Do gardenias like coffee grounds? Experts have their say

Do Gardenias like coffee grounds? Well, yes is the simple answer. But the gardening experts will tell you there's a little more to it than dumping your leftover grounds onto the soil and expecting that to work miracles.

Gardenias are beautiful but tricky plants to keep happy. Even though they are high maintenance, these powerfully fragrant blooms are well worth the effort. 

Whether grown as indoor plants or outside in the backyard, Gardenias require specific soil conditions to keep them thriving. 

Owing to its acidic properties, it is thought that coffee grounds can be a useful way to lower the pH of your soil, as well as adding essential nutrients. Our experts share how you can use them in the most beneficial way whilst not risking harm to your plant.

Truth or myth: do gardenias like coffee grounds?

'Classy they may be, gardenias are tricky to keep healthy and thriving, so please don’t blame yourself for any previous failings – I have killed several myself,' says horticulturalist and gardens writer Anne Swithinbank.

'Without the best care, plants tend to turn a sickly yellow and need supplementary feeding using a liquid fertilizer balanced for acid-loving plants,' she adds.

Here are some ideas on how to use coffee grounds as a plant fertilizer to boost the health of your gardenias. 

Anne Swithinbank

As a trained horticulturalist, garden writer and broadcaster, and the author of multiple books, Anne Swithinbank has an extensive knowledge about plants and gardening.

Add coffee grounds directly to the soil

As coffee grounds decompose, they release micronutrients and small amounts of nitrogen, phosphorus and potassium, so they are a mild, slow-release feed. 

This may not be strong enough for your gardenia if it is in need of additional fertilizing. So, supplementing with an ericaceous feed, like this Espoma Soil Acidifier from Garden Goods is advised.

Though some people believe in sprinkling coffee grounds straight on the soil, expert gardener Ruth Hayes has a different method: 'I don’t put them straight onto soil, but mix the grounds into compost instead.'

'Too much coffee applied directly can be toxic to plants, due to the amount of caffeine and polyphenols,' says Ruth. The right amount however can boost water retention as well as adding essential nutrients.

If you are making your own compost, adding coffee grounds will make the soil more acidic, meaning it's suited to acid-loving plants such as gardenias, as well as camellia and holly.

Ruth Hayes

Ruth Hayes is an experienced gardening editor and is horticulturally trained, with a qualification from the Royal Horticultural Society. Her work involves matching gardening tasks with each season, covering everything from sowing and planting, to pruning, taking cuttings, dealing with pests and diseases and keeping houseplants healthy. 

Make coffee grounds into fertilizer

'Many coffee shops are happy to give away their used coffee grounds,' says Tamsin Westhorpe, horticultural journalist and gardener.

'Coffee grounds can be turned into a liquid fertilizer by mixing 9oz of damp grounds in a five-gallon bucket of water and letting it sit outdoors to get to air temperature,' says Tamsin. 'It will need diluting before use, but can then be used as a liquid feed.' 

If you're storing coffee grounds for use on your gardenias, be sure to keep them in an air-tight container to retain their nutrients.

FAQs

Coffee grounds are good for boosting the acidity levels in your compost, which is optimum for gardenias to thrive. Making your own compost at home is an easy and free way to give your plants a much-needed nutrient boost.