If you love hydrangeas, you are probably already aware that certain additions to the soil can change the color of the blooms produced by these beautiful plants (or at least, some kinds of them).
If you’re keen to get rich blue flowers, you might be wondering: do hydrangeas like coffee grounds?
The answer is that coffee grounds will enrich the soil and help to turn the blossoms into a deep, luxurious blue. They are a great thing to add in small quantities, and if you add them on a fairly regular basis, they will keep your hydrangeas healthy and beautiful.
Why Do Coffee Grounds Make Hydrangeas Blue?
Firstly, you might be wondering why putting coffee grounds on the soil alters the color of hydrangeas and makes their flowers turn blue. This isn’t something you can do with most plants, so why does it work with hydrangeas?
The answer is that hydrangeas respond to the pH value of the soil. Acidic soil produces blue flowers, while an alkaline soil will produce pink flowers.
Coffee grounds are highly acidic, so adding them to the soil around your hydrangeas will make the soil more acidic, lowering the pH value so that the plant produces blue flowers instead of pink ones. How does this work?
Decreasing the pH value helps to make certain minerals more available – in this case, aluminum. The plant can more easily absorb this from acidic soils, and this changes the color of its flowers because it has more of this mineral available.
It is important to note that although increased acidity can change the hue of the flowers, it won’t make the blooms more vibrant or brighter. If your hydrangea is pale, it will remain pale. All that adding coffee grounds will do is change the flowers from pink to purple or blue. It won’t darken them.
You should also bear in mind that some kinds of hydrangeas, namely the white ones, will not alter their flower color based on the pH of the soil. White hydrangeas will stay white regardless of the soil that they are in.
Flowers from the H. serrata and the H. macrophylla cultivars are the best for color changing.
Why Do Hydrangeas Like Coffee Grounds?
Hydrangeas enjoy coffee grounds for several reasons, and it isn’t just because the high acidity helps to make the aluminum more available to them. Coffee grounds are great for your garden and can be a good addition to many plants, although it is best not to add them to plants that prefer alkaline soil.
Just a few advantages of coffee include:
- Improved moisture retention, which hydrangeas love
- Improved drainage once the coffee grounds have turned into compost
- Improved nutrient balance in the soil because the coffee grounds contain nutrients and will release these as they break down
- Attractive to worms, which improve and aerate the soil around the hydrangea
Those are some compelling reasons to add coffee grounds around your hydrangeas and remember that if you later decide you would rather have pink blossoms, this is also achievable. You simply need to make the soil more alkaline and the flowers will revert to pink over a period of time.
What Should I Do First?
So, how do you actually apply the coffee grounds to the garden? Before you decide to do anything, you should purchase a soil testing kit to check your soil. If it is already very acidic, it is not advisable to add coffee grounds as these will further increase the acidity and could damage the plants.
If you’re trying to change the flowers to blue, the chances are that the soil is fairly alkaline, but you will still get valuable information from a soil test, so it’s useful to do. Any time you are planning to make a change to your garden, consider testing the soil first so you are operating from a position of knowledge.
Knowing how alkaline your soil is will at least let you know how much you’re going to need to alter it, and what quantity of coffee grounds you’re likely to need. If your soil is highly alkaline, it’s probably going to take a lot of time and effort to reduce the pH value enough to produce blue flowers.
How Should I Add Coffee Grounds?
If you have decided it’s worth doing, you can start adding coffee grounds straight away but think about your method first.
You can, if you like, just toss the used coffee grounds onto the garden around the base of your hydrangea. They will wash into the soil and slowly break down, adding to the acidity over time. This is quick, easy, and will mean you have started to alter the pH straight away.
However, this isn’t the prettiest approach to take, as the coffee grounds will mold and look messy while they are breaking down. Therefore, you might find that it’s better to dig the coffee grounds into the soil around your hydrangea, or add them to the surface of the soil and then mulch over the top of them.
Other people choose to add them to their compost piles and then use the compost on the hydrangea when it has broken down, but if you choose this method, bear in mind that compost loses its acidity fairly quickly and tends to be neutral or even slightly alkaline unless it is made with a significant bias toward acidity.
You may find that composting your coffee grounds first prevents them from having the desired effect on your hydrangea, but you can try this method if you like. Alternatively, look into making ericaceous compost at home and try this instead.
Do I Need To Keep Adding Coffee Grounds?
Yes, you will need to keep adding coffee grounds to your hydrangea to keep the soil acidic. If you don’t do this, it will slowly revert to neutral and eventually alkaline, and your hydrangea flowers will likewise grow pinker.
This will take time, but be aware that it also takes time to reverse the process and make them blue again, so it’s a good idea to add coffee grounds on a reasonably regular schedule if you decide that you want blue flowers.
Some people add them in quantity once a year, when they fertilize the hydrangea, while others just add coffee grounds sporadically, but keep doing so often enough to ensure the flowers stay blue.
What If I Grow My Hydrangea In A Pot?
Growing your hydrangea in a pot might seem a good way to keep the acidity close to the plant and reduce the need for constant top-ups of coffee grounds, and it will help to an extent. Often, people who want blue hydrangeas grow them in pots with ericaceous compost and add coffee grounds too.
This is a good method, but be aware that it won’t totally remove the need to add coffee grounds. You still need to keep making the soil acidic, but less of the soil will wash away from a potted plant, so you may find it easier to keep a potted hydrangea blue than one that has been planted in the ground.
How Fast Will The Flowers Turn Blue?
As with anything in the garden, you will need to be reasonably patient with your hydrangea; it will not turn blue overnight just because you’ve added a scoop of ground coffee. Usually, it will take a few months for the color of your plant’s flowers to change.
You may sometimes notice a change in hue within a few weeks, depending on the plant and how quickly it can take up the new nutrients, but it is often a slow process. Unfortunately (at least, if you prefer the blue), it is much easier to grow pink flowers and to change blue flowers to pink than it is to reverse this process.
The sooner you add coffee grounds, the sooner you will see blue flowers, so it’s a good idea to start adding them straight away if you can tolerate a little mess under your hydrangeas.
Does Adding Aluminum To The Soil Help?
Since hydrangeas need this to produce blue blossoms, you might be wondering whether the addition of aluminum would help the plants to change blue, but unfortunately, this is not necessarily the case. You need acidic soil for the plant to absorb the aluminum effectively.
However, if you do a soil test and it shows that aluminum levels are low, you should add some, as your plant can’t absorb what isn’t there! Adding an aluminum sulfate solution a few times a year can increase the acidity and ensure that your plant has aluminum to make use of.
Hydrangeas do like coffee grounds, yes. Coffee grounds are good for the garden as a whole (bar a few plants), but they help hydrangeas access aluminum in the soil, giving them a boost of this nutrient and turning them blue. They also help to keep the soil moist, which hydrangeas particularly enjoy.