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Fertilizing houseplants is an important aspect of houseplant care, and there are plenty of natural fertilizers that you may have thought of trying. One that many people ask is if you can use coffee grounds to fertilize indoor plants.
Can you use coffee grounds to fertilize indoor plants?- Coffee grounds can be used to fertilize indoor plants, but it’s best to compost them first. Directly applying coffee grounds to potting soil indoors can cause excessive moisture retention, fungal overgrowth, and even stunt plant growth.
Coffee grounds are a very useful nutrient source that indoor plants can use effectively, and a very cost effective fertilizer. Read on for how to use them effectively, without harming your houseplants.
Why use coffee grounds to fertilize indoor plants?
Coffee grounds are a very common kitchen waste, full of nutrients that most people just throw away. They are readily available, free and they are high in nitrogen, one of the most important nutrients for healthy plant growth. Using coffee grounds on indoor plants is also a good way to reduce household waste production.
People have been using coffee grounds in their gardens for years with reasonable success, so it’s only natural for people to experiment with using coffee grounds to fertilize indoor plants. As we’ll see, this is definitely something you should consider, but there are significant problems with their use.
What are the best ways to use coffee grounds to fertilize indoor plants
Although some people may be inclined to add coffee grounds directly to the top of the soil on their indoor plants, this is not recommended and can cause a number of problems. However, there are three good options for how your indoor plants can benefit from coffee grounds as a fertilizer.
1. Use coffee grounds to make compost
By far the best way to use coffee grounds is to use them to make compost. Add all your used coffee grounds to your compost pile and wait until your compost is ready to use.
Most indoor plants come from tropical climates, where they get most of their nutrition from decaying organic matter that has been produced by the dense vegetation around and above them.
Homemade compost largely recreates this natural process and will supply plenty of nutrients for your houseplants to thrive. The high nitrogen content of the coffee grounds (NPK 2.1-0.3-0.3) will be balanced out by the other components of the compost you have made.
You can either apply this compost when you replant or you can add a thin layer on top of the soil or work it into the top few inches of soil.
Some people will not use homemade compost on their houseplants because of concerns about the odor produced by the compost. In my experience this is not a problem. Any odor produced dissipates very quickly and can be largely prevented by working the compost into the soil.
There are two things to keep in mind when using homemade compost on your houseplants.
First, applying excessive compost can lead to leaf burn and symptoms of nutrient toxicity. Add no more than an inch of compost to the pot to prevent this.
Second, because compost is rich in organic matter, it will naturally retain water, which can increase the risk of overwatering. Take this into account and go easy on watering to prevent problems.
2. Make liquid coffee potting compost
While I wouldn’t recommend pouring coffee over the soil on your houseplants, you can make a “compost tea” with your coffee grounds that works well on your houseplants.
There are many different methods of making compost tea, but one of the easiest is to simply put your coffee grounds in a container full of water and let it steep for 1-2 weeks, stirring every few days.
As the coffee begins to break down, it will release nutrients into the water, while also being a rich breeding ground for beneficial bacteria. You can then strain this liquid through cheesecloth and use it to water your plants.
This not only provides a good source of nutrients, but adds beneficial bacteria, which can improve the health of the soil and your plants.
3. Add coffee grounds to the potting mix when repotting
Because coffee grounds are an organic material, they release their nutrient content slowly as they decompose into the soil. This allows you to use coffee grounds as a slow release fertilizer when mixed with the regular potting mix you use for your plants.
Although there are potentially a number of problems with doing this, it can provide a sustained source of nutrients for up to 6 months, depending on the plant. Coffee grounds are one of many natural houseplant fertilizers, but you should make sure to use them correctly to get the best results.
Coffee grounds contain a large amount of nitrogen compared to phosphorus and potassium. Indoor plants with relatively higher phosphorus and potassium requirements may not do as well as they should if you only use coffee grounds to fertilize your plants.
Using coffee grounds in your potting mix comes with some issues that I will talk about in the next section.
Problems with using coffee grounds to fertilize indoor plants
While we’ve discussed some of the ways you might want to use coffee grounds to fertilize your indoor plants, it’s important to highlight the negative aspects in a little more detail.
Excessive moisture retention
Coffee grounds are exceptionally good at retaining moisture. Their organic nature and fine particles act like a sponge and retain moisture in the soil. This is a big negative, as the most common problem for most indoor plant caretakers is overwatering.
Adding coffee grounds to the soil greatly increases the risk of overwatering your houseplants, which can spell disaster for your plants.
If you use coffee grounds on your indoor plants, either directly or as part of a compost, you can reduce the risk of overwatering by changing the composition of the soil you use.
By adding more coarse sand or perlite to the potting mix, this will increase drainage, allowing the soil to dry out faster after watering, reducing the risk of overwatering and root rot.
Other options include using a porous pot and/or a smaller pot. Both of these changes will lead to faster drying of the soil, reducing the risk of overwatering.
Promotes fungal growth
This is more of a problem if you add coffee grounds to the surface of the soil on your houseplants. Coffee grounds are an ideal breeding ground for fungal organisms, and this can lead to fungal diseases in your plants.
It’s especially frustrating when you try to help feed your plants and promote their health, only to give them a fungal disease that can do a lot of damage.
This problem can be reduced by ensuring that the coffee grounds are worked well into the soil. If you use coffee grounds compost or add coffee grounds when repotting, this risk is ideally reduced.
Attracts pests
Although some pests may be deterred by coffee grounds, there are many pests and insects that will be attracted to the conditions that coffee grounds in the soil of your potted plants create.
Again, this highlights why it is not recommended to add coffee grounds to the surface of the soil. Using coffee grounds to make compost is the absolute best option if you want to use coffee grounds to fertilize indoor plants.
Coffee grounds can actually stunt the growth of some plants
There have been a number of small-scale studies that have shown that coffee grounds added directly to the soil can actually inhibit plant growth, especially in seedlings and young plants. This is believed to be due to the caffeine content of the coffee grounds.
There doesn’t seem to be any evidence that using coffee grounds to make compost causes the same problem, so again this seems to be the best option for using coffee grounds to fertilize your indoor plants.
There are much better options
I guess the bottom line is that using coffee grounds to fertilize houseplants is less than ideal. There are many better natural or synthetic options for fertilizing your plants, and you’re probably better off using coffee grounds for your outdoor plants, or using this kitchen waste in some other way.
Many people can now have their kitchen and garden waste collected by their municipality separately from the rest of their waste. This enables local authorities to recycle this organic waste as compost, to be used in more suitable environments.
Conclusion
Although you can use coffee grounds to fertilize indoor plants, you need to avoid the problems that come with this. For most people, I would recommend using coffee grounds for your outdoor garden and using alternative options to fertilize your houseplants.
If you really want to continue using coffee grounds, making compost or a compost tea with them is much more likely to lead to a positive result.
Read this article if you want to learn more natural ways to fertilize your houseplants. Alternatively, see this article to find out what fertilizer I use on almost all of my indoor plants.
