Hydrangeas are a popular garden shrub, prized for their large, colorful blooms that can range from vibrant blues and purples to soft pinks and whites. While these classic flowering shrubs are easy to grow, getting those highly desired big, bold blooms can be tricky business. This is because hydrangea blooms are highly dependent on soil pH and proper hydration.
One commonly asked question by hydrangea growers is whether boiling water helps hydrangeas bloom better. The short answer is yes, in some cases applying boiling water to hydrangea roots and soils can help encourage bigger, more vivid blooms. However, this technique isn’t necessarily effective for all types of hydrangeas or soil conditions.
Read on to learn more about the science behind boiling water and hydrangea blooms, as well as tips for properly using this technique for the best results.
How Hydrangeas Bloom
To understand how boiling water affects hydrangea blooming, it helps to first understand what controls hydrangea blooms.
There are two main factors that influence hydrangea blooms:
Soil pH
The most important factor is soil pH. Hydrangeas absorb aluminum from the soil which reacts with the pigments in the flowers, producing those coveted blue and purple tones. However, aluminum is only soluble and available to plants at lower pH levels.
In acidic soils with a pH below 5.5, aluminum is present and absorbed, resulting in bluer blooms. In alkaline soils with a pH above 6.0, aluminum becomes unavailable, resulting in pink blooms. White hydrangeas are not affected by soil pH.
Water
The second factor is proper watering. Hydrangeas have large water needs, especially when blooming. Too little water will result in dried out, lackluster blooms. Deep, thorough watering provides hydration for luxurious blooms.
So in summary, acidic soil and abundant moisture encourage the best hydrangea blooming. This is where boiling water can sometimes play a role.
Does Boiling Water Lower Soil pH?
Boiling water does not actually lower soil pH on its own. However, the science behind why people think it works is interesting.
Here’s the theory behind boiling water and pH: boiling water releases calcium and magnesium from your water. These minerals raise pH. So when you boil water, you remove these minerals and are left with “purer” water.
This pure, mineral-free water theoretically has a neutral pH. When applied to soil, it supposedly helps leach out salts and minerals that raise pH over time. Proponents claim the use of boiling water over time therefore gradually lowers soil pH.
However, studies testing this theory did not find compelling evidence that boiled water lowered soil pH more than unboiled tap water. While pure, deionized water can lower soil pH, boiled tap water does not appear to have a significant effect.
Does Boiling Water Help Hydrangea Blooms?
While boiling water may not lower soil pH, anecdotal evidence suggests it can still enhance hydrangea blooms in a couple ways:
Loosen soil
First, pouring boiling hot water onto the roots and soil can help loosen clay soils and break up compacted areas. This improves drainage and allows roots to spread unimpeded.
Remove salts
Second, boiling water may help leach away accumulated salts and minerals left behind from tap water and fertilizers. This cleansing helps roots take in water and nutrients more efficiently.
Provide heat
Finally, the hot water adds a burst of heat to the soil, which can encourage faster growth and blooming. Think of it like a mini hot spring for your hydrangeas!
So in summary, boiling water probably won’t alter pH much, but it can still support better blooming by improving soil structure, flushing salts, and stimulating growth.
How to Use Boiling Water on Hydrangeas
If you want to test out the boiling water theory for your hydrangeas, follow these tips:
When to apply
Apply boiling water in early spring before growth starts and again in fall after blooming finishes. This avoids damaging tender roots and foliage.
Watering can method
Bring several gallons of water to a rapid boil. Carefully pour the hot water into a watering can or bucket. Apply the boiling water directly to the soil around the hydrangea, not the foliage.
Tea kettle method
Boil water in a tea kettle. Walk around the hydrangea and slowly pour steaming water directly over the roots. Be careful to avoid contact with leaves and stems.
How much water
Aim to deeply soak the root zone area but avoid runoff. For a mature hydrangea, boiling 2-3 gallons is usually sufficient.
Repeat applications
Apply boiling water twice per year for best results. Early spring and late fall are ideal times.
| Time of Year | When to Apply Boiling Water |
|---|---|
| Spring | 4-6 weeks before blooming begins |
| Fall | After blooms fade |
Other Tips for Great Hydrangea Blooms
While the boiling water technique may (or may not) help, implement these other gardening practices for surefire success:
Choose suitable cultivars
Select hydrangea species and cultivars suited for your hardiness zone and site conditions. Certain types, like bigleaf and oakleaf hydrangea, do especially well in many areas.
Plant in ideal sunlight
Give hydrangeas a site with the right amount of sun for the variety grown. Most prefer morning sun and afternoon shade.
Enrich soil
Improve clay and sandy soils with organic matter like compost or leaf mold. This creates the moist, loamy soil hydrangeas love.
Mulch roots
Apply 2-4 inches of shredded bark, leaves, straw or other organic mulch over roots. This conserves moisture and insulates roots.
Water thoroughly
Give hydrangeas 1-2 inches of water per week from rain or irrigation, allowing soil to dry slightly between waterings. More water is needed in hot, dry weather.
Fertilize lightly
Use an organic or low-phosphorus fertilizer 1-2 times per year to support growth. Avoid over-fertilization.
Control pests
Watch for common pests like leaf spot, powdery mildew, and mites. Take action early to prevent damage.
Prune properly
Prune strategically in late winter to shape plants. Remove dead stems and thin interior branches to open up plants.
Conclusion
While the science is still unsure, boiling water may be a helpful hack for increasing hydrangea blooms. The key is using it properly and pairing it with other best practices like soil prep, ideal siting, sufficient hydration, and attentive care. With the right growing conditions, your hydrangeas will thrive and give their most spectacular floral display year after year.
