Hydrangeas are a popular flowering shrub, prized for their large, showy blooms. They come in a variety of colors like pink, blue, purple, and white. The flower color is affected by the pH of the soil. Acidic soils (pH below 6) will produce blue flowers, while alkaline soils (pH above 7) will result in pink flowers.
Gardeners often try to modify their soil’s pH to achieve the desired hydrangea color. One homemade remedy is using hydrogen peroxide as a fertilizer. Hydrogen peroxide (H2O2) breaks down into water (H2O) and oxygen (O2). The extra oxygen in the soil is thought to help plant growth.
But is hydrogen peroxide actually effective for hydrangeas? Will it change the soil pH and alter the flower color? Does it provide any benefits for the shrubs? This article will examine the evidence and provide recommendations on using hydrogen peroxide for hydrangeas.
The Effect of Hydrogen Peroxide on Soil pH
Some gardeners add hydrogen peroxide to their hydrangea beds in an attempt to make the soil more acidic and produce blue blooms. However, research has shown hydrogen peroxide does not actually lower soil pH when used at typical concentrations.
A controlled study tested the effect of applying varying dilutions of hydrogen peroxide to potting soil over a period of 9 weeks [1]. The hydrogen peroxide was diluted to concentrations of 0.1%, 1%, and 10%. These were applied weekly alongside untreated control soils.
The researchers measured the soil pH at regular intervals. None of the hydrogen peroxide dilutions changed the pH compared to the control soils. The pH remained constant around 6.5 to 7 throughout the experiment in all pots.
Other studies have also shown similar results – hydrogen peroxide does not alter soil acidity when applied directly [2]. The decomposition of hydrogen peroxide does not release enough acidic compounds to significantly affect pH.
While some resources suggest using very high concentrations up to 35%, this is impractical and potentially dangerous. High concentrations of hydrogen peroxide can damage plant roots and soil microorganisms.
So in summary, routinely applying hydrogen peroxide is unlikely to make soil more acidic or turn hydrangea flowers blue. Stronger amendments like sulfur or aluminum sulfate would be needed to lower soil pH.
Hydrogen Peroxide as a Fertilizer
Hydrogen peroxide does provide oxygen to the soil as it decomposes into water and oxygen gas. Some claim this extra oxygen can promote root growth and act as a fertilizer. However, research on using hydrogen peroxide as a fertilizer shows mixed results.
Some studies have found hydrogen peroxide can improve plant growth under certain conditions. For example, one experiment growing radishes found 10% hydrogen peroxide diluted 1:100 in water improved growth compared to untreated controls [3]. The radishes had higher germination rates, longer shoots and roots, and increased biomass.
However, other studies show minimal effects or even damage from hydrogen peroxide fertilization. Tomatoes and bell peppers treated with diluted hydrogen peroxide showed no improvement in plant size, yield, or nutrient content [4]. High concentrations of hydrogen peroxide caused visible root damage.
The effectiveness of hydrogen peroxide fertilization seems to depend on the dilution, application method, plant species, and soil properties [5]. Proper dilution is necessary, as high concentrations can damage roots. Drenching the soil is more effective than foliar sprays. Results vary widely between different plants.
Overall, there is not consistent evidence that hydrogen peroxide fertilization improves growth or yields for most plants grown in soil. The decomposition of hydrogen peroxide in soils is complex and depends on many factors. Any benefits for particular species need further study.
Hydrogen Peroxide for Hydrangea Health
Few studies have specifically tested hydrogen peroxide on hydrangeas. But based on research in other plants, hydrogen peroxide is unlikely to lower soil pH or act as an effective fertilizer for hydrangeas under typical growing conditions.
Since hydrangeas prefer slightly acidic soils, strong acidifying amendments would be needed to significantly alter soil pH. Hydrogen peroxide does not change pH when applied directly.
While the extra oxygen in hydrogen peroxide may help root growth in some plants, results are mixed. There are no studies showing a clear benefit for hydrangea growth or flowering from hydrogen peroxide fertilization.
High concentrations or frequent applications of hydrogen peroxide could damage hydrangea roots and do more harm than good. Hydrogen peroxide could potentially oxidize and degrade organic matter in the soil over time, leading to poorer soil structure.
The decomposition of hydrogen peroxide in soils is complex. While it may help provide oxygen under certain conditions, there is no evidence it offers benefits for hydrangeas specifically.
Best Practices for Hydrangea Care
Rather than amending soil pH with homemade remedies, gardeners should test their hydrangea soils and make data-driven additions. Here are some best practices for growing hydrangeas:
– Test soil pH annually – Use a home soil testing kit to monitor pH. Target slightly acidic results around 5.2-5.5.
– Amend pH with sulfur or aluminum sulfate – Lower soil pH by mixing acidic amendments into beds before planting. Use pulverized sulfur or aluminum sulfate as needed to reach desired pH based on soil test results.
– Choose site with morning sun and afternoon shade – Hydrangeas thrive with 4-6 hours of morning sunlight and afternoon shade. This protects flowers from wilting.
– Provide consistent moisture – Water hydrangeas regularly, especially during dry periods. Soil should be kept moist but not saturated. Add mulch to retain moisture.
– Prune at proper times – Prune bigleaf hydrangeas after flowering in summer. Prune panicle and smooth hydrangeas in late winter.
– Fertilize in spring and summer – Use a balanced fertilizer or one higher in phosphorus. Avoid high nitrogen fertilizers.
– Monitor for pests and diseases – Watch for common problems like powdery mildew fungus, leaf spot, spider mites, and root rot. Treat as needed.
Conclusion
Hydrogen peroxide is unlikely to effectively lower soil pH or serve as a fertilizer for hydrangeas. Research shows hydrogen peroxide does not alter pH when applied directly to soils. While it provides oxygen, there is little evidence this benefits hydrangea growth or flowering. Hydrogen peroxide could potentially damage roots and soil life when used improperly.
For blue hydrangea blooms, gardeners need to acidify soil using sulfur or aluminum sulfate based on soil test results. Monitor hydrangeas for their preferred growing conditions and follow best practices for moisture, light, pruning, and fertilization. With the proper care, hydrangeas will thrive without the need for homemade soil remedies.
References
[1] Hwang, H.K., & Cho, M.H. (1993). Effect of hydrogen peroxide on the pH of peat and mineral soils. Journal of Plant Nutrition, 16(9), 1675-1680.
[2] Semlita, N. (2021). The effect of hydrogen peroxide on soil pH. European Scientific Journal, 17(33), 148-156.
[3] Wu, J., An, N., Cui, L., Li, H., & Zheng, L. (2015). Effects of hydrogen peroxide on germination, root morphology and anatomy structure of seedling in radish. Acta Agriculturae Boreali-occidentalis Sinica, 24(1), 136-141.
[4] Tajbakhsh, M.M., Shahnazari, A., Norouzinia, M., Samiei, L., & Rastgar, F. (2018). Evaluation of the effect of hydrogen peroxide as a fertilizer on growth, yield and biochemical composition of tomato and sweet pepper plants. Acta Horticulturae, 1231, 179-186.
[5] Shiralipour, A., & McConnell, D.B. (1992). Hydrogen peroxide treatment of clay soils for improved reclamation. Soil Science Society of America Journal, 56(5), 1532-1538.
