This is a guide on how to use baking soda for hydrangeas safely without damaging your plants and soil. Hydrangeas are stunning flowering shrubs that bring elegance and color to any garden.
Baking Soda For Hydrangeas
Hydrangeas have gorgeous blooms, which range from deep blue to soft pink and bright white, making them popular across temperate and tropical regions alike.
However, hydrangeas can sometimes suffer from fungal diseases, poor soil conditions, or pest problems, especially in humid or densely planted gardens.
One natural, cost-effective solution that gardeners often turn to is baking soda. But how exactly does baking soda help, and how should you use it properly without harming your plants?
In this in-depth post, I explain how to safely and effectively use baking soda on your hydrangeas, backed by practical tips and scientific reasoning.
Why Consider Baking Soda for Hydrangeas?
Natural and Non-Toxic
Baking soda (sodium bicarbonate) is a non-toxic substance that breaks down into water, carbon dioxide, and sodium salts.
It is considered safe for pets, people, pollinators, and most beneficial insects, unlike synthetic fungicides or insecticides that may pose health risks or disrupt the ecosystem.
Readily Available and Inexpensive
A small box of baking soda costs very little and is available in virtually every grocery store.
This makes it an ideal treatment option for home gardeners who want to reduce costs and avoid stocking up on expensive commercial garden sprays.
Multipurpose Use in the Garden
Beyond hydrangeas, baking soda is commonly used to:
- Control fungal issues on other plants like roses, cucumbers, squash, and tomatoes
- Clean garden tools and pots
- Neutralize acidic compost or soil patches
- Eliminate odors in compost bins or around garden beds
Gentle on the Environment
Unlike synthetic chemicals that can leach into groundwater, harm wildlife, or cause resistance in pests and fungi, baking soda is environmentally friendly when used in moderation. It does not leave long-lasting residues in soil or plants.
How Baking Soda Affects Hydrangeas
pH Buffer, Not a Strong Modifier
While baking soda is alkaline, it’s a weak base and does not have a lasting or significant effect on soil pH when used at safe concentrations.
It can slightly neutralize acidic conditions on the leaf surface or in the immediate soil solution, but it won’t drastically raise soil pH.
Hydrangea color is pH-dependent, but baking soda is too weak to trigger these color changes.
For color changes, use garden lime (to raise pH) or aluminum sulfate/sulfur (to lower pH) instead.
Effective Natural Fungicide
Baking soda creates an unfavorable environment for fungal spores. It works by increasing the pH on the leaf surface, disrupting fungal growth.
It also interferes with cell ion balance in fungi, drying them out, as well as preventing spore germination when applied preventively.
It is especially helpful when dealing with powdery mildew, a common issue in warm, humid climates.
As well as leaf spot diseases, which present as dark patches that spread on leaves. Botrytis blight, which causes petal or leaf rot
Minor Soil Impact (Temporary)
Although not a substitute for true pH amendments, baking soda applied in small amounts as a soil drench may provide temporary relief for:
- Slightly too acidic soils that affect plant nutrient uptake
- Soil-borne fungal pathogens around the base of the plant
- But its effects are short-lived and limited.
Mild Pest Deterrent (When Combined)
On its own, baking soda isn’t a powerful insect repellent, but when mixed with neem oil or soap, it may:
- Discourage soft-bodied insects like aphids, mealybugs, and spider mites
- Reduce insect egg hatching rates
- Clean sticky residues left by pests like aphids
- It works best as part of a broader pest management strategy.
Baking Soda on Hydrangeas DIY Recipes
A. Fungal Treatment Spray (Most Effective Method)
Ingredients:
- 1 tablespoon baking soda
- 1 gallon of water (preferably rainwater or filtered to avoid hard mineral interference)
- ½ teaspoon mild liquid soap (like Castile soap or unscented dish soap)
How to Apply:
- Mix thoroughly and pour into a spray bottle or garden sprayer.
- Spray the entire plant, focusing on the top and bottom of leaves, stems, and flower heads.
- Applying on a dry day with mild temperatures, early morning or late afternoon, is ideal.
- Reapply once per week or after heavy rain.
When to Use:
- At the first signs of fungal infection
- As a preventative treatment during humid months
- For plants growing in shaded, poorly ventilated areas where fungus is likely to form
B. Soil Drench for pH Buffering (Use Rarely and Carefully)
Ingredients:
- 1 teaspoon baking soda
- 1 gallon of water
How to Apply:
- Water the base of the plant using the solution.
- Apply only once or twice per season, preferably in spring or early summer.
- Do not overuse, as baking soda contains sodium, which can accumulate and damage roots over time.
When to Avoid:
If your soil already has a pH above 6.5, and if your hydrangeas are growing well and not showing signs of fungal distress
C. Baking Soda + Neem Oil Pest Spray (Optional)
Ingredients:
- 1 tablespoon baking soda
- 1 gallon of water
- 1 teaspoon neem oil
- ½ teaspoon mild soap
Application Tips:
- Spray in the early morning before bees and pollinators are active.
- Reapply every 10–14 days as needed.
- Focus on tender new growth where pests tend to congregate.
- This recipe helps deter aphids, whiteflies, fungus gnats, and spider mites.
Safety Guidelines and Precautions
Avoid Overuse
Frequent or high-concentration use can lead to sodium accumulation, which degrades soil structure and harms root systems.
Never use more than 1 tablespoon per gallon for foliar sprays or 1 teaspoon per gallon for soil applications.
Avoid Application in Direct Sunlight
Spraying during intense sun can cause leaf burn or scorching. Apply only during early morning or evening when temperatures are cooler and evaporation is slower.
Always Spot Test First
Different plants and even different cultivars of hydrangeas may react differently. Test the spray on a small section and wait 24–48 hours for signs of sensitivity.
Avoid Spraying Just Before Rain
Rain will wash away the spray and reduce its effectiveness. Allow at least 24 hours of dry weather after spraying for the treatment to work.
Can Baking Soda Change Hydrangea Flower Color?
This is a common myth in gardening circles, but the truth is more nuanced.
No, baking soda will not change hydrangea flower color significantly. Hydrangea flower color is influenced by soil pH and aluminum availability.
Baking soda’s pH-shifting power is too weak to make meaningful changes to bloom color.
How To Change Hydrangea Flower Color:
To turn blue flowers pink: Add garden lime or crushed oyster shells to raise the pH.
To turn pink flowers blue: Use aluminum sulfate or elemental sulfur to lower pH and increase aluminum availability.
Always test your soil’s pH first before making any amendments.
When Not to Use Baking Soda
Avoid using baking soda in the following scenarios:
Alkaline or Sandy Soils
Baking soda will increase alkalinity further, which can lock out nutrients like iron and manganese, leading to chlorosis (yellowing leaves).
Repetitive Use Over Time
Sodium doesn’t break down easily in soil; it accumulates and can cause root toxicity, compaction, and poor water infiltration.
Hot or Dry Conditions
Leaves sprayed during high heat may get scorched, even if the spray is mild.
On Young Seedlings or Tender Growth
Baking soda can be harsh on fragile tissue and may delay growth or cause burning.
Other Natural Remedies to Use with Baking Soda
To create a well-rounded natural care routine for your hydrangeas, combine or alternate baking soda with other gentle remedies:
Neem Oil
Great for controlling insects and fungal infections. It can be mixed with baking soda for added protection.
Compost Tea
Adds beneficial microbes to the soil and improves plant immunity. Excellent as a foliar spray or soil drench. How to make compost tea.
Apple Cider Vinegar (ACV)
Used sparingly, it can acidify soil for blue blooms. It can also counterbalance excessive alkalinity from overusing baking soda.
Mulching and Pruning
Improve air circulation and reduce fungal growth by regularly pruning and using organic mulch like pine needles or bark chips.
Final Thoughts
Baking soda is used by organic gardeners to safely control fungal diseases, support healthy foliage, and even help reduce minor pest problems when mixed with other ingredients.
However, it won’t change the color of your hydrangeas or solve every problem. For major issues like soil pH adjustment or severe disease outbreaks, consider more targeted treatments.
Used correctly, baking soda can help your hydrangeas stay healthy, beautiful, and bloom with brilliance year after year.
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