The internet is full of quick and easy gardening hacks that promise to make your plants as healthy and happy as possible.
Some are backed by science and sound gardening practices, while others are myths and legends passed down from generation to generation. Given the amount of conflicting information available, it can be difficult to separate fact from fiction.
Coffee grounds are often recommended as one of these hacks, claiming that they provide a variety of benefits for houseplants. Some advantages have a grain of truth, but they are not without disadvantages.
Take a look at these pros and cons of adding coffee grounds to houseplants to decide if it’s right for you.
We all know that plants need certain nutrients to grow and thrive. These are divided into:
- Macronutrients, needed in the highest amounts;
- Secondary nutrients, needed in slightly lower amounts;
- And micronutrients, which are needed in very small amounts.
If you’ve looked at a fertilizer package, you’ll see the abbreviation NPK, the three essential macronutrients. N stands for nitrogen, a nutrient that improves leaf and stem growth and gives green leaves their dark color.
According to Oregon State University, coffee grounds contain about 2% nitrogen by volume. They also contain phosphorus and potassium, but in small, almost negligible amounts.
Indoor plants are generally preferred for their foliage. This means that a high nitrogen content in the soil is essential to maintain its richness. Ground coffee, when used correctly, can be an excellent source of nitrogen to help your houseplants grow quickly and retain their beautiful leaves.
However, there is a caveat.
Coffee grounds alone are not sufficient as a nitrogen fertilizer. Studies have shown that the amount of soil needed to act as fertilizer can inhibit growth.
Their nitrogen is best used in compost, where it can break down with other materials to create a stronger, more balanced nutrient source for houseplants.
Coffee grounds retain moisture.
Peat is often recommended as a soil conditioner for houseplants. It retains moisture and improves soil structure, properties important for potted plants.
Unfortunately, peat is not a particularly durable material. There is some controversy surrounding its use because wetland ecosystems are damaged by the harvesting process.
This is where coffee grounds come in.
Coffee grounds are a great alternative to peat because they have similar properties. When coffee grounds are mixed with potting soil before planting, it retains moisture and improves soil structure.
They also stimulate the growth of microorganisms, which improves soil quality and nutrient availability.
Mix a few handfuls of coffee grounds into your houseplant mix when planting or transplanting to reap the benefits. Be sure to water the plants well afterward, as the site will become hydrophobic if it dries out completely.
One of the ways to make your indoor garden greener is to reuse coffee grounds in your soil or in your compost.
This way you use waste that would otherwise end up in the trash and limit the purchase of other products that serve the same purpose, but may not be as durable.
If you want to garden on a budget, look no further than the coffee corner in your kitchen.
If you’re already making regular coffee, coffee grounds are plentiful and completely free. In fact, you get more for your money by reusing land that would otherwise go to waste.
And if you’re not a coffee lover, there are ways to get free ground coffee. Many cafes have areas where they deposit their waste soil for avid gardeners to use absolutely free.
Because the quantities of coffee in stores are so much larger than what you use at home, there is always a constant supply. And when it comes to houseplants, you don’t need a lot of coffee grounds to make a big impact.
great in compost
With its high nitrogen content and ability to break down quickly, coffee grounds make a great addition to your compost.
Whether you have an indoor compost bucket in your kitchen or a large pile outside, throw in leftover soil to add nitrogen to the mix.
According to Oregon State University, coffee grounds have a carbon to nitrogen ratio of 20 to 1, very close to the 24 to 1 ratio needed to support microorganisms in compost. They also contribute to heat retention, which speeds up decomposition.
It attracts pests and diseases.
Coffee grounds are valued because they attract insects and beneficial microorganisms to the soil. Unfortunately, that means they also attract the wrong bugs.
Coffee grounds mixed into the soil or used as mulch can attract a wide variety of common houseplant pests.
They provide a wonderful home for fungus gnats that live in the soil. Humidity and humidity also attract other houseplant pests, such as thrips and scale insects.
The moisture-retaining properties of coffee grounds are also known to promote disease, especially fungal diseases that love the hot temperatures and high humidity that most houseplants prefer.
If you choose to mix coffee grounds into the soil, be on the lookout for signs of a pest or disease problem. Be sure to address any issues immediately with an insecticide spray, horticultural oil, or fungicide to prevent further spread.
Compact around the bottom
Coffee grounds retain a lot of moisture when wet. But when they dry, they compact and repel moisture. This is why dried coffee grounds from a coffee maker can become hard disks that are difficult to break down or rehydrate.
If you’ve added coffee grounds to your soil and it tends to flood your houseplants, it will be difficult to fully hydrate the soil. Because coffee grounds repel water, water will run down the sides of the pot rather than into the soil, leaving the roots completely dry.
This is a big problem when using soil as a mulch, as is often recommended. Once the coffee grounds have dried on the ground, the soil will repel all the water and prevent it from reaching the roots.
You also cannot keep the soil constantly moist, as this will lead to rotting of the roots.
If you use ground coffee, be diligent with the watering. Those who frequently flood their plants or water them multiple times should opt for another soil conditioner or mulch material.
May inhibit growth
Several studies on the use of coffee grounds have yielded unfortunate results. Unfortunately, contrary to what many expected, studies have shown that high levels of coffee grounds used as mulch or in soil can inhibit plant growth.
This phenomenon is due to the caffeine content of the coffee. While some claim that post-use caffeine is limited (about 20% of the initial amount), used coffee grounds still contain too much caffeine for houseplants.
Root growth is inhibited and germination is affected. Some leaves may also turn yellow and fall off the plant if the caffeine content is too high.
If you want to use coffee grounds around your houseplants, moderation is key. Don’t go overboard and amend your soil with half a ratio of coffee grounds, as this will likely do more harm than good.
Use it sparingly and never as a mulch to avoid damaging your houseplants.
This can lead to root rot.
While coffee grounds can cause problems for gardeners accustomed to underwater watering, they can also aggravate overwatering.
Overwatering is one of the most common causes of houseplant death. Excess moisture in the soil makes the roots soft and unable to absorb water and nutrients. This stunts growth and can eventually kill the plant if left untreated.
Because coffee grounds contain a lot of moisture, they can make overwatering problems worse if kept moist for long periods of time. Although water retention is often a benefit, it can be a burden for those who overdo it.
To reduce this risk, avoid watering on a schedule and test the soil’s moisture every few days. Most houseplants will need water again when the top few inches of soil have dried out.
Alternatively, you can use a moisture meter to make sure it will never be soaked or submerged in water again.
The jury is still out on the use of coffee grounds in indoor gardens. While there are clearly some benefits, there are also many risks.
If you’re determined to use your used coffee grounds, be sure to do so sparingly. Watch for signs of overuse to avoid permanent damage to your houseplants.