Is Coffee Good for Plants? Using Grounds or Water

Is coffee good for plants? It's okay to water plants with leftover coffee or to add coffee grounds to the compost pile but learning when and why to use coffee in the garden will protect your plants. Only use black, unflavored coffee with this method to offer plants a source of nitrogen which can fertilize certain indoor and outdoor plants.

How Often to Water Plants With Coffee

Though it's tempting to pour what's left in your daily cup of coffee into your plants, it's best to stick to fertilizing with coffee once a week. If you decide to try watering houseplants or outdoor plants and vegetables with coffee, keep a close eye on your plants. If foliage starts yellowing or the tips of the leaves start turning brown, it's a sign that the coffee is adding too much acidity to the soil, or that you have to cut down on how often you water your plants with coffee or coffee grounds. Try feeding plants coffee once every two to four weeks and see how your plants tolerate the reduced schedule.

Coffee-Loving Plants and Vegetables

Plants that prefer more acidic soil may respond well to a weekly watering with coffee or sprinkling of coffee grounds. But take into consideration the plants that may prefer slightly acidic soil vs. plants that like very acidic soil. For example, roses and beans may prefer only very slightly acidic soil but blueberries prefer more acid. Here is a list of both indoor and outdoor plants that would love a sip of your leftover coffee:

Houseplants:

• African violets
• Phalaenopsis orchids
• Dieffenbachia
• Norfolk Island pines
• Nerve plants

Outdoor plants, trees, and shrubs:

• Azaleas
• Rhododendrons
• Siberian iris
• Lupine
• Impatiens
• Pine trees and shrubs
• Holly bushes
• Magnolia trees
  
• Roses
• Lilly-of-the-valley

Vegetables and fruits:

• Blueberries
• Potatoes
• Cucumbers
• Peppers
• Carrots
• Radishes
• Beans

Using Leftover Coffee Grounds

Coffee grounds can be a good source of nitrogen in your compost pile or when added directly to the soil in the garden. If added in fairly large amounts, they can raise the acidity level of the soil for acid-loving plants. Coffee grounds sprinkled over the ground around acid-loving plants serve as a mild acid fertilizer for them. Worms seem to love them, either in your garden or outdoor compost pile or in a vermicompost bin.

Coffee grounds are regarded as an effective natural deterrent to garden pests such as slugs, snails, and ants. Rumors of coffee grounds repelling deer may be overstated. Deer are voracious eaters, and a few cups of coffee grounds are unlikely to make much of a difference. Coffee grounds will discourage a mischievous cat from roaming in your garden, but their effectiveness on rabbits and other common garden rodents is unknown.

How to Use Leftover Liquid Coffee

When using leftover liquid coffee for plants, it is a good idea to first dilute your coffee with more water, especially if you prefer your daily cup of java on the strong side. But consider that in some workplaces, the only "watering" plants received is from emptying leftover coffee into the soil, and they often do quite well.