds. Grounds will repel slugs, but the USDA research team confirms that a caffeine solution is more effective.
Coffee grounds can be used when planting perennials, shrubs and bushes, or added to the soil around those growing throughout the year. Adding a few tablespoons when planting perennials helps add nutrients and soil structure for long-term growth.
Yes, it's possible, but it should not be more than a thin sprinkling. If you add too much, the coffee grounds will form a dense layer on the surface of the potting soil that is impenetrable to water. On a regular basis, using leftover coffee to water your potted plants is a much better idea.
Coffee's bitter compounds are responsible for its repelling effects. These compounds make the coffee unpalatable to rats and mice. They will avoid areas where there is the use of coffee grounds.
How Often Should You Add Coffee Grounds to Plants? You can fertilize houseplants an average of 7 to 10 days in a row, but no more, as there is a risk of over-acidification of the soil. A cup of ground coffee should be added to the compost once a week.
Coffee beans, grounds and brewed coffee contain caffeine, a very dangerous and toxic chemical to cats and dogs. Ingestion can be life threatening. According to the Pet Poison Helpline, a moderate amount of coffee can easily cause death in small dogs or cats.
While many budding gardeners may be concerned that coffee grounds can attract pests, the reality is quite to the contrary. In fact, when implemented correctly, coffee grounds can be an effective way to repel certain pests such as wasps, snails, and mosquitoes.
Coffee grounds are highly acidic, they note, so they should be reserved for acid-loving plants like azaleas and blueberries. And if your soil is already high in nitrogen, the extra boost from coffee grounds could stunt the growth of fruits and flowers.
As for indoor plants, a teaspoon of spent coffee grounds mixed into the soil of most can work. Super-diluted coffee dregs can even be used for occasional watering. Remember that grounds help with water retention, so skip the succulents and plants that like the soil dry to avoid root rot.
Which plants shouldn't you try this with? Don't add eggshell fertilizer to plants that prefer acidic soil, like blueberries. Ericaceous plants such as mountain laurel, pieris and azaleas also fall into that category. In extreme cases, low acidity for plants could impact their overall health and/or the resulting crop.