Marigolds (Tagetes spp.) are among the most popular starter plants out there. They are easy to grow, forgiving of some neglect, and generally low-maintenance.
But that doesn’t mean that growing marigolds are completely free of problems. One of the most baffling is when the leaves change color.
Here are some of the most common reasons your marigolds might change color and what to do about it.
Reasons Why Marigold Leaves Turn Colors
You can wind up with discolored leaves for several reasons, but they generally fit into three categories, including:
Unfortunately, some diseases are incurable, but most other reasons are easily fixed.
Age
Perhaps the most overlooked cause of leaf yellowing is simply aging.
As leaves get old, they will naturally yellow, whither, and fall off.
You can simply tell if age is the cause by checking the juvenile leaves.
If they’re normal and healthy, you know it’s just age, but if the juvenile leaves are also turning yellow, there’s an actual problem.
Disease
Diseases can be transmitted through contaminated soil, insect pests, and cross-contamination from unsterilized tools.
Aster Yellows
Aster yellows is a bacterial disease transmitted by leafhoppers that causes yellowed leaves and leads to stunted, deformed blooms.
As this is a bacterial infection, there’s no cure, and any plant should be immediately removed and burned.
Crown Gall
This nasty bacterial disease enters damaged marigold roots and causes galls at or below ground level.
The galls make it difficult or even impossible for nutrients and water to pass from the roots to the upper portions of the plant.
As a result, the plant may suffer from yellowing leaves, wilting, or stunted growth.
This is an incurable disease, so any infected plants must be destroyed.
Sterilizing the soil can help prevent further spread.
Powdery Mildew
Most often caused as a side effect of infestations, powdery mildew is well-known for the talc-like powder that forms on infected leaves.
This fungal infection is generally relatively mild, but if left untreated, the mildew can cover so much of the leaf surface that it prevents photosynthesis.
This, in turn, leads to yellowing and may cause the leaves to become deformed.
Thankfully, powdery mildew is easy to control if you use a neem foliar spray.
The neem will not only kill the fungus, but it will also kill the pests that create honeydew (the substance powdery mildew is attracted to) on contact.
Root Rot
Root rot is a dreaded disease that both fungi and bacteria can cause.
This disease causes the roots to rot away, making it impossible for plants to absorb water and nutrients.
Most often, root rot will cause older, lower leaves on plants to turn yellow first.
Early treating root rot can save your plant and involves doing the following:
- Uprooting the plant.
- Removing any damaged roots.
- Sterilizing the roots.
- Replanting in sterile soil.
Neem soil soaks can help prevent root rot, but the best way to prevent it is to use proper watering techniques.
Verticillium Wilt
This fungal disease clogs the vascular tubes of infected plants, which can cause wilting and yellowed leaves.
As the disease progresses, the yellowing extends from the tips and margins, eventually turning brown and dying.
This is one of the few fungal diseases that cannot be cured, and you’ll need to destroy any infected plants.
Sterilizing the soil and practicing proper water techniques are the best preventatives.
Improper Watering
This is the single most common cause of plant problems out there.
Underwatering a plant is easily fixed, but too much water can lead to all sorts of complications.
Overwatering can lead to fungal and bacterial infections, increased risk of infestations, and even directly result in edema (water blisters).
Thankfully, avoiding overwatering is quite easy using the soak and dry method.
This simple method lets you know when to water and when to stop.
For marigolds, it’s time to water when the top ½” inch of soil is dry.
The trick is to add water slowly so that the soil is absorbing it as fast as your pour.
Pour the water slowly and evenly, working your way around the plant.
Try not to get the foliage wet, as this can invite problems if the leaves don’t dry quickly enough.
You’ll know it’s time to stop if the soil can no longer absorb as fast as you pour.
You can also tell it’s time to stop with potted marigolds when you begin to see moisture seeping from the drainage holes.
Nutrient Deficiency
Everyone knows that fertilizer contains nitrogen, phosphorus, and potassium (the NPK ratio), but plants need much more than that to stay healthy.
Some other important nutrients include micronutrients such as copper, iron, magnesium, and manganese.
When a plant doesn’t get enough of these nutrients, it can lead to several conditions, including yellowing leaves.
You only need a small amount of these nutrients, and too much can result in leaf burn or other consequences.
Aim for a balanced fertilizer with added micronutrients for the best results.
Poor Lighting
Marigolds love sunlight and need at least 6 hours of direct light daily.
Anything less than this can lead to a condition called chlorosis, where the leaves cannot produce enough chlorophyll, making it harder to photosynthesize.
To prevent this, make sure your marigolds are always in a sunny location, even if the direct light is in the morning or evening.
Temperature
When temperatures go outside the marigolds’ comfort zone, they can suffer or be fooled into thinking winter’s approaching.
Additionally, indoor plants are used to steady temperatures, so sudden fluctuations such as drafts from an AC or vent can cause the plant distress, which will also result in yellowing leaves.
There’s not a lot you can do for marigolds planted in the ground when there’s a sudden cold front, but for potted plants, you can simply move them indoors or change their location to stabilize the situation.
