How to Use Coffee Grounds in Your Garden (and What Not to Do)
How do you use coffee grounds in garden beds? In this guide, we explore your options. Learn how to make the most out of your cup of joe, and where not to use those grounds on your plants.
Contents
You won’t get far on a gardening blog without finding an article about coffee grounds. This DIY additive is one of the most common gardening hacks out there, and also one of the most hotly debated.
My experience is that using coffee grounds in garden spaces is a fantastic way to boost plant growth. But it all depends on how you use it. As long as they’re brewed, this additive can be used as is, or composted with other garden materials.
There’s a wealth of misinformation online about coffee grounds. Let’s separate myth from fact to explain what to do (and what not to do) with coffee grounds in your garden.
Hungry Bin
The Hungry Bin creates an ideal living environment for compost worms. The worms quickly convert organic waste into castings and a nutrient-rich liquid, which are both high-quality natural fertilizers.
Myths about Coffee Grounds in the Garden
Before we jump into all the reasons we love coffee grounds, let’s dispel some myths. Here are the most common misconceptions about spent coffee grounds.
Myth 1: Coffee makes the soil pH more acidic
Sorry, but they aren’t a cure-all for your azaleas and blueberries, or even for the light acidity that tomato plants enjoy. While unused coffee grounds are a little acidic, used coffee grounds have a neutral pH. The acidity originally in the grounds is water-soluble, so it ends up in your coffee instead of the spent grounds.
Myth 2: The caffeine in coffee grounds will damage your plant
When you brew coffee, most of the caffeine goes into the cup. The used coffee grounds are left with about five milligrams of caffeine per gram. For comparison, an 8oz cup of coffee has 95 milligrams of caffeine. So, as long as you properly brew the coffee grounds beforehand and only apply a light dusting, the caffeine content will be too minimal to hurt the plants.
Myth 3: Fresh coffee grounds are a nitrogen fertilizer
They may be 2% nitrogen, but coffee grounds don’t supply significant amounts of nitrogen as a fertilizer to the soil. They also need time to decompose before this nitrogen is accessible. If you’re adding coffee grounds directly to nitrogen-loving plants, supplement the soil with a nitrogen slow-release fertilizer.
Benefits of Coffee Grounds for Plants
Like any fertilizer, coffee grounds provide nutrients and other trace minerals to the soil that can help boost plant growth. They contain phosphorus, calcium, magnesium, potassium, and more.
Along with providing nutrients, a coffee ground application may also remove toxic metals from the soil. Studies have been done on using fresh grounds to treat contaminated water and soil.
In order for soil to retain moisture without becoming waterlogged, it needs to be made of variable particle sizes. Gardeners often build up this soil structure with compost and other green materials. Coffee grounds will also get the job done, and just as well as most other organic matter! To really boost the soil texture, the used grounds should be mixed in instead of just laid on the soil surface.
Using coffee grounds may also discourage most cats from using your flower beds as a litter box. It should be noted that cats shouldn’t consume caffeine, even the small amounts in spent beans, so be wary of kitties in your yard with an unconventional appetite.
How to Use Coffee Grounds in Your Garden
Start by collecting spent coffee grounds. I like to keep a small bin by my coffee pot so I don’t forget to keep them. If you’re not much of a coffee drinker, you can ask a local coffee house for some used grounds. They go through plenty and are usually happy to share.
The type of roast you use doesn’t matter. Whether you drink blonde or espresso, those coffee beans all come from the same coffee plant. However, you don’t want to mix coffee grounds with used tea leaves or other food scraps. Those are best left to use in the compost bin.
What Not to Do
One of the reasons for all the confusion about whether coffee grounds are good for plants or not is because the danger is in the dose.
Too much of any additive in the soil will have negative effects on vegetable gardens, and coffee is particularly fickle. Large quantities of used coffee grounds build up too much of the same nutrients and overload the plants.
More dangerously, thick layers of coffee grounds can compact and become hydrophobic, shedding the water needed for plant growth. If this organic matter dries out, it’s very difficult to rehydrate.
The amount of coffee grounds varies depending on the current soil structure and water needs of the garden plants. Use it sparingly and never apply coffee grounds as a mulch to prevent compaction.
How to Apply
Add coffee grounds strategically to your vegetable garden. While you drink coffee in the morning, sprinkle coffee grounds directly on the soil and work them in. For larger amounts, layer compost, grass clippings, dried leaves, leaf mold, or other organic materials on top.
Even though coffee grounds are a good green material in compost, they shouldn’t be used on their own as mulch.
Like any amendment, you’ll need to reapply the grounds to the garden soil every few months. Always assess the soil first using a soil test so you understand what impact the grounds will have.
Composting
If you want to add your fresh coffee grounds to a compost pile, we have a complete guide here.
Coffee grounds are considered a green compost material and must be balanced with brown compost material. You also have the option to compost unbrewed coffee grounds for the green category, though you’ll need to be aware of the extra caffeine.
It’s beneficial for some acid-loving plants, but some ornamental and vegetable plants don’t appreciate the stimulant in their soil. Caffeine or not, worms love coffee grounds, so they’re a great addition to a garden worm bin.
Lastly, when you use coffee grounds as green compost material, you can throw in the paper coffee filters with it! A paper filter is typically a brown compost material, so it’ll complement the grounds perfectly in the compost pile.
Frequently Asked Questions
Which plants don’t like coffee grounds?
Coffee grounds can be beneficial for many plants when used correctly. As long as the coffee grounds are used, the acidity is not high enough to impact plants that prefer alkaline soil. Root crops may respond negatively when coffee grounds are used in large quantities due to the change in soil structure, but most plants will be fine if coffee grounds are used sparingly.
Can I use unbrewed coffee grounds in the garden?
You can use unbrewed coffee grounds in the garden, but it’s not recommended. Unbrewed coffee grounds are more acidic than used ones, which means they can significantly alter the soil. Acid-loving plants like azaleas and blueberries can benefit from added acidity, but as the results are unpredictable, it’s better to use other amendments to lower soil pH instead.
Are coffee grounds good for vegetable gardens?
Coffee grounds can be a valuable addition to vegetable gardens when used properly. They add organic matter to the soil, improving its structure and water retention capabilities. Composting coffee grounds before adding them to your vegetable garden is recommended, as it allows them to break down and release nutrients better.
Where should I not use coffee grounds in the garden?
Do not apply coffee grounds near seedlings or young plants, as large amounts of grounds can suppress growth. Additionally, don’t use coffee grounds in the garden as a thick mulch layer. They can form a crust that repels water and restricts air flow to the soil. Keep coffee grounds away from pet areas, as ingesting them can be harmful to animals.
