Yellow Hydrangea Leaves
Practical solutions to getting your hydrangeas back to health
Created by Daniel at DIY Gardening
Hello and welcome to another entry in DIY Gardening’s blog.
My name is Daniel, and today I will explain the most common causes of hydrangea leaf yellowing and what you can do about it.
I was contacted by a friend 10 days ago, she had a problem with one of her hydrangea plants as the leaves were a sickly yellow colour, and as it was only June, she was concerned.
I diagnosed the problem in a matter of minutes, and the hydrangea is now on its way back to health.
I hope you find my guide insightful.
In a Hurry? Here’s an Overview
Yellow hydrangea leaves are most likely caused by a deficiency in iron or magnesium (or both).
This product by Doff is fast-acting, and I’ve seen it green-up leaves in a matter of days.
It would be best if you tried to get to the bottom of why your hydrangea has a deficiency, so read the rest of my guide, where I’ll go into greater detail and offer long-term solutions. I’ll also list other, less common reasons why these leaves may turn yellow.
Most Hydrangeas are Deciduous
Most hydrangea plants are deciduous, meaning they lose their leaves annually, usually in autumn and winter.
Hydrangea leaves will typically turn yellow, brown or even an off-purple colour as winter approaches, and this is all normal.
You shouldn’t be worried about yellow leaves as winter approaches, but you will need to take action if the leaves are changing colour in the spring or summer as they should be a lush, healthy green colour at this time of year.
Does Your Hydrangea Have Yellow Leaves With Green Veins?
The hydrangea leaves shown below are showing early signs of chlorosis:
Tell-tale signs of this are:
- Yellow leaves with green veins.
- Fewer leaves.
- Smaller leaves.
- General stunting of growth.
The photo below shows a comparison between a healthy green leaf and a smaller yellow leaf, note the green veins in the smaller leaf:
Another photo showing obvious chlorosis on a new hydrangea leaf:
The leaf shown below was taken from a healthy hydrangea; note the uniform green colour across the leaf and veins.
If your hydrangea plant has yellow leaves and green veins on new growth only – this is iron deficiency, of which there are several causes so keep reading.
If the leaves are yellow with green veins but only on older established leaves – this is magnesium deficiency, and there are several causes of this too.
Give Your Hydrangeas a Boost of Iron or Magnesium
The first step to getting your hydrangeas back to health is to give them a dose of iron or magnesium, but this will only solve the problem temporarily; you’ll need to dig a little deeper to find out what caused the deficiency in the first place.
I recommend the product below, but most garden centres will stock something similar.
I’ve previously used Plant Tonic on petunias, and I saw the yellow leaves turn green in less than 5 days, so I know it works well for plants with iron deficiency.
Underlying Causes and Solutions – Iron Chlorosis
Here are the most common causes of iron deficiency, which leads to yellow leaves with green veins on new growth:
Overwatering – While hydrangeas are thirsty plants, they shouldn’t be watered so much or so frequently that the soil or compost is waterlogged. If the hydrangea’s roots are waterlogged, they won’t be able to extract iron from the soil, and chlorosis will form on new leaves. Also, excessive watering of pots and containers will flush out the iron, compounding the problem.
Lack of drainage – Another common cause of yellow hydrangea leaves is lack of drainage; while rarely an issue in most sunny borders, it affects plants grown in pots; you should make sure the pot has sufficient drainage holes.
Improper fertilisation – Certain minerals such as manganese, copper, zinc, calcium and phosphorus, can, when used in excess, prevent the plant from uptaking iron. You can test the soil for pH and nutrients to see what’s going on or dial back the fertiliser, or switch to one specifically created for hydrangea plants.
Magnesium Deficiency – Causes and Solutions
Magnesium deficiency causes yellow leaves and green veins in older, established leaves, and while it’s less common than iron deficiency, it can kill the plant if left unchecked.
Poor soil – Magnesium deficiencies often occur in plants grown in sandy, light soils. Mixing in a good quality multi-purpose compost should help.
Too much potassium – Fertilisers with a high potassium concentration (such as tomato feed) can cause problems with magnesium uptake as the hydrangea will prioritise the potassium.
General watering – As with iron deficiency, too much or too little water can cause problems as it interferes with the roots’ ability to uptake magnesium. The soil or compost should be slightly moist but not waterlogged and certainly not bone dry.
Summary of Why Hydrangea Leaves Turn Yellow
Yellow hydrangea leaves can be caused by several issues, the most common being:
- Overwatering in pots.
- Waterlogged roots in pots.
- Improper fertilisation.
All of the above can lead to deficiencies, and while iron or magnesium supplements solve the problem in the short term, the underlying cause should be addressed.
To confuse matters, hydrangeas that aren’t given enough water can also produce stunted leaves that won’t look healthy and green, but these leaves are usually shrivelled and wilted.
Deficiencies aren’t the only cause of yellowing leaves, but they are the most obvious as they only affect new/old leaves.
Another common cause is sunlight, or to be more specific, too much direct sun during the day.
The best spot for a hydrangea is one that receives morning sun but afternoon shade. Too much mid-day sun can lead to leaf burn where the leaves turn yellow, brown or off-purple.
Tell-tale signs of sun scorch are wilting leaves, brown leaves/flowers and shrivelled, stunted top growth.
Pests and fungus are often found on hydrangeas grown in crowded areas as these plants prefer space, especially near the base of the plant where it should be well ventilated.
Tell-tale signs of a pest or fungus issue are brown, red or purple spots in spring or summer.
Opening up space at the plant base, providing a good mulch and preventing overhead watering should stop pests and fungus from spreading.
Postscript: Hannah has published a delightful guide to growing hydrangeas in pots, go check it out.
More From Daniel Woodley:
This guide to solving hydrangea problems was created by Daniel Woodley here at DIY Gardening and was last updated on the 24th of June, 2021.
Discover more helpful hints and tips from Daniel over at the blog.
Daniel is a keen amateur gardener who also manages a large residential landscape and his own mid-size garden.
He also enjoys growing vegetables and fruits, as well as his herbaceous border and container garden.
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