Blue hydrangeas are the envy of gardeners everywhere. Even though there are blue flowers on other plants, the big, round blue flowers of a hydrangea are the best. For those who want to change the color of their hydrangeas or just get brighter blue flowers, there are a lot of people who try out different ideas and theories. That’s what makes gardening fun!
One idea is that coffee grounds can make your garden grow the most beautiful blue hydrangeas you’ve ever seen. We all know that things we find on the internet don’t always work. Sometimes they lead to great tricks, and other times they do.
So, what about coffee grounds? Do they really turn your hydrangea blue or make their color stand out more? Or will adding them to the soil of your plant be yet another failed garden hack? The answer isn’t clear-cut, but let’s look into it more and help you decide if it’s something you should try this season!
The short answer is “maybe. ” Unfortunately it’s not cut and dry. Most evidence is anecdotal, with some online publications recommending it. But changing the color of these popular shrubs really comes down to science.
Hydrangea have pH sensitive flowers. If the soil is more acidic and has a 5. 5 or below pH, that will favor blue blooms. The lower pH levels allow the plant to absorb more aluminum, producing blue flowers. It’s possible that coffee grounds could lower the pH levels of the soil where you live. If this happens, the grounds could be used to help grow beautiful blue flowers.
As mentioned, this “gardening hack” can have roots based on science and testing. There’s a few conditions that would need to be met to get it right. It starts with the type of hydrangea you have. Some types will not change color, no matter what you do to the soil.
Others are pH sensitive, so it’s important to determine your hydrangea type and variety/cultivar first. Once that’s done, it’s on to soil composition, and altering the pH levels of your soil. So, let’s take a deeper look at what you can expect for each of these important factors.
Hydrangeas are prized for their lush, colorful blooms that brighten gardens each summer. But getting those flowers to turn an intense blue hue can be tricky. The secret lies in amending soil with used coffee grounds. However, timing is critical for the best results.
Why Coffee Grounds Turn Hydrangeas Blue
The pigments in hydrangea flowers are affected by the pH of the soil. More acidic soil below pH 5.5 triggers the plant to uptake aluminum and produce anthocyanin which shifts colors toward blue and purple shades.
Coffee grounds provide organic acids that acidify and lower the pH of soil. This makes the aluminum already present more available to the plant. The more acidic the soil becomes, the bluer the hydrangea blooms.
Best Time to Add Coffee Grounds
It takes time for coffee grounds to affect soil pH enough to influence hydrangea color. A single application right before blooming won’t instantly make flowers blue
Instead, begin amending soil the fall before you want blue blooms. Add used grounds regularly over the next several months leading up to summer.
Start in Late Fall
The ideal time to start is late fall, such as November, in most regions This gives the organic matter plenty of time to break down over winter and allow the acidity to permeate the root zone before growth resumes in spring
Spreading grounds over frozen soil in winter won’t be as effective. Wait until just before expected first frost to get started.
Repeat Through Spring
Continue adding fresh coffee grounds every 2-4 weeks from fall through early spring. Target the area below the plant’s leaf canopy, which contains the bulk of the roots.
Dig grounds into the top few inches of soil or simply scatter on the surface around the base. Rain and irrigation will leach the acidity down into the root zone over time.
Avoid Summer Additions
Stop adding grounds by early summer before blooming begins. Adding too much acidity during summer growth can potentially burn roots and leaves.
Let the acidification from the previous fall and spring applications work its way into the plant to influence flower color. Resume adding grounds next fall for the following year.
How Much Coffee to Use
There is no exact formula for how many pounds of used coffee grounds are needed per hydrangea. Soil composition and pH vary. Plan to apply grounds regularly over an extended period.
As a general guide, scatter 2-3 handfuls per mature plant every 2-4 weeks through fall and spring. Apply around the drip line, not piled around the stem.
Monitor soil pH every few months to gauge acidity levels. Lowering pH by just 0.5-1 point can make a difference in flower color.
Other Tips for Blue Blooms
While coffee grounds provide the missing acidity, other factors also influence hydrangea color:
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Choose varieties capable of blue flowers – Look for mophead and lacecap types
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Grow in morning sun and afternoon shade – Less sun prevents flowers from fading
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Use aluminum sulfate if needed – Lowers pH more for very alkaline soils
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Prune properly – Remove only dead stems, not healthy ones
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Avoid excessive nitrogen fertilizer – Can inhibit flowering and cause pink tinges
With the right hydrangea varieties and proper care focused on soil acidification, you can enjoy gorgeous blue blooms summer after summer. The secret lies in consistently incorporating used coffee grounds into the soil over time.
Frequently Asked Questions About Coffee Grounds for Hydrangeas
Turning hydrangea flowers blue with coffee grounds requires some patience and trial and error. If you’re new to using this garden trick, here are answers to some commonly asked questions.
How long does it take for coffee grounds to turn hydrangeas blue?
It can take 1-2 years of regular coffee applications to acidify soil and change flower color. Be patient and keep amending soil each fall through spring. Established plants may show some blue shades within the first year.
Will used coffee filters also help turn hydrangeas blue?
Yes, the grounds left in wet coffee filters contribute acidity just like fresh grounds. Place used filters around plants and lightly work them into the top inch or two of soil to break down.
Is brewed leftover coffee effective for hydrangeas?
Yes, the acids remain in brewed coffee. Pour leftover morning coffee or rinse saved grounds with water to make “coffee tea.” Avoid using sweetened or flavored coffee.
How often should I add coffee grounds to hydrangeas?
Scatter fresh grounds around plants every 2-4 weeks from late fall to early spring. Or simply work them into soil once a month during this period for more gradual acidification.
Should I add other amendments along with coffee grounds?
Coffee alone provides the acidity. But you can also mix in compost or well-aged manure to improve soil structure and nutrients at the same time.
With the right variety, proper care, sufficient sun, and repeated feedings of used coffee grounds, you can unlock the gorgeous blue hues hidden within your hydrangea blooms.
So, What About Coffee Grounds?
There have been reports of gardeners getting wonderful results using coffee grounds in their soil. As you likely know, especially if you are an avid coffee drinker like myself, coffee is acidic. After giving it some thought, it seems likely that this could also make your soil acidic.
Organic materials, like coffee grounds, are always better for our plants and soil because they last longer. When you work with organic materials, you don’t have to worry as much about applying too much and burning the roots of your plants.
What Makes Them Blue?
As a species, hydrangeas like acidic soil, and the pH of your soil can affect each flower. What does this really mean? It means that the lower the pH of your soil, the more acidic it will be, and the bluer the flowers will be.
The more alkaline your soil, the more pink or red their blooms will be. If the soil is neutral, the flowers will be purple, and sometimes they will be a mix of blue and pink.
The lower pH of your soil the more acidic it is. Acidic soil allows for the uptake of any aluminum that may be in the soil. Aluminum is what will give your hydrangeas that beautiful blue hue.
Soil pH is measured from 0-14. A rating of 7 is a neutral soil. Any ratings below 7 are an acidic soil, while ratings above a 7 are sweet or alkaline. The best soil pH for blue flowers is right around 5. 5.