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Hydrangeas are incredibly popular for their blossoms because of the large pom pom shape and beautiful colors. Why all the foliage on the hydrangeas might be an understudy, the changing of colors unnecessarily can still be cause for concern especially if your hydrangea leaves are turning yellow. Yellow leaves are not only unattractive but they might be indicative of a problem severe enough that your hydrangea needs immediate help.
Natural yellow color
Hydrangeas typically have green leaves but in some cases they could turn yellow. There are very few hydrangeas that have been bred to produce yellow leaves as they age. The Lemon Daddy, for example, will turn yellow as it ages so be cognizant of the variety you have so that you can be prepared for what situations warrant natural yellow color. There are also certain varieties that will turn yellow in the fall.
Now most people know that if the plant leaves start to wilt it’s indicative of dehydration, something that can be easily rectified. But if you see your leaves start to wilt and then turn yellow it could be Leaf Scorch. This is likely the case if the leaves on top of your hydrangea and on the sides would receive the most sun or the ones turning yellow with brown tips.
If this happens you will need to provide better shade especially in the afternoon. If you can’t do that make sure to water the hydrangea longer than your regularly would and verify that the soil is not to dry on a regular basis. You can also help to insulate the soil to retain moisture by applying approximately 4 inches of mulch around your hydrangea.
Leaf spot is a fungus that makes an appearance on hydrangea now and again. It’s most prevalent during the rainy weather especially as the weather itself turns warmer. If you see the leaves turning yellow that means the disease has reached an advanced state. You will probably notice smaller purple spots in the middle of summer which eventually turned gray. By the end of the summer, the leaves might even turn yellow.
You can prevent this disease from spreading by removing any fallen leaves or yellowing leaves on the plant. Make sure to also water the hydrangea at the soil level and not on top of the leaves. If you do that it can leave the plants susceptible to water retention on the leaves themselves which can cause them to openly except bacteria.
If the situation is advanced enough that it is destroying a great deal of your plant it is recommended that you use a fungicide but again only if the issue persists. You can purchase pre-mixed fungicide products and conveniently treat the issue but if you do so, follow the instructions carefully. As a general rule, you should only spray in the springtime and make sure that it covers the entire plant and don’t spray plants in sunny weather as this can burn the leaves.
Big leaf varieties of hydrangeas might have iron chlorosis which is effectively a nutrient deficiency it just means that your hydrangea is not getting adequate amounts of iron. If your leaves are starting to turn yellow and they have green veins in them even in brand new plants, it might be a problem with iron chlorosis.
You can add chelated iron to your soil, again following any instructions on the label, and this will help to treat the problem. When you pour the mixture onto the plant always make sure that you pour at the soil and not on top of the leaves. If the problem continues the soil pH could be very high so you can lower the soil pH by applying some pine bark mulch but make sure you test the levels of pH first.
If you noticed that older leaves on your hydrangea have started to turn yellow it could be a problem with nitrogen. The simplest cure is to add ammonium sulfate to the soil. Scatter this around the hydrangea at the base and then apply water. Continue to water as you normally would and this will help to increase the amount of nitrogen in the soil.