Can You Use Coffee Grounds As Fertilizer For Indoor Cacti Plants?

Anyone who's jumped down the rabbit hole of gardening hacks that give you an instant green thumb has surely discovered the beauty of coffee grounds. After enjoying their caffeine kick, plant parents add these morning leftovers to their houseplants. The reason? "Used coffee grounds have a small amount of vital nutrients like nitrogen and some micronutrients," explains House Digest's Garden Editor and In-House Master Gardener Tiffany Selvey in an exclusive interview. Though she qualifies them as more of a nutrient boost than a significant source of fertilizer. Plus, "They are often used to improve the soil structure, helping with drainage while retaining some moisture," she adds. 

Given their benefits, you may have wondered whether you should fertilize your indoor cacti with leftover coffee grounds. Turns out, it may not be the best idea. While many indoor houseplants thrive when given coffee grounds, indoor cacti are an outlier. Explaining why this is the case, Selvey states, "I would be cautious about adding coffee grounds to the soil of an indoor cactus because of its ability to hold on to moisture. Most cacti need to dry out completely between waterings." Considering many homeowners end up killing their houseplants by overwatering, it makes sense to avoid any moisture-retentive natural additives. However, you may make an exception when repotting a cactus, advises Selvey.

Although indoor cacti enjoy being pot-bound and rather benefit from it as the soil dries out faster, you must size up their containers every couple of years or more once their roots start peeking out of the drainage holes. That way, you can also refresh the soil and restore the lost nutrients. Sadly, repotting can stress the plant. For this reason, our in-house master gardener thinks adding used coffee grounds to the cacti soil during repotting may be beneficial, as they can help stave off some transplant shock.

In her exclusive interview with House Digest, Tiffany Selvey elaborates, "...some coffee grounds added to the soil when repotting can help with drainage and provide some nutrients to help decrease transplant shock." Since the nutrients are released slowly into the soil, they're unlikely to burn the roots. Instead, they'll help the plant to recover quickly. Moreover, homeowners are warned against watering their cacti houseplants for two weeks after repotting to avoid damaging any wounded roots.

There is an art to making coffee, and using the leftover grounds afterward for your houseplants — you can't simply sprinkle them all over the potting soil. "Coffee grounds should never be added to the surface of the soil, so don't plan to use them unless you are repotting your cacti," explains Tiffany Selvey during her exclusive interview with House Digest. "Adding them to the surface of the soil is a recipe for pests and mold." Many flies find coffee grounds attractive and wreak havoc by nibbling on the plant roots. So, make sure to mix them into the potting soil for the desired results, or not at all if you're feeling risk-averse.

But how do you determine the exact amount of coffee to add? By feeling the planter's size! "If you do want to use coffee grounds in your indoor cacti soil, the amount really depends on how big your planter is and how much planting medium you have," clarifies Selvey. Her rule of thumb? "It's not an exact science, but I recommend erring on the side of caution and add a handful to large planters and just a few tablespoons to smaller ones." Ultimately, you must use the discarded grounds in moderation, lest the soil hold too much water around the roots. "Just make sure the mixture drains well to prevent root rot," is Selvey's final advice, and your cacti should be golden green.