Think Twice Before Using Coffee Grounds To Fertilize Your Orchids

Orchids (family Orchidaceae) are gorgeous flowers that bloom with variously-colored petals including shades of white, pink, purple, blue, and yellow. However, they are one of the most difficult flowers to grow at home, and many aspiring gardeners have trouble keeping them alive. Orchids need a strict watering schedule, sufficient sunlight, and enough nutrients to survive many weeks. Though these flowers come with an instruction label that tells you how to care for them, keeping them alive can still be challenging. You might have researched tips and tricks that will help make it easier to care for your orchid. One typical search result is using leftover coffee grounds as fertilizer and adding them to your orchid's pot. These grounds are supposed to boost the plant's growth and provide plentiful nutrients to maintain its health. However, coffee grounds don't benefit some types of orchids, as this material can't be broken down properly in potting mixes.

There are two categories of orchids, namely terrestrial and epiphytes. Terrestrial orchids grow in soil, while epiphytes grow in the air or on trees and plants. Epiphytes are the most commonly grown orchid you can purchase at grocery stores or flower shops. When purchased, they're grown in a medium mix, which is a blend of materials like fir bark, peat moss, sphagnum moss, perlite, rock wool, and dried fern roots. These materials are lightweight and allow air to circulate throughout the pot. However, they also can't break down coffee grounds, making this fertilizer useless to epiphyte orchids.

Drawbacks to using coffee grounds as fertilizer

Coffee grounds can work well as a fertilizer for plants that grow in soil and that enjoy an acidic pH level. When the grounds are added around the plant, they are blended in with the rest of the soil. Over time, the coffee grounds are broken down and release nutrients like nitrogen that can benefit the plant. However, they don't work the same when added to epiphyte orchids, since these flowers grow in a medium mix. Therefore, when coffee grounds are added, they sit at the surface instead of blending with the materials like they would with soil. Further, they can also clog the orchid's mix, which can restrict airflow and prevent water from adequately draining, causing the roots to soak and eventually rot. Coffee grounds can also break down the mix, which may harm the flower's roots.

On the other hand, coffee is highly acidic, especially fresh coffee. Orchids enjoy a slightly-acidic to neutral pH in their medium to help them survive. If coffee grounds are added to a terrestrial orchid's pot, they could make the soil too acidic and harm the plant's roots. Plus, the coffee grounds by themselves cannot produce the nutrients that an orchid needs to survive. Instead, an earthworm needs to turn them into fertilizer, which isn't possible for indoor or epiphyte orchids. The combination of acidity and lack of nutrients can stunt the flower's growth and be detrimental to its health. 

When coffee beans and grounds may be beneficial

While you shouldn't use coffee grounds as your go-to fertilizer to help your orchids thrive, using a small amount of coffee beans occasionally doesn't hurt, as they have benefits other than providing nutrients. For example, coffee beans are phenomenal for repelling pests. Slugs and snails are enemies to orchids because they enjoy eating the leaves and stems of this plant. Other pests you might notice invading your orchids are mealybugs, aphids, and soft scales, which remove sap from these flowers, causing their leaves to turn yellow and stunting their growth. Placing a few coffee beans along the orchid's surface will repel pests with their intense smell. 

However, even though the beans will deter pests, they can attract other insects, so always keep an eye on your plant. The only insects you want around your orchid are earthworms because they can break down the coffee grounds into nutrients that could actually benefit the flower. If your terrestrial orchids grow outside, using coffee grounds as mulch can benefit them by attracting earthworms. The earthworms and bacteria in the soil will ensure the nutrients are broken down from the coffee grounds. However, you can't use coffee grounds as mulch for your indoor or outdoor epiphytic orchids because there won't be earthworms to help break down the grounds, and they also contain different types of bacteria than outdoor terrestrial types.