When it comes to answering why the leaves of jasmine plants are turning red, we need to think of two different scenarios: First, why are my Star jasmine's leaves turning red? Or second, more generally speaking, why are my other jasmine plants' leaves turning red?

Red leaves on a Star jasmine
This jasmine plant's leaves have turned red

Whilst most of the jasmine plant varieties will keep their foliage evenly, in terms of deep green color throughout the growing season, some plants may suffer some issues related to a disease or nutrient deficiencies that will cause their foliage to turn into a deep red color. We detail all of these down below

However, there is an exception to this which is goof to know about. That exception is the Confederation jasmine plant, which is also known under the name Star jasmine. Their leaves will naturally turn into a deep red or even maroon color by the end of the year or growing season. This is a normal phenomenon for our Star jasmines and it is not cause for concern, rest assured.

The Confederate or Star jasmine Tricolor plant variety will have pink to deep red colored leaves, even from when the plant is young and as the plant matures, it will start changing into an intense green with white dots on the surface of its leaves.

Even in adult plants we observe red leaves, following the climatic changing conditions during the year (within a normal range of temperatures). This usually happens at the end of the year, its leaves could also turn into a deep red tone again. However unlike other jasmine plants, the foliage will be maintained through the year and won’t lose the buds until new leaves appear.

All is likely fine if your Star jasmine has red leaves, it is even expected. Let us discuss other jasmine plants next.

What are the reasons why your jasmine plants' leaves are turning red?

Here, we cover what reasons could cause jasmines other than Star jasmine to have red leaves. Common causes include temperature, nutrient deficiencies, a pH imbalance of the soil, a disease, too little water and finally fungal infections. We are going through these one by one.

Cold Temperature

Most commonly in spring, cold temperature could be a cause for red leaves. Let's assume it is early spring and the nights are getting kind of cold, not close to the freezing point, but they are getting a bit cold, coming off the winter period, maybe dipping down to the low 40s to 50 °F (4 to 10 °C) temperature and your jasmine doesn’t like that. See, jasmines are tropical or sub-tropical plants and therefore like warm and humid conditions most of the time. They are quite sensitive to growing conditions and temperature is one of the most important ones.

Thus, cold temperature is one of the most common environmental stress factors when it comes to leaf preservation and survival mode, both in terms of shape and color. Jasmine plants respond to temperature stress by shutting down or reducing the energy expenditure to face the colder weather where the photosynthesis process is not as efficient. Think of this as the plant's way of battening down the hatches.

As the weather gets a couple of degrees warmer again, closer to what the jasmine likes, the cold stress will normally pass and in a short period of 2 to 5 days the leaves will usually. turn back to green again.

A nutrient deficiency

There could be other reasons than temperature, why your jasmine's leaves are turning red and these may require some intervention on your part to fix them, such as a nutrient deficiency. Normally, the most common nutrient deficiency is low phosphorus. Whilst phosphorus is involved in root and flower development, a lack of phosphorus or a deficiency in phosphorus can manifest itself in the leaves, especially if it goes on for a prolonged period of time. That's quite unlike a nitrogen deficiency, which usually wouldn't cause leave reddening.

So one of the tips to fix this is to start adding a little bit of fertilization which is higher in phosphorus around the time in late summer or very early fall as the summer is coming to an end. This way, we set up our plants for the winter.

There are a couple of different products you can use for dealing with a phosphorus deficiency.

  1. Bone meal is the perfect example of a great fertilizer high in phosphorus. A little bit goes a long way, you don’t want to overcompensate by adding too much of it otherwise the pH will increase too much over time causing your plant to have other issues and maybe even die in an extreme case of overuse.
  2. If you wish to not go for an animal product fertilizer, then you can use an alternative like all purpose rock phosphate.
A very red jasmine plant
Jasmine plant with red leaves, which can be caused by a lack of phosphorus.

A pH imbalance of the soil

A pH imbalance of the soil is very common especially in the early spring when we are re-making the soil beds, perhaps adding a little bit of lime, wood ash or adding a new compost which is a bit more acidic or the new beds have a bit too much of clay content. Then the soil pH can become a bit imbalanced, becoming too acidic or too alkaline. Too much acidity or alkalinity will cause your plant not to uptake the nutrients. Your new bedding might have all the required nutrients but because your plant can’t absorb and process those nutrients as efficiently as it should, we again face a nutrient problem, albeit a different kind as before.

You can prevent pH issues and test this frequently by purchasing a pH strip, which is very easily accessible online from any lab provider involved in swimming pool pH testing and what not.

Very easily, grab a little bit of the soil/bedding, mix it with a bit of water and stir it up and then dip in the pH strip test and compare it to the color bar in the package to measure your soil pH. There you go, you can easily figure out if your soil is too acidic or too alkaline.

If the soil turned out to be alkaline, don’t freak out. All you need to do is to acidify it a bit by adding small amounts of elemental sulfur, aluminum sulfate or dilute sulfuric acid (be careful with sulfuric acid, and only use it if you are comfortable with acids. Always observe the required safety procedures like eye protection and gloves and use acids dilute only, never concentrated. If you don't know how to safely handle acids, it's better of you don't use them until you do). With this measure, you want to go light on. Aluminum sulfate comes dissolved in water at a pH of 2. A dilute solution of sulfuric acid can be used as is or diluted down further. Elemental sulfur would be added to the soil directly in low quantities.

Pour a little bit of the acidic liquids sulfuric acid or aluminum sulfate (about a cup's worth) into a big bucket of water (like a gallon), mix well and then add that water over the soil around your plants for a fast acting source of acidity which will lower the soil pH. If you're in doubt of how much that will do to the acidity of your soil, proceed slowly using parts of the bucket of water first and periodically remeasure the pH as mentioned above and see if you need to repeat the procedure. We are aiming for a value of 6.5 to 7, which is slightly acidic or neutral.

You could also add a new compost with a pH 7 too your soil which, again, its about what we are after, it will neutralize the alkaline pH of that soil. Remove some of the soil and mix it into new neutral soil, measure that pH again and add it back to your plant if the value is appropriate, between 6.5 and 7.

A side note here: Bone meal only works well under somewhat acidic conditions, therefore make sure that your pH stays below 7 if you are using bone meal to increase phosphorus. Here, it's best to go for 6.5 pH.

A disease

Although there could be a couple of diseases affecting your plant, the most common one that would result in red color leaves, is known as root-knot nematode. Root-knot nematodes are a very small (0.03 inch or 0.75 mm) and colorless roundworms from the Meloidogyne hapla and Meloidogyne incognita species.

These nematodes are a parasite that exists in the soil and loves humidity and moist places. So what happens is, that the nematode larvae will infect the roots of your jasmine plants, it will create knot galls and it will drain your jasmine plant from its nutrients. Not only will the leaves start turning red but also the flower yield will dramatically plummet if there's a nematode issue.

Essentially, this, will represent itself in the form of a lot of root knots (galls) at the bottom of the plant. When you pull your plant out of the soil, the roots will look like a ball of knots. What happens is that the roots will get all obstructed and soggy and that will stop the plant's natural processes of up-taking the required nutrients. And once again, phosphorus will be the main nutrient to be affected by this disease.

How do we treat a root-knot nematode infection?

We need to get rid of the parasites and there are two organic nematicide products available to you that are easy to access which will reduce the nematode populations. The first product is based on the essential oil geraniol and the second one is based on saponins from Quillaja saponaria the soapbark tree.

Aside from these two, you can also use azadirachtin extracted from neem oil. This is a pretty good remedy for early stages of these nematodes, as it is pretty light nematicide, very effective though and it also works against other parasites and mites.

You could also add a little bit of neem seed meal to your jasmine plant soil, as a gentle fertilizer helping out by strengthening the soil bed

There is one more solution available that is highly effective in eradicating root knot nematodes. This product are black walnut hulls, which are high in juglone, a natural chemical that will get rid o those nasty nematodes. Simply add a layer of compost of those smashed walnut hulls to your jasmine plant bedding soil.

Jasmine plant infected root-knot nematode
Jasmine plant infected with root-knot nematode

It is said that an ounce of prevention is worth many pounds of the cure and when it comes to preventing root-knot nematodes practicing good crop rotation is key. Planting crops like marigolds or Sudan grass between your jasmine plants, will dramatically reduce the root-knot nematode population in the soil, because marigold secrets a nematode-killing agent from its roots.

The following points are essential to keep in mind when it comes to prevention of this disease:

  1. Clean the roots of old plants.
  2. Till the soil
  3. Add more organic material to your soil

A lack of water

It has happened to all of us: Maybe we have been away for too much time without previously properly preparing our jasmine plants by watering them thoroughly. Or maybe our friend forgot to show up and water our garden as was agreed upon while we were traveling. Maybe it has suddenly gotten really dry for a couple of days or weeks and the plant is now not receiving the required amount of water. The result is the same: The soil dried up quickly and the leaves will also start to dry and then turn red as a result.

So it is super important that you prevent this by simply sticking your finger in the soil to make sure it is moist enough or by maybe getting yourself a humidity probe, which is available for purchase on-line. Just remember that the soil shouldn’t get too compact and too humid, as jasmine plants don’t like that and the roots will rot and won’t survive long.

If you return from a trip and find a dry up jasmine with red leaves, make sure to water it thoroughly and regularly without over watering. Make sure the soil drains every time and that there is no standing water.

A fungal infection

There are a couple of fungal infections which could cause your jasmine plant's leaves to turn red.

Pythium and Rhizoctonia

Pythium species affect mainly the roots of the jasmine plant and Rhizoctonia affect all parts of the plant. But essentially, these fungi species love moist and wet conditions to spread out. As we were mentioning above, poor drainage in the soil, reduced air convection and over-watering (which could be standing water from heavy rain or over irrigation) will promote rotting diseases in the roots. These infected roots will soften and darken and will lead to the growth of new shots in a distorted way with a brown and red lifeless color.

Therefore, to begin with, improving the soil drainage is crucial. So you can start with removing part of that wet soil and replace it with new soil, for a period of time to allow the roots to dry. Also, you should prune those deep red leaves to avoid the fungal infection to spread out across the plant and help improving air circulation.

Finally, to top it all up, you can spray the plant with the appropriate fungicide against Pythium and Rhizoctonia, to prevent the fungal infection from spreading out more.

Jasmine plant leaves turning red due to a fungal infection.
Jasmine plant leaves turning red due to a fungal infection.

Powdery Mildew

This species of fungus will make the jasmine plant look like white polka dots all over the leaves and stems and slowly will also start turning them pale red. If not fixed the pant could die. If your jasmine plant is infected with powdery mildew, the main issues affect the buds, which will grow deformed as new growths or stems. You should prune the vegetation around the plant and move the plant towards a location where it can get more direct sunlight. It is super important not to over-water and/or over-fertilize the plant and apply protective fungicides high in sulfur or potassium bicarbonate. If the disease is well spread out, then use a fungicide containing myclobutanil or, if you prefer, organic ones such as neem oil, jojoba oil or horticultural oil which will eradicate the infection in a couple of weeks.

There you go! Now you have the clues and signs to look out for when your jasmine's leaves are turning red.

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Star jasmine red leaves
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