Rhododendrons: Do they like coffee grounds?

Rhododendrons are often used in landscaping, but many people don't realize that they can also be grown as a houseplant. Rhododendrons need lots of water and fertilizer to thrive, but what about fertilizing them with coffee grounds?

Rhododendron plants love coffee grounds. Coffee grounds provide an organic source of nitrogen for the plant while providing a natural pH balance. You can apply them to the soil or compost heap around your Rhododendron plants every three months. It is best to use fresh coffee grounds because Rhododendrons need acidic soil to grow well.

Benefits of coffee grounds for rhododendrons

Rhododendrons benefit from coffee grounds because they are acidic and help reduce the pH of the soil. Rhododendrons also need a lot of nitrogen to maintain their foliage, so coffee grounds have just enough nitrogen that will be beneficial for your rhododendron plants.

Coffee grounds also attack worms to your rhododendrons soil. Worms work to break down organic material in the soil. Rhododendrons need a good amount of organic material decomposed in the soil to produce new growth. Earthworms decompose organic matter and release microbes in the soil. Rhododendrons need microbes in their roots to help them grow and thrive.

Soil pH rhododendrons like

Rhododendrons grow best in a soil pH that is between neutral and acidic. Rhododendrons have a high tolerance to acidity, but grow best in soil that is between pH of 4.5 to 6.5. Rhododendrons are intolerant to alkaline soils with pH levels above eight.

Rhododendron leaves will show signs of yellowing if given too much nitrogen fertilizer, which has an alkalinity to it. Rhododendrons should be fertilized instead with phosphorus fertilizer such as bone meal for the best growth results.

Fresh coffee grounds support the soils pH of rhododendrons by adding a bit of acidity to the soil. Rhododendrons will not like used coffee grounds if they are planted in alkaline soils with pH levels over eight because this will cause yellowing leaves. Fresh coffee grounds or liquid coffee may be able to lower the pH to tolerable levels, but it could be hard to move the needle.

How to apply coffee grounds to rhododendrons

Coffee grounds can be applied to rhododendrons directly in the soil. Rhododendrons should be watered well before and after applying the coffee grounds. Rhododendron plants can also have soil amended with fresh or used, but not spoiled. Fresh coffee grounds should be used for a boost in acidity to their soil.

Used coffee grounds can be added to increase the pH of rhododendrons' soil as long as they are planted in an acidic soil that is less than a pH level of seven. You can neutralize the soil's high acid content by adding used coffee grounds.

Composting coffee grounds for rhododendrons

Coffee grounds can be composted and added to rhododendrons soil to help fertilize it. Rhododendrons are one of the many plants that can thrive in acidic soil, which is usually created with fresh composted coffee grounds or other organic materials like leaves and bark mulch. Fresh coffee grounds have a pH level between 4.5 and 6 on the scale of 14. Rhododendron flowers prefer to grow in soils where their roots will not be harmed by too much acidity. So you should try to stay about a pH of 5.

Coffee grounds can also serve as an activator for nitrogen-fixing bacteria found in your plant’s roots so they continue to provide nutrients for your garden plants throughout the year when weather conditions would otherwise make this difficult. As well, adding used coffee ground may create slightly more alkaline balance around your rhododendron plant, which can provide a buffer against the acidity of rain and other precipitation.

Problems if you give rhododendrons too much coffee grounds

Adding too much coffee grounds to rhododendrons can cause problems. Rhododendrons are susceptible to salt damage that occurs when the soil becomes too salty because of a high concentration of dissolved salts in the water used on your plants, or if fertilizer is applied at rates above what's required for healthy plant growth and development. Too much nitrogen can steal water away from the soil and cause salts to deposit in your soil.

If you soil already contains a lot of nitrogen, adding an excessive amount of coffee grounds could push the soil to dangerous levels of nitrogen for your plants. The result can be leaf yellowing (chlorosis), brown spots on leaves, and healthy plant growth and development. Chlorosis appears as yellowish-brown spots on leaves that could eventually lead to decreased leaf leaf drop.

Small amounts of coffee grounds will not cause a great increase in nitrogen levels. You should test your soil before adding coffee grounds to the soil to determine how much nitrogen is present.

You also need to consider that adding too much coffee grounds to your rhododendrons soil can cause problems with water draining in the soil. Rhododendrons are susceptible to waterlogging because they have a shallow root system. Rhododendron roots need oxygen and nutrients in the soil, but too much coffee grounds will prevent air from entering the ground to help with this process.

Therefore, you should avoid adding excessive amounts of coffee grounds so your rhododendrons don't become saturated with water.


You can use coffee grounds to help fertilize your rhododendrons, but there are a few important things you should know before adding them. The pH of the soil and nitrogen levels need to be considered so that it doesn't disrupt the natural balance in your garden. For those who don't have space for a compost pile, they can just add them directly into the potting mix without worry about whether or not they will break down over time.

The next time you have a cup of coffee, consider saving your grounds and adding them to the soil around your plants or composting them before use if they're not too old.