The unusual color of the hydrangeas’ purple leaves could be a sign of a fungus or a simple environmental issue.
Fungal Disease
Cercospora leaf spot, a prevalent leaf fungus in these plants, can be identified by the presence of purple dots on hydrangea leaves. Although spotted leaves can shed early, weakening the plant and limiting the number of viable buds, plants are rarely killed. Usually beginning at the plant’s base, the tiny purple to brown patches grow outward and upward when water splashes the spores onto adjacent leaves. The type of hydrangea involved determines the specific spotting patterns.
By removing fallen leaves and hydrating your hydrangea at the base, you can stop cercospora from spreading. In a densely packed hydrangea bush, opening the canopy by pruning up to one-third of the branches will improve air circulation and hinder the spores’ ability to germinate. Azoxystrobin, chlorothalonil, mancozeb, myclobutanil, or thiophanate-methyl should be used at intervals of 14 days if cercospora is severe and pervasive.
Phosphorus Deficiency
When hydrangea leaves become purple, the plant may be trying to notify you that there isn’t enough phosphorus in the area to support it. In their haste to alter the hue of their hydrangeas’ flowers, gardeners occasionally unintentionally cause the pH to go so low that other chemical substances bind phosphorus. The inability of bound phosphorus to be utilized by plants deprives them of essential nutrients.
Examine your soil. Alkali soils with pH levels above 7.0 may bind phosphorus with calcium or magnesium, while acidic soils with pH levels below 6.0 frequently allow aluminum to bind the element. The initial step in releasing phosphorus from your soil is to adjust the pH, but if this doesn’t work after a few weeks, you’ll need to fertilize your hydrangea with phosphorus.
Weather’s Influence
The color of hydrangea leaves can also be affected by the weather, resulting in extensive purple discolouration. When the growing season is about to finish, cool conditions may cause the plant to go into dormancy early, allowing the purple color of the leaves to emerge as the green chlorophyll factories stop producing them for the year.
Purple discolouration might also result from frost damage. When the leaves are dry, remove the severely harmed ones, but keep the somewhat harmed ones until new leaves emerge.
How are purple stains on hydrangea leaves treated?
On shrubs that had damage the previous year, fungicide should be sprayed on fresh leaves every 10 to 14 days. As fresh leaves emerge from the plant and grow, spray them. Spray the stems and limbs, being sure to reach the underside of the leaves. If your leaf spot problem was serious, regular fungicide applications may be able to eliminate it.
Does the color of hydrangea leaves change in the fall?
When there is a sharp and fast shift in temperature, when there is a fungal illness, or when the plant is deficient in some nutrients, hydrangea leaves turn purple.
Here is a description of each:
Frost Damage
Hydrangea leaves may become purple due to a springtime late frost. However, the weather need not be frigid; even cool autumn weather can cause the leaves to become purple.
The plan’s dormancy period may begin sooner as a result of this temperature change. In addition, changes in light conditions may prevent chlorophyll from being produced, discoloring the leaves.
By providing winter cover for your hydrangeas, you can reduce the risk of frost damage, though erratic weather can still negate your efforts.
Unfortunately, frost can also harm freshly developed buds, preventing a good flowering season.
Frost damage is one of the more challenging causes of purple-tinged hydrangea leaves to avoid, unless you currently use it as a winterization technique or have access to a protective cover.
Fungal Disease
Hydrangea leaves frequently develop fungal infections. Purple patches are typically a sign of cercospora leaf spot, a fungus-related illness.
Making every effort to reduce your risk of contracting the disease is your best defense against it because it spreads by spores and is challenging to control an ongoing infection.
Cercospora leaf spot typically begins at the plant’s base and progresses upward if water droplets transport the fungus’ spores to other sections of the plant.
However, they can also be dispersed by the wind or by improperly sanitized pruning scissors used to trim your hydrangeas.
Cercospora leaf spot on hydrangeas can cause the following problems in addition to its cosmetic drawbacks:
- Purple-spotted leaves may drop off early.
- cuts down on viable buds
- The plant’s natural defenses may be weakened.
Fortunately, there are a number of things you may take to slow the disease’s progress or even stop it completely:
- Hydrangeas should always be watered from the base to avoid watering the foliage.
- Eliminate clutter and fallen leaves that could contain spores and spread them when contacted by raindrops or other liquids.
- By cutting densely populated bushes, air circulation around and inside the shrub will be increased. The germination of spores will be inhibited by good air movement.
- Spray fungicides on the plant at intervals of 14 days to treat a severe and pervasive cercospora leaf spot disease. Fungicides with chlorothalonil, azoxystrobin, mancozeb, thiophanate-methyl, or myclobutanil are good options.
- To prevent the spread to additional stems or other shrubs, remove the afflicted plant parts.
It is best to adopt preventative measures and even spray hydrangea leaves with organic fungicides like neem oil at the very first signs of the disease, or even simply as a simple precaution, because fungal diseases can acquire resistance to chemical pesticides.
Nutrient Deficiency
If none of the aforementioned issues exist—that is, there was no frost or indication of a fungal spot disease—the fact that hydrangea plant leaves turn purple could indicate a nutritional shortage.
A phosphorus deficit is most frequently to blame for the purple coloration of the leaves. A pH imbalance in the soil might lead to a phosphorus deficit.
In order to make their hydrangea blooms blue, gardeners frequently unbalance the pH of their soil.
You must acidify the soil in order to make hydrangea blossoms blue. Gardeners can use one of the several soil acidifiers available for this purpose.
However, excessive acidity can lead to chemical phosphorus binding, which prevents plants from receiving it.
Therefore, you don’t need very acidic soil for your hydrangea to produce blue blooms; only a little bit of acidity will do.
You can check your pH level to make sure you aren’t over-acidifying your hydrangea plants and causing their leaves to become purple.
The pH balance can be restored by amending a severely acidic soil, but it will take several weeks for your hydrangeas to notice the change.
Additionally, you must fertilize your hydrangea with a phosphorus-rich fertilizer. In order to avoid overfertilizing the plant, be careful to adhere to dose guidelines.
Anthocyanin Pigments
Hydrangea leaves typically turn red because anthocyanin pigments are produced in the leaf cells. These pigments are produced by plants in response to a variety of stresses, such as temperature extremes, excessive or insufficient light, and pest attacks.
Over 600 different types of anthocyanins are found in nature, and researchers are still trying to figure out exactly how they defend plants.
According to studies, they boost the efficiency of photosynthesis, operate as a form of sunscreen against damaging UV rays, and serve as antioxidants that protect against free radical damage.
Solution
Making sure that plants don’t suffer any stress is the only way to avoid them from developing anthocyanins. This entails planting hydrangeas in rich, well-draining soil, giving them regular water without drowning them in it, and positioning them so that they receive morning light but enough of shade throughout the hottest part of the day.
They don’t require feeding if they are grown in the ground, but they will benefit from a compost mulch once a year. In containers, hydrangea-specific slow-release fertilizer that is used once a year is a suitable choice.
Cold Weather
Hydrangea leaves typically become crimson as the temperature drops before falling off the plant. This occurs naturally as part of the life cycle and is typically unimportant.
There are deciduous hydrangeas. This implies that their leaves drop off in the fall and then sprout in the spring. A deciduous plant becomes dormant throughout the winter, which means it doesn’t grow or need as much water or nutrition.
The chemical that gives plants their green color, chlorophyll, is produced less by deciduous plants’ leaves before they fall off the plant and more by anthocyanins.
As a result, more orange and red hues are visible as the chlorophyll deteriorates. This makes it possible for leaves that are close to dying to keep producing as long as they can.
Your deciduous hydrangeas will lose their leaves in the winter, but as long as the temperature doesn’t dip below 0 F, they can stay outside unprotected (-17.7 C). They will develop new growth in the spring, and it will be green, not red.
Some varieties of hydrangeas are evergreen, which means that plants won’t turn red and lose their leaves over the winter. Try the climbing Hydrangea integrifolia or Hydrangea seemanii if you’d like a plant with lush green leaves all year long.
Growing In Full Sun
The optimal conditions for hydrangea growth are direct sunlight during the chilly morning hours and afternoon shade.
Your plant will produce anthocyanins, which make the leaves red, to defend itself if it is exposed to direct sunlight all day.
Although they are harmless and serve to shield the leaf cells from harm, these pigments are a clue that the plant is not in its ideal environment.
Make careful to place your hydrangea where it receives morning sun but not afternoon sun. Some varieties require more or less sunshine than others, with the majority preferring roughly 46 hours every day.
If you are unable to transfer the plant, think about how you can give it some shade during the warmest time of the day. To offer cover, you could plant additional trees or shrubs or construct a building like a fence.
Lack of Light
As anthocyanins can enhance cells’ capacity for photosynthetic activity, hydrangeas growing in an overly shaded location may also develop crimson leaves. Therefore, if your plant is becoming red and only receives four hours or less of sunlight each day, this may be the problem.
Lack of light frequently results in pale growth that slants toward the nearest source of light, or occasionally a mix of pale and red development.
Verify that your plant is receiving adequate sunshine. If it is completely shaded, you should move it to a brighter location while making sure it is not directly in the sun.
If you are unable to transfer the plant, think of creative ways to enhance the amount of morning light it receives, such as by pruning adjacent trees and bushes.
Since hydrangeas are not heavy feeders, over fertilization may reduce the amount of flowers produced by the plant or possibly harm its roots. However, it’s a symptom of phosphorus insufficiency if you see that your plant’s lower leaves are becoming purple from the tips.
One thing to keep in mind is that Hydrangeas have trouble absorbing phosphorus when soil temperatures go below 55F (13C).
Wet soil exacerbates this issue and makes it challenging for the plant to absorb nutrients. Maintaining your plant in a well-draining environment is crucial.
You shouldn’t be concerned about the soil temperature in the fall and winter because most varieties of hydrangea go dormant in the winter and don’t need to absorb nutrients.
When planting your hydrangea, use a lot of high-quality compost, and cover it with compost once or twice a year. All the nutrients a plant requires are present in compost in a readily utilizable form.
You usually won’t need fertilizer unless your soil has a severe nutrient deficiency. If you do decide to use additional fertilizer, use one made specifically for hydrangeas and only use it once or twice a year, as directed.
Underwatering
The Greek words for water (hydros) and jar are the origin of the name “Hydrangea” (angos). You should now have a general notion of the plant’s water needs!
Although they dislike soggy soil, hydrangeas do require a lot of moisture. Even the most seasoned gardeners may find this to be a challenging balance!
It may be an indication that your plant needs more water if you see the leaves of your plant drying up, curling, and turning red.
But be cautious—before you increase the watering, check to see whether the plant has root rot, which can also manifest as dehydration symptoms.
This issue is simple to fix if you’ve established that the plant doesn’t have root rot. Just add more water to your plant!
You’ll most likely need to water twice or three times per week during the heat. To aid the soil in holding onto water, think about applying hardwood mulch.
Because hydrangeas dislike having moist feet and are susceptible to root rot, the soil must be well-draining. Reduce watering over the winter and only water the soil if it is entirely dry.
Xanthomonas and CercosporaLeaf Spot
It can be Xanthomonas or Cercospora leaf spot if you’ve seen red or purple spots on your Hydrangea that are slowly spreading from the lower leaves.
Xanthomonas and Cercospora are bacterial and fungal diseases, respectively, yet they share many of the same symptoms. Once established, they can be very difficult to treat because they spread through diseased organic debris.
However, these infections can also spread through equipment or even on your hands. Usually, bacteria or spores spread from infected substances to plants through splashing water, such as rain or when plants are watered from above. (Source: Extension Service of Michigan State University)
By clearing away fallen leaves and other decaying organic debris from the area around the plant, you can try to avoid both of these illnesses. By ensuring that there are few hiding spots for bacteria or fungal spores, infection risk will be decreased.
AXANTHOMONAS infection is difficult to treat once it has been established. The only thing you can do is remove the contaminated plant portions and hope for the best since there are no efficient bactericides on the market.
While some plants manage to withstand the infection, others cannot. The plant should ideally be destroyed if the infection is extremely serious.
If you detect Cercospora leaf spot early enough, fungicide can be used to treat it successfully. The plant has a decent chance of surviving if less than 20% of it is affected.
It’s usually best to eliminate badly affected plants and try again. Be careful not to reuse plant-infected soil or containers without properly disinfecting them.
Phytophthora Root Rot
The root rot fungus, Phytophthora, thrives in moist soil and is easily spread by splashing water or contaminated soil.
It kills all plants, but because Hydrangeas need a lot of water, it can be especially difficult while cultivating them. Your plant is more likely to get root rot if it is in wet soil.
Dehydration symptoms are typically brought on by root rot, which inhibits the plant from absorbing water through its roots. Root rot may be the problem if your plant’s leaves are drooping, dry, or reddening while receiving plenty of water.
Always ensure that the soil where your hydrangeas grow has good drainage. Never let it stand in soggy soil for an extended period of time. If the area becomes flooded, think about moving the plant or enhancing soil drainage.
Root rot is particularly difficult to treat after it has established itself. You can attempt by pulling out any infected roots—which will seem brown and slimy—replanting in drained soil, and waiting a while before watering.
The plant could survive. It may be preferable to remove the plant and try again because root rot is often the end of many plants.