There are a few different reasons why hydrangea leaves turn yellow and they’re mostly fairly easy to fix.
More often than not, hydrangea leaves will turn yellow in response to overwatering, too much direct sunlight, incorrect soil pH, or a lack of nutrients.
Let’s discuss each reason in more detail and what you can do about it.
Hydrangeas don’t like having wet feet. They need to be grown in well-drained soil that is relatively rich in organic matter.
If the leaves of your hydrangeas are turning yellow and falling off completely, overwatering or water-logged soil is most likely the reason.
When the soil is constantly wet, the roots start to suffocate because there is not enough aeration in the soil.
Once this happens, the roots will start to die and are unable to supply the plant with either water or nutrients from the soil.
How to fix overwatering
Check the soil moisture. If the soil around your hydrangeas is quite wet, you will need to either improve the drainage, if the wetness is a result of too much rain, or reduce the amount of water that you give to your plants.
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Too much sunlight
Hydrangeas that are grown in full sun and exposed to the scorching midday and afternoon sun will exhibit symptoms of yellowing and browning leaves.
So, if your hydrangea leaves are first turning yellow around the edges and then these areas start to brown and die off, your plant is likely getting sunburnt.
Hydrangeas do like some sun exposure but not too much. The morning sun is usually appreciated by these plants but in hot regions, the midday and afternoon sun is too hot.
Bear in mind though, that hydrangeas don’t like really dark areas either.
Therefore, they should be grown in areas that receive morning sun but are shaded in the afternoon.
How to fix sun scorch on hydrangeas
Provide your plants with sun protection. If you have your hydrangeas growing in an area that receives sun all day long, you’re going to have to find a way to shade them during the afternoon.
This could include erecting some shade cloth over your plants or placing larger plants in pots near your hydrangeas to give them some protection.
If the plants are still quite young, you might want to consider moving them to a more suitable spot.
Incorrect soil pH
If the soil pH is too high, it can cause chlorosis. This is where the leaves turn yellow but the veins remain green.
Chlorosis is the result of too little iron being available to the plant. This mainly happens when the soil is too alkaline as soils with a high pH tend to bind the iron and make it unavailable to the roots of the plants.
How to fix your soil pH
- Test your soil. The first thing you want to do is to test the pH level of your soil. You can get a test kit from your local hardware store. If you find that the soil pH is above 6, you need to acidify it a little.
- Add a soil acidifier or some iron chelate. To remedy the situation as quickly as possible, you can buy a soil acidifier or some iron chelate tablets that you add to the soil.
- Add compost to the soil. Incorporating compost into the soil around your plants is also a good way of increasing acidity. This has the added benefit of also adding nutrients that the plants can use. Adding used coffee grounds to the soil around your plants is another way that you can increase the acidity and hydrangeas seem to respond quite well to this.
Lack of nutrients
A lack of nutrients can be closely related to the pH of the soil but it might also be a case of not feeding the plant on a regular basis throughout the growing season.
Hydrangeas need a balanced fertiliser that has the addition of iron as well as a decent amount of nitrogen.
As mentioned above, leaves that turn yellow but have green veins are usually suffering from an iron deficiency.
On the other hand, if the lower leaves are turning yellow, then your plant might be deficient in nitrogen.
How to fix a nutrient deficiency in hydrangeas
Apply a liquid fertiliser to your plants at least once a month in spring and summer.
Use one that is specifically designed for flowering plants and ensure that it contains iron.
How do you tell if you are overwatering hydrangeas?
If the soil around your hydrangea is regularly wet or damp, it is probably receiving too much water, which can cause the roots to die. This may result in the leaves of your hydrangeas turning yellow and falling off as they won’t receive enough nutrients from the soil.
What is the best fertiliser for hydrangeas?
Use a balanced fertiliser that is specifically designed for flowering plants and ensure that it contains iron.