Coffee and plants make a dynamic duo due to the high acid content of the java and a plant's natural need for nitrogen. There are many plants that benefit from a regular dose of coffee, including perennial roses, annuals like begonias and garden plants such as tomatoes. Houseplants such as jade, pothos and African violets can also use coffee as fertilizer. You can administer brewed coffee regularly, in place of water, or use the grounds as a soil supplement.
Watering with Coffee
Find out how your plants like to take their coffee: brewed or ground. Popular plants, such as jade, pothos, African violets, spider plants, flowering cactuses such as Christmas cactuses and other flowering plants such as roses, hydrangeas, tomatoes and blueberries all like fresh brewed coffee as opposed to left over coffee grounds. However, squash, lettuce, azaleas and gardenias prefer their coffee in the form of grounds which are added to the soil.
Brew coffee as normal. You may brew coffee as strong as you normally would, however, according to Marion Owen, co-author of "Chicken Soup for the Gardener's Soul," if you drink strong coffee it may be a good idea to dilute it prior to using it on your plants. In addition, do not use flavored coffees or coffee which has cream or sugar in it.
Allow the coffee to cool down before attempting to use it on plants. Warm or hot coffee may damage the plant's roots.
Give your plant as much coffee as you would give water. Supplement the coffee with added water if necessary. As with most plants, it is only necessary to water if the soil at 1 inch depth is dried out.
During the growing season feed your plants with coffee regularly as a fertilizer. However, in the off-season only use coffee every now and again to supplement the soil.