Coffee grounds are a free and very plentiful source of organic matter that can be used to enrich and amend garden soils.
(Editor's Note: This article was originally published on September 26, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
I rarely pass a Starbucks store without going inside. My ardent devotion is not due to a FrappuccinoTM dependency (though I have begun to savor a refreshing iced vanilla latte as an afternoon energy booster). My frequent visits to Starbucks are not motivated by a craving for caffeine, but instead by a desire to gladly haul away the coffee purveyor's garbage. I am adamantly addicted to gathering used coffee grounds as a soil amendment for my garden beds. Starbucks is more than willing to be a codependent enabling partner in support of my habit. Since about 1995, Starbucks stores have made thousands of pounds of used coffee grounds available at no charge to gardeners.
If I were somewhat more of a romantic poet, I would surely write odes and recite amorous sonnets with mandolin accompaniment to praise the many virtures of used coffee grounds. Coffee grounds are just about the most perfect organic additive that any gardener might find to "perk" up a listless garden!
Coffee Grounds will:
Increase moisture retention in sandy soils so that less irrigation water is required, and make it possible for plants to more easily survive short periods of drought.
Provide a more loose and friable texture to heavy clay soils.
Encourage a healthy population of beneficial microbes that will break down the coffee grounds and other organic matter, thereby converting nutrients that are locked up in organic matter into chemicals that plant roots can absorb.
Help earthworms to be hyped up and happy as they hustle to digest the coffee grounds and leave behind their fecund worm castings to enrich the soil.
Act as a "slow release" source of nitrogen to promote lush, green plant growth.1
Provide immediate increases in essential nutrients of phosphorus and potassium, as well as the beneficial minor nutrients of magnesium, calcium, and copper.1
Provide release over time of other essential plant growth minerals, possibly making the use of chemical fertilizers unnecessary.1
Provide a gentle, gradual, perhaps nearly negligible, localized increase in soil acidity (enough to eventually turn your hydrangea flowers blue, if coffee grounds are applied on a regular basis).
Serve as a substitute or enhancement for manure in compost piles.2
Create higher temperatures in compost piles to help kill weed seeds and pathogens (the highest temperatures of around 150° F can be reached when compost materials include about 25% coffee grounds, which is the recommended maximum amount of coffee grounds for a compost pile).2
Add a pleasant aroma to your garden (if you like the smell of coffee) for a short time after the coffee grounds are applied.
Provide some control of slugs and snails.3 Possibly deter other insects and garden pests (but most of these claims lack scientific verification).
Increase the green hue of your lawn through nitrogen feeding when coffee grounds are spread evenly across the lawn surface (1 cu. yd. of coffee grounds for 1,000 sq. ft., raked in to provide a depth of about 1/8 inch of coffee grounds).4
And for an additional, more global benefit: Recycling coffee grounds for use as a soil amendment will reduce the amount of organic matter that is unnecessarily going to landfills, thereby helping to reduce emissions of methane, a greenhouse gas. Organic materials produce significant amounts of methane as a byproduct of their decomposition in landfills.
The few problems that coffee grounds might cause include:
Drying out and caking on the soil surface,
Providing a moist surface that promotes mold and fungi, and
Preventing water from permeating down to reach plant roots.
Coffee grounds applied directly to the soil should be less than about one-quarter inch thick
These problems would generally occur only if the coffee grounds are applied very thickly or when coffee grounds are not worked into the soil surface. If you have a lot of coffee grounds and only a few plants, or are using coffee grounds for plants in containers, it would be best to blend your coffee grounds with some garden soil or potting soil prior to applying the grounds to your plants. You may also compost the coffee grounds and then use a portion of the finished compost about once per month. Applying full-strength coffee grounds in a heap directly to the soil surface in a confined space could result in some or all of the problems listed above. Coffee grounds contain trace amounts of chlorine and sodium salts which have the potential to be harmful to plants. However, these salts would cause a problem only when too hefty a portion of coffee grounds is amassed upon a small garden plot or potted plant.
Though it may seem reasonable to assume that coffee grounds are acidic due to the many acids found in coffee beans,4 laboratory tests have demonstrated that most of the acid is removed from coffee along with the caffeine during the brewing process. Used coffee grounds actually have a pH close to neutral (about 6.2 pH) and only a very minor trace of caffeine remains in coffee grounds. Starbucks and other companies have done laboratory analyses of coffee grounds to determine what nutrients the coffee grounds might provide for plants. The results of the tests show approximately the same values as those reported for a test conducted by Sunset magazine:
10 lbs N/yd3 (nitrogen per cubic yard) .01 lb immediately available (0.9%)
Nearly all potassium and magnesium immediately available 50% of copper and calcium immediately available All other elements are bound in organic matter, available by slow release
pH = 6.2 (slightly acid, pH = 7 is neutral)
Salinity (ECe: Electrical Conductivity of solute extract) 3.7 dS/m (deciSiemens/meter) Water soluble salts of potassium, magnesium, sodium, chloride (sodium and chloride are inconsequentially low)
1mm (0.03937 inches)
442 lbs organic matter/cubic yard
Carbon to Nitrogen ratio = 24:1
While the lab tests confirm that coffee grounds are nearly neutral in pH, the reports from gardeners indicate that there is a gradual acidifying effect from coffee grounds. To be completely on the safe side, you may want to limit heavy use of coffee grounds to only those plants that prefer an acidified soil. These include common landscape plants such as azaleas, rhododendrons, gardenias, camellias, hollies, dogwood trees, and most conifers.
Prior to using coffee grounds as a soil amendment, a soil pH test should be conducted to ensure that you won't be making an already acid soil even more acid. Most local Extension Offices will provide a soil pH test at no charge. A pH test is a basic requirement prior to using any soil for gardening. The test is definitely needed prior to amending the soil with lime or sulfur or other soil amendments that may alter the soil pH.
How to apply coffee grounds to your soil:
Most sources recommend that coffee grounds should be treated with a composting process prior to applying the coffee grounds to garden plantings. The composting process frees up the nitrogen in the coffee grounds and converts it into a form that plant roots can readily absorb.
However, many gardeners do apply uncomposted coffee grounds around the base of plants without incurring any problems. When using uncomposted coffee grounds, it may be best to use a hand rake to gently work the coffee grounds into the top few inches of the soil without disturbing the plant roots.
If you are preparing a new garden plot for planting, you can add about 35% by volume of used coffee grounds, and then till or otherwise work the grounds into the top six to eight inches of the soil.1
Since it is my dogged desire to disregard any reasonable advice in favor of my own heretical experimentation, I prefer to toss coffee grounds straight from the pot into my garden. My yard is surrounded at the perimeter by eight-foot high, decades-old azaleas and Japanese yew (Podocarpus macrophyllus) hedges. These hedges were the legacy of previous gardeners and were already well-established when I bought the property. It is in these border areas that I use most of the coffee grounds that I obtain. My method of spreading coffee grounds follows my usual path of least effort. I simply throw the coffee grounds by the handful onto the top of the azaleas and yew and let the coffee grounds rain down through the leaves. This creates a randomly dispersed sprinkling of the coffee grounds across the soil surface beneath the plants and avoids the problems that might occur from heavy accumulations of the grounds. Some of the coffee grounds will stick to the fuzzy leaves of my azalea plants. I've not noticed any leaf damage resulting from this temporary condition. If you find that this brown residue of coffee grounds on the leaves is unattractive, you may want to scatter your coffee grounds just prior to a rainstorm or use overhead irrigation after applying the grounds to hose off the leaves. I also slather the base of my azaleas with as many bags of oak leaves as my neighbors' yard crews can rake. I generally nab these bags of leaves as soon as they hit the curb and dump the bags in piles under my azaleas. The resulting layer of about six inches of brown leaf mulch approximates the ratio of 1 part coffee grounds to 3 parts brown leaves that is recommended for composting coffee grounds. In effect, I create a slow-cooker composting process beneath my azaleas and podocarpus. This process provides a sustainable and consistent gradual release of nutrients without the need for other fertilizers. By maintaining a thick mulch of brown leaves under my azaleas, I feel comfortable tossing on as many pounds of coffee grounds as I can hunt down and carry home.
Where to obtain coffee grounds? If you happen to have one or more of the ubiquitous Starbucks outlets in your vicinity of the Universe, you will have access to an abundant supply of coffee grounds. Starbucks reuses the foil bags in which they receive their gourmet roasted coffee beans to serve as packaging for the coffee grounds from their espresso machines and other coffee brewing equipment. The neatly wrapped bags are sealed with a colorful sticker proclaiming "Grounds for Your Garden." The coffee grounds are then placed discreetly in a small brown metal schoolroom-type trash can, generally situated near the front entrance of the store.
Since word has spread far and wide about the Starbucks coffee grounds recycling initiative, and since many other gardeners share my considerable unconditional affection for coffee grounds, you will quite often find the coffee grounds receptacle empty. Gardeners lacking nerve and gumption might turn away in defeat at the sight of the empty coffee grounds bin. I, however, brazenly approach the barristas, wait for a moment when they are not tied up with taking an order or preparing a caffeine infusion, then ask politely if there are any coffee grounds they want to toss out. I immediately add to my request before they can answer that I am willing to take the coffee grounds in the trash bag where the grounds are collected behind the counter without the need for the staff to funnel the grounds into the fancy foil wrappers. This usually results in delight from the Starbucks employees because it saves them from performing what I imagine is one of their least favorite tasks of bagging up messy coffee grounds. I am well steeped in the capacity to ignore disdaining stares from the unenlightened. After gathering up the coffee grounds, I march resolutely out of the store through the throng of lap-toppers, my head held high, smug in my contentment that I am a politically-correct Earth-saver, proudly carrying the dark, rich bounty of coffee grounds in a bulging garbage bag.
You will receive a superb quality of used coffee grounds from Starbucks. Most of the grounds will be in the form of small compressed "pucks" from the espresso machines. The grounds will have the texture and consistency of moist talcum powder and will be boldly aromatic. There are no paper filters used in the brewing process, or if filters are used, they are disposed separately from the coffee grounds. The Starbucks bags of pure coffee grounds weigh approximately five pounds each. I am unashamed in my greed and will make several trips to my car in order to haul away all the bagged coffee grounds that are available. As soon as I arrive home with the coffee grounds, if time allows, I buoyantly bounce around my garden borders, hurling the coffee grounds onto the tops of my acid-loving plants. I frequently, however, forget that I have a horde of coffee grounds in the trunk of our car until Christina (who uses the vehicle more frequently) points out to me that the auto is becoming ripe with the redolence of rotting coffee. I don't worry if the long-forgotten grounds have developed a thin patina of blue mold. I toss the grounds onto the plants as usual, hoping that a hit of penicillin may give the plants an additional immune boost.
In addition to Starbucks, there are countless other coffee houses and sources where you can obtain copious amounts of coffee grounds. In fact, the results of a survey conducted by MasterComposter.com revealed that only 13% of gardeners using coffee grounds get their grounds from coffee shops. The other 87% get their coffee grounds from their own kitchens and the kitchens of their relatives, neighbors, and friends; from the office coffee service; from schools and houses of worship; from restaurants and fast food establishments; and from all the other places where large quantities of coffee are prepared. Approximately seven-million metric tons (fifteen-billion pounds) of coffee beans are generated worldwide each year.5 We may logically assume that about the same amount of tonnage is thrown away as used coffee grounds. Regardless of where you live, there should be plenty of coffee grounds available to you if you are willing to ask around and make arrangements to pick up the grounds.
If your supplier of coffee grounds mixes the coffee filter papers in with the coffee grounds, I have learned from personal experience that it is best to remove the paper filters prior to storing the coffee grounds for even a few days. It doesn't take long for mold to develop on the paper and for the paper to begin to decompose. A plastic bag filled with coffee grounds and paper filters will become a rancid and sometimes maggot-infested mess within a matter of days. It is very unpleasant to pick out the paper filters from the coffee grounds at that stage of decomposition. If you are gathering coffee grounds for your compost pile, you can toss the paper filters into the pile, or layer them along with the coffee grounds when doing "lasagna" composting. I have tried to use the paper filters on the soil surface around my plants prior to applying coffee grounds in the hope that the paper will act as a weed barrier before it disintegrates. My experiences show, however, that the paper filters are much more likely to dry out to a completely sere, wispy, butterfly wing-thinness and will blow away prior to any break down of the paper fibers.
If it seems like too much work to gather and spread coffee grounds, you can still provide a benefit to your plants by using cold, diluted leftover brewed coffee to occasionally water your plants. The coffee nutrients will awaken new growth without alarming your plants with a sudden jolt. You can also prepare a fertilizer "tea" by placing about one pound of coffee grounds in a mesh bag in a container of about five gallons of water.7 You can water your plants from time-to-time with this weak coffee solution.
It is my hope that you will not be able to drink another cup of coffee without wondering what happened to the coffee grounds that were used to make your beverage. I would certainly encourage you to track down those coffee grounds and use them in your garden. When you are enjoying that next cuppa joe, give some thought to your Joe Pye Weed and remember that it might also appreciate a bit of stimulation from some used coffee grounds.
**Please check below for an important late-breaking update in regard to the effectiveness of coffee grounds in preventing and helping to eliminate Asian Scale on Sago Palms. Feel free to provide comments in the feedback area (bottom of the page, below) with your own experiences and any additional information in regard to using coffee grounds in your garden.
Read testimonials about the benefits that coffee grounds and diluted coffee provide to plants at this webpage at sustainableenterprises.com
Roasted coffee beans photo credit from Wikipedia Commons - "This image has been released into the public domain by its author, MarkSweep. This applies worldwide. In some countries this may not be legally possible; if so: MarkSweep grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law." Full size photo and further copyright information can be found at this webpage.
Photo of compost tube bin photo credit from Wikipedia Commons - Photo by Ellen Levy Finch Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License." Additional copyright information and the full-size photo are found at this link.
Thanks to DG Admin Melody for creating the images used as illustrations for this and other "National Coffee Day - September 29," coffee-themed articles!
Starbucks™ and Frappuccino™ are registered trademarks of Starbucks coffee company. The author has no affiliation with Starbucks, other than to frequently abscond with their used coffee grounds.
Photo of Starbucks used coffee grounds foil packaging by the author. All copyrights reserved.
Today is day four of the Dave's Garden focus on coffee. Be sure and read the other articles leading up to National Coffee Day, September 29.
Jeremy (JaxFlaGardener) is a frequent contributor to the Florida Forum and other forums on Dave's Garden. In an ideal world, he would spend nearly every waking moment gardening, oil painting, and writing. Lacking such a Utopia, he currently works part-time in the Horticulture Department at the Jacksonville (Florida) Zoo and Gardens. His own half-acre garden is a hodgepodge of just about everything that will grow in Zone 8b/9a, with a homemade greenhouse for his orchids. He is a Master Gardener who esteems digging in the dirt more than book learning, but greatly enjoys research about plants and botanical nomenclature. He is pictured here with one of his large paintings, "The Healer's Leaves," based on a wonderful photo by DGer GardenWife of Ricinus communis (Castor Oil Plant) used by permission.