Using Coffee Grounds as Garden Fertilizer

01/09/2019 | Ken Davis Fertilizer, In the Garden, Spring

by Ken Lain, the mountain gardener

If you make a daily pot of coffee, you have a fabulous source of the organic matter right at your fingertips. Coffee grounds can make your garden happier in several ways, and not just that coffee gives you more energy for weeding and pruning! So, don’t toss those grounds. Put them to work.

Coffee in Compost
There are two types of compost material: brown and green. Your coffee grounds may be brown in color, but in compost jargon they are green, meaning an item that is rich in nitrogen. Coffee grounds are approximately 1.45% percent nitrogen. They also contain magnesium, calcium, potassium, and other trace minerals beneficial to plants.

Adding coffee grounds and used paper coffee filters to your compost provides green compost material, as do grass clippings and kitchen scraps. “Greens” must be balanced with brown compost materials, such as dry leaves and newspapers. For an effective compost the ratio should be a 4 parts brown to 1 part green compost material. If you have too much green stuff, your compost starts to smell. If you don’t have enough, your compost won’t heat up enough.

Fertilize With Coffee Grounds
Add coffee grounds directly to garden soil. You can rake it into the top couple inches of soil, or just sprinkle the grounds on top of the soil, without raking. In smaller amounts, especially when mixed with dry materials, coffee grounds provide gardens with nitrogen. Used coffee grounds are actually nearly neutral in pH, so they shouldn’t cause concerns about their acidity.

To make coffee ground “tea” add 2 cups of used coffee grounds to a 5 gallons of water. Let the “tea” steep for a few hours or overnight. Use this concoction as a liquid fertilizer for garden and container plants. It also makes an excellent foliar feed when sprayed directly on plant leaves and stems.

Feed Earthworms
Worms love coffee grounds, so once a week add coffee grounds to your worm bin. Just don’t add too many at once, because the acidity can bother earthworms. A cup or so of grounds per week for a small worm bin is ideal. Keep in mind that earthworms are attracted to garden soil that is mixed with coffee grounds used as fertilizer.

Keep Away Pests
Create a slug and snail barrier. Coffee grounds are abrasive, so a barrier of grounds placed near slug-prone plants may just save them from these garden pests. However, be warned that some researchers quibble with this advice and don’t think it useful. You may want to have a backup plan in mind if it doesn’t work. However, many cats dislike the smell of coffee grounds and avoid using a garden as a litter box if coffee grounds are mixed in with the soil.

Fresh Coffee Grounds for Acid-Loving Plants
While used coffee grounds are only slightly acidic, fresh (unbrewed) coffee grounds are much more acidic. Acid-loving plants like hydrangeas, rhododendrons, azaleas, lily-of-the-valley, blueberries, carrots, and radishes get a boost from fresh grounds. Caution:  Tomatoes do NOT like fresh coffee grounds, so keep them away from the part of the garden with tomato plants!!.  Fertilizing with unbrewed grounds can be a good use for coffee in your pantry that is getting old or is a blend you bought for visiting friends but isn’t your usual Cup-of-Joe.

Fresh coffee grounds contain most of their acid and caffeine content.  So be cautious when using fresh grounds around pets or your Wire Terrier may become extremely WIRED!!.

Dissenting Research Into Coffee Grounds in the Garden
One research study found that using spent coffee grounds in growing broccoli, leeks, radishes, violas, and sunflowers resulted in weaker growth in all soil types, with or without additional fertilizers. The good news is that the coffee grounds improved the water retention capacity of the soil and decreased weed growth. Researchers thought that the poorer growth was due to the plant-toxic compounds naturally present in coffee grounds. If you aren’t getting the results you hoped for by fertilizing with coffee grounds, you may want to experiment with and without them in your gardens.

 For many years Starbucks shops have been offering used coffee grounds to gardeners.  No charge.

The recipe to blend Perfect Mountain Garden Soil – for amendments that add vitality and richness to garden soils go to Preparing Garden Soils for Spring Planting.

Until the next issue, I’ll be helping gardeners here at Watters Garden Center.

Ken Lain can be found throughout the week at Watters Garden Center, 1815 W. Iron Springs Rd in Prescott, or contacted through his web site at or .