How to change the color of hydrangeas? The first thing to know is why hydrangeas change colors? It depends on the type of hydrangea, the pH of the soil, and the aluminum content in the soil.
Although the color change is usually mainly attributed to the soil pH, it is actually the aluminum that caused the color change. If there is aluminum in the soil, the flowers will be blue. In the absence of aluminum, the flowers will turn pink. However, soil pH plays a key role in color changes: aluminum can move more freely in low pH (acidic) soil.
Which hydrangeas can change color
Not all hydrangea flowers can change colors. The lacecap and mophead hydrangeas (H. macrophyllas) and H. serrata varieties of hydrangea can change the color of their flowers by changing the soil chemical properties.
- When grown in acidic soils containing aluminum, the color of the flowers will turn blue.
- When growing in alkaline soil, the color of the flowers will turn pink.
Which hydrangeas cannot change color
White or cream-colored hydrangeas are not affected by the pH of the soil, and white flowers will remain white forever. such as Annabelle hydrangeas, oakleaf hydrangeas and members of the PeeGee family.
When to try to change the color of hydrangea
Our suggestion is to wait for 2 years after planting the hydrangea to try to change its color. In general, it is not a good idea to damage the pH of the soil too much. Even if your hydrangea tree roots are healthy, trying to change the color will also affect the health of the hydrangea.
How long does the color change take
The process of changing the color of the hydrangea will be slow, and may require a color correction cycle of several weeks or even months. So don’t expect to see the results immediately. Generally, the effect of turning a blue hydrangea into pink is much easier than the effect of turning a pink hydrangea into blue.
How to change the color of hydrangea
After understanding all of the above, increasing the acidity (turning blue) or alkalinity (turning pink) will make the job easier. The first thing you need to do is test the pH of the soil.
Soil sample testing
Use tools to collect the soil around 15-20 deep around the root of the hydrangea. Try to collect samples in multiple areas around the hydrangea to obtain the average acidity of the sample. We have 2 methods to detect the pH of the sample.
Local USDA cooperative laboratory for testing
Seal the sample, contact the local USDA research center or the local nursery and garden center, and then send the sample for analysis to obtain a pH report. This may charge a small fee for soil testing.
Test the pH of the soil by yourself using a commercial soil test kit
Go to a garden shop to buy a commercial soil test kit, dig a hole in the middle of the soil sample, and fill it with distilled water. Then follow the instruction manual, insert the attached test probe or test strip into the turbid water, and wait for the time specified in the instructions. At the end of this time, please read the number on the probe or compare the color of the test strip with the chart on the product packaging to determine the pH of the soil.
If the number you see is less than 7, it means your soil is acidic. If it is higher than 7, it is alkaline. A reading of exactly 7 indicates that your soil has a neutral pH.
Make hydrangea blue
If your hydrangea is pink (because your soil is alkaline), and you want the hydrangea to turn blue, you need to make the soil acidic by increasing the aluminum content.
Purchase aluminum sulfate or collect natural acidic organic matter
We can add aluminum sulfate to the soil. It can safely increase the acidity level of alkaline soil. Aluminum sulfate is available in most garden supply stores. A 4 pound aluminum sulfate usually only costs you $ 12-15.
If you don’t want to spend money, you can also do this by adding natural acidic organic materials (such as conifer needles, sawdust, sphagnum moss, and oak leaves) to the soil, or coffee grounds, fruit and vegetable peels, grass clippings. Make the soil acidic.
Use aluminum sulfate solvent or natural organic matter
Follow the instructions on the product label and mix 1/4 ounce of aluminum sulfate with 1 gallon of water until the mixture is completely dissolved. Throughout the growing season, soak the soil with the mixed solution and continue every 2-4 weeks. Then test the pH of the soil. If your soil pH is greater than 7, you will need to soak the solution again. Similarly, it may take several weeks or even months before you notice that the color is gradually turning blue.
If you intend to use natural organic materials to lower the pH of the soil, simply treat it below the surface of the soil and then water the plants as usual.
Apply 25-5-30 fertilizer
The choice of fertilizer will also affect the color change. Every spring, follow the instructions to apply high potassium and low phosphorus 25-5-30 fertilizer. While the plant maintains nutrition, low phosphorus will help produce a good blue color.
Remember, changing the pH of the soil is a gradual process and does not produce dark blue flowers overnight. The color change may take up to one year.
Make the hydrangea pink
To change the hydrangea from blue to pink, you need to remove aluminum from the soil. The only way is to add garden lime to the soil to help increase the pH.
Buy garden lime
The most common way to become alkaline is to add powdered garden lime. Also called dolomite ash. You can find it at any garden center and online retailer.
Lime evenly in the soil
In spring or autumn, spread the garden lime evenly on the soil at the bottom of the plant and water it. To avoid overloading the soil, the gardening professional recommends a ratio of 4 pounds per 100 square feet (per pound may cost $ 2-8).
Throughout the spring and summer growing season, lime is applied repeatedly every 3-4 weeks. You may see the color of the hydrangea gradually change in a few weeks or months.
Do not discontinue the use of garden lime during this period as it may cause the hydrangeas to return to their original colors.
Do not accumulate too much lime at a time, it will inject a lot of magnesium into the soil, which will change the color of the leaves and even cause the death of the hydrangea.
Apply 25-10-10 fertilizer
In late spring or late autumn, fertilizers are distributed according to the climate and soil type according to the manufacturer’s instructions, and a layer of 25-10-10 fertilizer rich in phosphorus is applied to all plants. On the one hand, it can restore important nutrients to the soil and prevent excessive lime. The magnesium damages the hydrangea. On the other hand, phosphorus-rich fertilizers can also prevent aluminum from infiltrating into the soil and make the hydrangea change from pink to blue.
Wood ash also increases the pH of the soil. It works faster than limestone and adds potassium and trace elements to the soil. However, the concentration of wood ash is very high, too much use will greatly change the pH value and lead to nutritional imbalance. Wood ash can also “burn” leaves, so please apply it directly to the soil in winter. Apply a weight not exceeding 2 pounds per 100 square feet every two to three years, and test the soil annually.
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