Are your oregano leaves yellow? Learn why & how to fix

Starting an oregano plant from seed holds a particular type of attraction for both experienced and new gardeners.

But why do leaves turn yellow, seemingly overnight, when everything is going so well?

Understanding yellow oregano leaves

Do not despair. Yellow leaves on oregano plants are, of course, a real problem that you need to address. But often, oregano plants will develop yellow leaves as a way of saying that you need to adjust how you care for your oregano plant.

Here in this article, we will look at the causes of yellow oregano leaves but also give you easy-to-follow action points if you have oregano plants where the leaves are turning yellow. 

But first, you must ensure that the leaves turning yellow are not a part of the plant’s natural growth and development.

When leaves turn yellow, but all is well.

Healthy oregano plants do not have yellow leaves. And this is true for both outdoor plants and oregano potted indoors.

And this is true except for the start and end of a plant’s natural life.

1. Yellow leaves at the beginning of a plants life

First leaves and true leaves on young parsley plant grown from seed
Parsley seedlings with first and true leaves

You plant oregano seeds and wait for the seeds to germinate and sprout cotyledons – or first leaves. These first leaves are generic looking and are simply there to help the plant grow and develop.

As the oregano seedling develops more leaves – so-called true leaves – we start to see the characteristic form and shape of the oregano plant we are growing.

And when the true leaves have developed, the first leaves no longer have a role to play. As they wither away, the leaves often go yellow and fall off.

This process of cotyledons turning yellow is, in other words, natural and a part of the plant’s natural growth.

Actually, when transplanting tomatoes, we plant the seedlings deeper than they grow as new roots develop from the stem. Here, we often have to remove the cotyledons or first leaves when planting the tomatoes deep.

2. Yellow leaves at the end of a plants life cycle

Oregano is a perennial herb that will come back year after year when looked after and allowed to grow properly. Still, there comes a time when the oregano stems have grown thick and woody, and the plant has given all the harvests it has to offer.

And when your plant is at the end of its lifespan, leaves will go yellow, and there is little to do to reverse the plant’s life cycle.

When oregano plants turn yellow as a cry for help

Oregano leaves can turn yellow for a variety of reasons. And often, it signals to us as gardeners that we must consider how we care for our plants.

1. Over-watering your oregano plants

Oregano is a Mediterranean herb and is, as such sensitive to over-watering. You need to be careful when watering oregano plants as excess water will lead to root rot and kill your plant.

Giving your oregano plant too much water is the most common cause of oregano leaves turning yellow. And watering plants too much and too often usually happens for one of the following three reasons:

1. Using the wrong pot or type of soil

Oregano needs a pot with drain holes and well-draining soil.

You can add perlite or coarse sand to your soil to improve drainage.

The key is that you need well-drained soil for your oregano plant to thrive and develop.

2. Loving your oregano plant to death by watering

New gardeners especially tend to overwater plants, even when remembering to check for soil moisture.

The fear of not watering enough can make even experienced gardeners overwater their plants. And when the plants turn yellow due to over-watering, it is easy to assume that you need to water more.

This scenario leads to roots sitting in constant wet soil and root rot.

Tip: Bottom watering your potted oregano plants is one of the easier techniques to learn how to adopt better watering habits. 

3. Using pots that are too big for the plant

As a rule, we should water herb plants thoroughly but not too often. And this is especially true for Mediterranean herb plants like oregano – but also thyme, rosemary, tarragon, lavender, and sage.

These Mediterranean herbs prefer a mild dry-out between waterings.

But when you have a herb plant growing in a pot that is too large, there is a risk that the roots will sit in wet soil at the bottom of the pot while the top half of the pot is dry.

And when you water again, the problem is magnified, and you risk damaged roots and root rot.

2. Yellow leaves due to insufficient light

Oregano plants like full sun and wants a minimum of 6 hours of direct sunlight to thrive. And if you do not give your oregano plant enough light, the leaves turn yellow.

Leggy seedlings and plants are other signs of not giving your plants enough light.

For potted oregano growing indoors, the rule of thumb is 12 hours of light and 8 hours of night rest.

For indoor plants you can see if lack of light is the reason for leaves turning yellow by simply inspecting the plant. If lack of light is the cause, you will notice that the yellowing is most noticeable on the side of the plant that is the farthest away from the light source.

3. Not enough nutrients or fertilizer

Oregano is one of those herbs that will grow in pretty much any soil as long as it drains well and is not too rich or fertile.

Still, oregano may suffer from yellow leaves if the soil is too depleted and lacks sufficient nutrients, especially nitrogen.

But as oregano is sensitive to overly fertilized soils, I recommend using half the recommended dosage of a balanced liquid plant food or organic fertilizer.

Remember that you can always add nutrients to your soil if needed – but it is much harder to take away when given.

How to prevent fertilizer burn

The best way to prevent fertilizer burn is simply diluting the fertilizer by giving half the recommended dosage.

But if you have been giving your plants too much fertilizer and leaves are turning yellow; you can flush the soil with water.

Water thoroughly and let the excess run off via the drain holes. Repeat the process two more times and then monitor and wait for the plant to react before repeating the process.

Seedlings do not need fertilizers in their early stages of development. As a rule of thumb, start using a fertilizer after first transplant when potting up the seedling to a larger pot. 

Pests and fungal diseases

Pests like aphids, spider mites, and fungal diseases like rust are examples of pests and diseases that can cause leaves to turn yellow [1].

We use our Neem oil mixture as our preferred natural pesticide, fungicide, and systemic insecticide.

And as always, with any pest or fungal disease, early detection is key to helping rescue an infected plant.

Summary:

If you are having problems with yellow leaves on oregano plants, I recommend you first consider your watering habits.

If this does not solve your problems, look at the plant’s access to sunlight and use of fertilizers and inspect the plant for possible pest and fungal disease infections.

And if you are still at a loss, I recommend re-potting the plant outdoors or in a new pot with new soil. 

[1] https://plantvillage.psu.edu/topics/oregano/infos

Meet the author: Mattias is an experienced gardener spending most of his free time on his knees among herbs, plants, and garden vegetables. For the past two years, he has been sharing gardening projects and how-to tutorials on the NordicLavender website and YouTube channel.