Should you put coffee grounds in your garden?

The simple idea of recycling spent coffee back to the earth stimulates green thumbs. But, is it smart to put coffee grounds in your garden? Should you join the java jolt and compost your brew?

Years ago Starbucks starting giving spent coffee grounds to local gardeners in Seattle on a first-come come, first-serve basis. The initiative was one way to fulfill the corporate mission of active environmental responsibility in communities in which they do business. The local stewardship spread quickly to all locations across North America.

Coffee grounds are typically wasted. To reduce waste, it’s tempting to add them directly to your the garden, worm bin, and compost pile. When gardeners, schools, parks, and nurseries use coffee grounds for compost and mulch, a valuable organic resource is returned to the earth.

The Language of Composting

In the language of composting, coffee grounds are ‘green’ nitrogen sources like grass clippings, vegetable scraps, and animal manures. The ‘brown’ components in compost are dead leaves, straw, sawdust, and hardwood ashes which contribute carbon.

Organic materials are composed of a carbon-nitrogen ratio. The carbon-nitrogen ratio in coffee grounds is 20:1 indicating the grounds are a good nitrogen source.

An analysis of the grounds reveals they contain the basic three nutrients of nitrogen, phosphorus, and potassium, aka N-P-K, for plant growth. The elements magnesium, copper, calcium, and sulfur are also in coffee grounds.

Why Use Coffee Grounds in Your Garden?

Gardeners extol the many benefits of the grounds:

• When mixed with brown materials in the compost bin, grounds generate heat to speed up decomposition.
• Coffee grounds absorb and retain moisture enabling them to affect the soil’s texture.
• The acidity of the grounds may be balanced with lime and /or hardwood ashes. However, many gardeners mulch acid loving plants like azaleas, camellias and blueberries with spent grounds. Acidic grounds keep your hydrangeas blue too.
• Tomato growers sidedress their plants for the nitrogen boost, added calcium and to suppress late blight.
• Grounds sprinkled on lawns contribute nitrogen, the greening nutrient for actively growing lawns.
• Hosta and lily growers find that coffee grounds repel slugs and snails.
• Earthworms enjoy a coffee klatch in a vermicompost bin and in no time their java castings perk-up the garden.

Outdoor container plants and indoor houseplants also respond favorably when you work grounds into the soil or use as a liquid plant fertilizer. Dilute the grounds in water to form an amber cordial. Similarly, rather than pouring leftover coffee down the drain, feed the elixir to your plants instead.

Precautions

Too much of anything is, well, too much. The old adage applies to coffee grounds in your garden.

A 2016 article in the Journal of Urban Forestry & Urban Greening study showed that coffee grounds may reduce plant growth when directly applied.

Applying coffee grounds directly to the soil may cause problems. Since wet coffee grounds can be mildly acidic, composting the grounds with kitchen scraps, yard debris and wood ashes forms the best product.

If wet grounds are worked into the soil or placed directly on the surface, they may form an unwanted mildew mat. To avoid this, allow the grounds to dry thoroughly before adding them to the soil.

In light of this, composting grounds may be the best course of action. The best way to assess what works in your garden? Experiment a little!

Take advantage of this free resource to brew a compost to energize your garden year-round.