Epsom salt can be used to turn hydrangeas blue, but there are a few things to keep in mind. The key factors that determine hydrangea color are soil pH and aluminum availability. Epsom salt affects both of these factors, making it useful for turning hydrangeas blue under the right conditions.
The Quick Answer
Yes, Epsom salt can turn hydrangea flowers blue, but only when used properly. The aluminum in Epsom salt helps lower soil pH, making aluminum more available to the plant. This causes the flowers to turn blue. But over-application of Epsom salt can damage the plant, so it’s important to use the right amount.
What Makes Hydrangeas Turn Blue
Hydrangeas can produce flowers in different colors, mainly pink, blue, or purple. The deciding factors are:
- Soil pH – Blue flowers are produced in more acidic soil with a lower pH, around 5.2-5.5. Pink flowers occur in more alkaline soil with a higher pH of 6.2-6.7.
- Aluminum availability – Aluminum causes the flowers to turn blue. When aluminum is freely available in acidic soil, it is absorbed by the plant and turns the flowers blue.
Therefore, to get blue flowers, the soil needs to be acidic to release aluminum for the plant’s uptake. Epsom salt helps with this process.
How Epsom Salt Lowers Soil pH
Epsom salt contains magnesium and sulfur compounds. When dissolved in water and applied to soil, these compounds break down into magnesium, sulfur, and oxygen.
The magnesium does not affect pH. But the sulfur combines with water and oxygen to form dilute sulfuric acid. This acidifies the soil, lowering the pH. A more acidic soil releases aluminum, allowing it to be absorbed by the hydrangea’s roots.
Proper Application of Epsom Salt
To turn hydrangea flowers blue with Epsom salt, follow these tips:
- Test the soil’s pH first, it should be around neutral 6.5-7. Acidic soil likely already has enough aluminum.
- Water the plant the day before applying Epsom salt so the soil is moist.
- Mix 1 tablespoon Epsom salt per gallon of water. Dissolve it fully before use.
- Slowly pour the solution over the soil around the hydrangea. Avoid getting it directly on the leaves.
- Repeat every 2-4 weeks in the early growing season while the plant is producing new growth.
- Check the soil pH periodically, aim for around 5.2-5.5.
- Reduce frequency if the leaves start yellowing, indicating excess acidity.
It may take a few seasons of Epsom salt applications to significantly lower the soil pH and produce blue blooms. Be patient and keep adjusting the amount used based on the plant’s response.
Why Too Much Epsom Salt is Harmful
While Epsom salt is beneficial in moderation, too much can start hurting the hydrangea. Using excess Epsom salt can:
- Burn the roots and leaves – High concentrations of magnesium and sulfur compounds can essentially “burn” the plant.
- Prevent nutrient absorption – Excess magnesium blocks the uptake of calcium, manganese, and iron.
- Cause foliar yellowing – Lack of iron causes leaves to turn yellow or chlorotic between the veins.
- Accumulate toxic levels of aluminum – Very acidic soil dissolves aluminum to toxic concentrations.
Therefore, it’s important to use Epsom salt sparingly and check for signs of over-application. Reduce or stop usage if the hydrangea shows damage.
Other Acidifying Options
In addition to Epsom salt, some other amateur and natural options can acidify soil gradually to produce blue hydrangeas. These include:
| Method | How It Works |
|---|---|
| Coffee grounds | Decomposing coffee grounds release organic acids to lower pH. |
| Composted pine needles | Pine needles break down into acidic compounds. |
| Sulfur powder | Elemental sulfur produces sulfuric acid when exposed to soil moisture. |
| Iron sulfate | Adds iron while sulfur component acidifies the soil. |
| Vinegar | Contains acetic acid, but can easily burn plants if over-applied. |
| Cottonseed meal | Releases malic and citric acid as it decomposes. |
These organic methods may take longer to significantly lower pH but are generally gentler on the plant. Monitor soil pH and the plant’s condition no matter the acidifying agent used.
Using Soil Amendments to Raise pH
If the hydrangea flowers become too blue or the leaves turn yellow from the soil getting too acidic, you can raise the pH back up by adding soil amendments. Here are some common options:
| Amendment | How It Works |
|---|---|
| Crushed limestone | Calcium carbonate neutralizes acidity and releases calcium and magnesium. |
| Wood ash | Contains high levels of calcium carbonate plus potassium. Best applied in fall. |
| Bone meal | Calcium phosphate increases pH while providing phosphorus. |
| Dolomitic lime | Calcium magnesium carbonate, less drastic pH change than calcitic lime. |
| Calcitic lime | Pure calcium carbonate, quick but drastic pH increase. |
| Pelletized lime | Ground limestone compressed into slow-release pellets. |
Rake these amendments into the top few inches of soil. Then monitor the soil pH and how the plant responds. Target a pH around neutral or slightly acidic for pink flowers.
Conclusion
Epsom salt can be an effective, inexpensive way to turn hydrangea flowers blue. But proper dosage is crucial, as too much salt can damage the plant. Test the soil first, then make modest applications. Monitor the pH and the plant’s health, adjusting usage as needed. With careful application, the beautiful blue blooms will keep coming back!
Frequently Asked Questions
What kind of Epsom salt is best?
Look for plain Epsom salt, with the chemical name magnesium sulfate. Avoid Epsom salts marketed for bathing or that contain perfumes, dyes, or other additives. Choose the plain agricultural grade Epsom salt.
How often should I apply Epsom salt?
To start turning hydrangea flowers blue, apply Epsom salt every 2-4 weeks in the spring and early summer. You can reduce frequency to once a month after the plant starts blooming. Monitor soil pH and plant health to adjust as needed.
Should I use Epsom salt for hydrangeas in pots?
Yes, Epsom salt can also help turn potted hydrangeas blue. Use a reduced amount of 1 tsp per gallon of water applied monthly. Check the soil pH regularly since there is less soil volume. Reduce frequency if leaves start yellowing.
When should I stop using Epsom salt on hydrangeas?
Stop Epsom salt applications after the plant has finished flowering, usually around late summer or early fall. Extra applications in the fall can cause damage when the plant is no longer actively growing. Resume again the following spring.
What is the fastest way to turn hydrangea blue?
Aluminum sulfate is the quickest way to acidify the soil for blue hydrangeas. But it can easily burn the plant if over-applied. Epsom salt works more gradually and is safer for the plant. Change takes patience but prevents damage.
Additional Tips for Growing Blue Hydrangeas
- Choose a hydrangea species that can produce blue flowers, like bigleaf (macrophylla) or oakleaf (quercifolia) types.
- Ensure the plant gets some shade, especially hot afternoon sun. Dappled shade is ideal.
- Use an acidic fertilizer made for acid-loving plants, like azaleas and camellias.
- Mulch around the plant with bark, leaves, pine straw, or compost. This retains soil moisture and adds organic acids.
- Avoid excessive nitrogen fertilization, which promotes more leaf and stem growth than flowers.
- Prune immediately after flowering since next year’s flower buds emerge in late summer/fall.
- Water regularly during dry periods to keep the plant actively growing.
With the right hydrangea variety, proper care, and Epsom salt applications, you can enjoy stunning blue blooms. Be patient and let the color gradually intensify over a few seasons. The results are well worth the wait!
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