Causes of Hydrangea Leaves Turning Yellow & How To Fix

Hydrangeas are deciduous shrubs that boast a round mass of white, pink, blue, or purple flowers among their green leaves. 

It’s normal for these long-lasting perennial shrubs to lose their leaves in the colder months of winter only to then produce new foliage and blooms come the following spring. 

However, if you notice your hydrangea leaves turning yellow outside of this cycle, you may wonder why and how to fix it. 

Why Hydrangea Leaves Turn Yellow

Green foliage indicates your hydrangea is happy and healthy while yellow leaves indicate the opposite. 

The leaves of all photosynthetic plants get their iconic green color from a pigment called chlorophyll. This pigment is essential for absorbing sunlight, which plants will then use to make food via a process known as photosynthesis. 

If the leaves of your hydrangea are yellow, this suggests they are lacking adequate amounts of chlorophyll. In scientific terms, this is known as chlorosis. 

Numerous factors can lead to chlorosis and it can manifest in a number of different ways. It’s important to identify the symptoms specific to your plant as this will help you find the root cause and enable you to rectify the problem as quickly as possible. Here’s a breakdown of those symptoms in more detail.

Yellow Leaves Falling Off in Winter

Hydrangea Leaves

The hydrangea is a deciduous plant meaning every year it will drop its leaves in the late fall or early winter. This is part of the hydrangea’s natural cycle and prepares it for the colder months. 

Buds will start to appear in spring and your hydrangea will be in full bloom by summer. Hence, yellow and falling leaves are not a cause for concern as part of this cycle. 

Leaves Turning Yellow and Falling Off in Summer

Overwatering is the most likely cause of hydrangea leaves turning yellow and falling off during the spring and summer months. It also hinders the plant’s growth and flower production. 

Overwatering and poor soil drainage cause the soil to become saturated with water. This deprives the roots of oxygen, causing the leaves to turn yellow and drop off. 

Prolonged waterlogging can lead to root rot. Damp, anoxic conditions provide the perfect environment for a fungal infection to develop. The fungus decays the root system, slowly killing the plant which can be observed through the yellowing and falling of its leaves. 

Yellow and Drooping Leaves

Droopy, yellow leaves are often a sign you are underwatering your hydrangea. Underwatering and overwatering result in similar symptoms, so the best way to distinguish is by touch. If the leaves feel slightly crispy and the soil is dry, then underwatering is the culprit. 

Without adequate water, the plant’s cells will shrivel, resulting in droopy leaves. A water shortage also makes it hard for the roots to absorb essential minerals from the soil, impairing photosynthesis, and leading to chlorosis. 

If the climate has been particularly hot and dry, or the soil does not easily retain moisture, then your hydrangea will be especially vulnerable to underwatering.

Yellow Leaves with Brown Edges

Brown leaves on your hydrangea especially around the edges and when preceded with yellow leaves, are most likely suffering from overexposure to sunlight. Hydrangea leaves are sensitive to desiccation from harsh heat and light. Yellow and brown leaves combined with a brittle texture have been scorched. 

Foliage Turning Yellow and Flowers Changing Color

Yellow leaves with pink or red blooms suggest the soil pH is too alkaline. A high pH makes it difficult for the hydrangea to absorb magnesium and iron, leading to a deficiency that results in yellow leaves. 

Hydrangeas planted in acidic soil will produce blue flowers. Although hydrangeas prefer a low pH, aggressive acidification of the soil can burn their roots, which will cause chlorosis and potential death of the plant. 

Yellowing of Leaves with Green Veins

Yellow leaves with green veins, known as interveinal chlorosis. This means your hydrangea has an iron deficiency. It affects the youngest leaves first, but a prolonged deficiency will see it spread throughout the plant. 

Iron is required for photosynthesis and chlorophyll production. A lack of iron will also hinder the growth and development of your hydrangea. Iron uptake is determined by its availability and soil pH. 

Yellow on the Outer Edges

If your hydrangea is only showing yellow on the outer edges of its leaves, this suggests a magnesium or potassium deficiency. A deficiency in the former affects the younger leaves first whilst the latter affects the lower leaves first. 

Magnesium is an essential component of chlorophyll whilst potassium is associated with maintaining cell metabolism. The uptake of these nutrients depends on their availability and the pH of the soil.

Yellow Foliage with Brown Spots

Yellow leaves with brown spots suggest either a disease or pest infestation both of which are common problems for hydrangeas.

Fungal spores primarily infect waterlogged or damaged hydrangeas with infected plants showing yellow leaves with dark lesions.  

Pest infestations such as scale, aphids, and Japanese Beetles will also manifest as yellow leaves with brown spots. These patches are dead tissue caused by pests sucking sap from the foliage. 

Causes and How to Fix

Understanding the signs and symptoms of your plant’s ill health is the first step toward its recovery. You then need to take action and remedy the problem to avoid future occurrences. For hydrangeas, the most likely causes of yellow leaves are too much or too little water, overexposure to light, insufficient soil conditions, or pests and diseases.

Watering Issues

Hydrangeas thrive in moist soil and require an average of an inch of water every week. Younger hydrangeas and those in pots will require slightly more than established, outdoor plants. 

Hydrangeas are prone to drought stress so it’s a good idea to plant them in organic matter-rich soil that allows for good drainage. This will help to conserve moisture near their roots without it becoming too soggy.

Overwatering is less of an issue for hydrangeas but can still occur. To avoid this, ensure the topsoil is dry before watering again. 

Sunlight Exposure

Hydrangeas grow best in partial shade. Locations that expose them to the morning sun and provide shade in the afternoon are ideal to avoid heat stress and scorching of leaves. Temperatures between 59oF and 72oF are ideal. 

Soil Conditions

Hydrangeas grow best in slightly acidic soil that has a pH of between 6.0 and 6.2. I recommend testing the soil pH regularly to keep your soil within this pH range. If your soil is alkaline, the uptake of nutrients including iron, magnesium, and potassium will be hindered.

To increase the acidity of your soil, you can mix in organic materials such as compost, coffee grounds, and mulch. A sulfur-rich fertilizer will all lower the soil pH.

Pests

Hydrangeas are highly susceptible to pests including Japanese beetles, spider mites, scale, and aphids. If left undetected, they can cause extensive damage either by sucking the sap or taking out chunks from leaves. Foliage will first show signs of brown spots which can lead to the entire leaf turning brown.

Repeated applications of insecticide sprays or neem oil will kill pests and help prevent future infestations. If you choose to wash them off using a strong jet of water be sure to choose a warm day with a strong breeze to ensure that foliage has a chance to dry off. This will help to avoid the potential for the spread of fungal diseases.

Diseases

The most common fungal diseases to cause yellowing of leaves and also brown spots are rust, Anthracnose, and Leaf spot disease.

The best way to mitigate diseases in hydrangeas is to avoid getting leaves wet when you are watering. I find that using a watering can – rather than a hose – allows for better control and a more moderate flow of water. You should also avoid cramming in too many neighboring plants as this can inhibit air circulation.

Early detection will help to control the spread of fungus on your hydrangea. Regularly check leaves – especially the underside – and stems for signs of yellowing and brown spots. Remove and destroy all infected areas, re-sanitizing your cutting tools as you work. Clear away spent leaves on a regular basis too as these are likely to carry spores.

In addition spray with a fungicide treatment regularly to prevent the further spread of disease.

Click here to take a look at How to Save A Petunia With Yellow Leaves.

FAQ Hydrangea Turning Yellow

Can yellow hydrangea leaves revert back to green?

Most of the time, it’s possible for the yellow leaves on your hydrangea to revert to their normal, healthy green. Depending on the cause of chlorosis, amending the irrigation, climate, or nutrient availability should see the leaves bounce back in no time. 
If the leaves have turned from yellow to brown or are infected with a disease then the tissues are already dead and cannot recover, so it’s best to remove them. 

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.