I have heard that some gardeners use coffee
grounds as a plant fertilizer in
their gardens. Is it possible to use coffee grounds, or liquid
coffee, as a fertilizer for my houseplants?
It is best to
compost coffee grounds prior to using them around plants,
indoors or out. Fresh coffee grounds applied around plants can
cause them to suffer a temporary nitrogen deficiency, until
soil-dwelling microbes break the grounds down into a form where
their nutrients are available to your plants. There is also a chance
that a layer of coffee grounds around a plant can pack down and
impede water infiltration and aeration of the soil. By composting
them first, you avoid these problems.
More reasons to compost
your coffee grounds
Fresh coffee grounds support fungal growth and attract fruit
flies. While these side effects may not harm your plants, they
certainly create a nuisance you may wish to avoid indoors.
Materials for composting are divided into “greens” and “browns,”
depending on their carbon-to-nitrogen ratio. Materials high in
nitrogen are classified as greens while those high in carbon are
classified as browns.
Coffee grounds have a carbon-to-nitrogen
ration of 20:1, and should be considered green material in your
compost pile. The Environmental Protection Agency recommends that
coffee grounds not comprise more than 25 percent by volume of a
Other examples of “greens” include animal manure (not cat or dog),
fruit and vegetable peelings, and fresh grass clippings. “Browns”
include autumn leaves, straw, and wood chips. Composting proceeds
most efficiently when the carbon-to-nitrogen ratio of a compost pile
is 30:1, but compost happens even if the ratio of a pile is not
perfect. Simply add alternating layers of green and brown materials.
Start with a one-to-one ratio by volume and adjust as needed. If
your pile has a foul ammonia odor, it is probably too rich in
greens. Add more brown materials and mix in thoroughly to help
aerate the pile. If nothing seems to be happening, add greens to
heat the pile up.
Although I find that coffee grounds have an
I could not find an analysis for the beverage coffee. The analysis
is the percentage of NPK (nitrogen-phosphorus-potassium) in a container or
bag of fertilizer and is represented by the three numbers
prominently displayed on the label. They are always listed in that
order. I could not establish the beverage’s usefulness as a
However, it could be a useful amendment to maintain an
pH for houseplants that prefer that, including
African violets and
Norfolk Island pines, as long as you use it sparingly. While the
beverage is quite acidic, pH tests have revealed that coffee grounds
are only mildly acidic, ranging from 6.5 to 6.9. pH is measured on
an exponential scale of 0 – 14, with values below 7.0 acidic and
those above alkaline.
Coffee’s acidity is removed during the brewing
process, leaving the grounds with a near-neutral pH. The problem
with such home remedies is that it is hard to know how much is safe
to use or how often to use it to obtain the most benefit, especially
if you do not know the pH of the potting mix the plants are growing
in. The limited volume of soil in a pot does not have the same
buffering capacity as a much larger volume of soil in the landscape;
it is all too easy to overdo something that seems like it should be
good for our plants.
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