My favorite thing to do in the morning is to make a fresh cup of coffee. Nothing is better than that first sip to start my day. In fact, I can’t start my day without it or I am riddled with headaches, irritable, and basically non-functioning. As I was cleaning out the grounds to make a fresh pot, I remembered my mother saying she likes to sprinkle the grounds around her plants. Her anecdotal evidence found that she had fewer ants and gnats around the plants once she started adding spent coffee grounds to her potted plants. Now the old saying, “Mother knows best”, goes without saying when it comes to my mom but was there actually any truth here? Should we sprinkle coffee grounds in the garden?
Do plants also need a pick-me-up in the form of those deliciously roasted beans? I decided to do some digging around and was surprised by my findings.
There are several studies conducted on whether or not coffee grounds could benefit our plants and gardens and the short answer is yes; however, there are some negative findings as well.
Keep reading to learn about whether or not we should sprinkle coffee grounds in the garden to help improve plant quality or…not.
There are several reasons why coffee grounds should be added and used in plant soil; however, there are some caveats here as well. Coffee grounds are rich in nitrogen, phosphorus, and potassium and there is anecdotal evidence that coffee grounds are an effective way of pest control. However, there are several studies that show adding coffee grounds to a garden bed can lead to stunted plant growth and should be used with caution.
1. Sprinkle Coffee Grounds in the Garden as a Fertilizer?
There have been several studies on the effectiveness of using coffee grounds and whether or not amending the soil with spent coffee grounds can increase minerals such as nitrogen, phosphorus, and potassium.
One study states that when used properly, coffee can add these nutrients to the soil and become readily available for plants to use.
However, spent coffee grounds (SCG) should never be applied to areas that have been recently seeded.
Some studies have found that SCG reduced seed germination and in some instances were an effective weed control measure.
Here is where my deep dive into reading these studies took a turn.
I found another study suggesting that adding composted coffee grounds to garden beds can greatly reduce the ability of plants to grow.
In this study, broccoli, leek, radish, viola, and sunflowers were grown with and without spent coffee grounds. They found that all plants had decreased plant growth.
In fact, there was evidence of nitrate immobilization in the plants. Nitrate immobilization is the process in which minerals are taken up by organisms in the soil and therefore become unavailable to plants.
Here is the tricky part. For each study I found touting coffee as a great resource for gardeners I found another one refuting it.
So which one to believe?
Keep reading to find out what my research led me to.
Sprinkle Coffee Grounds in the Garden to Keep Pests Away?
Currently there is not scientific evidence that coffee grounds are a repellent to pests such as ants, slugs or snails.
However, that being said, there is a lot of anecdotal evidence suggesting otherwise.
Because coffee has a strong odor, it has been suggested that pests such as ants, snails, slugs and even rodents that could otherwise be detrimental to plants are averted.
Simply sprinkle coffee grounds in the garden around your plants to keep these pests away.
Do Coffee Grounds Effect Soil Acidity?
Most people assume the acidity of coffee will transfer to soil if spent coffee grounds are added. The research here is pretty clear.
Studies on whether or not coffee has impact on soil acidity say, no. It does not. The ranges of soil acidity amended with SCG found soil to be mildly acidic to somewhat alkaline.
I went a little bit further here and asked a group I belong to, “Should I sprinkle coffee grounds in the garden?”
The answers were a resounding, yes.
Application of SCG in the garden had positively effected roses, blueberries, blackberries and rhododendrons. All acidic loving plants.
Sprinkle Coffee Grounds in the Garden as a Form of Weed Control?
Here’s what the research said about using SCG as a form of weed control.
When researchers looked at different application methods for using SCG on weeds, they found not only did they improve soil quality but they were an effective method of controlling problematic weeds.
How was this possible? Don’t weeds also need fertile soil to grow?
They do. What they found was they were effective in controlling the germination rate of seeds.
Thus, SCG should not be used to treat establish weeds but as a pre-emergent treatment before weeds have the opportunity to establish themselves.
Some Tips if Using Coffee Grounds in Your Garden:
Based on my reading, I can share some tips that may be helpful if you decide to use spent coffee grounds in your garden.
1. Do not apply SCG in seeded beds. Wait for seeds to germinate or plant established seedlings before amending the soil.
2. Never use fresh grounds. Fresh grounds can lead to toxicity in the soil.
3. Don’t go overboard with the coffee. Apply a thin layer of grounds to the area you are amending.
4. Incorporating aged manure with the SCG is highly recommended. The two worked in unison to have the best overall impact on plant growth.
FAQ About Sprinkling Coffee Grounds in the Garden:
I don’t drink coffee…Where can I access spent coffee grounds?
Starbucks has a wonderful program that recycles their spent coffee grounds to gardeners. Simply call ahead or ask at your local spot.
Can I use coffee grounds directly in my garden soil?
Yes, coffee grounds can be used directly in the garden soil as a fertilizer or amendment.
How much coffee grounds should I use in my garden?
It is recommended to use coffee grounds in moderation, about 1/4 to 1/2 inch layer around the base of the plants.
Can I use coffee grounds as a mulch?
Yes, coffee grounds can be used as a mulch, but it is best to mix them with other organic materials like leaves, grass clippings, or wood chips.
Can I compost coffee grounds?
Yes, coffee grounds are great for composting as they add nitrogen to the compost and improve soil quality.
Final Thoughts
As a gardener, I am always looking for ways to help my plants reach their best potential.
Using spent coffee grounds seems like a great way to add nutrients to the soil, manage weeds as a pre-emergent treatment, and perhaps even deter pests. However, there should be some caution here as well.
I plan on incorporating this into my gardening routine on a small scale basis and observer the results. I’m looking forward to sharing my findings.
Please let me know in the comments below if you have any experiences with using SCG in your garden.
As always, happy growing!
