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

The process of starting an oregano plant from seed holds a special type of attraction for both experienced and new gardeners.

But why is it that leaves turn yellow, seemingly over night, when everything was going so well?

Understanding yellow oregano leaves

Do not despair. Yellow leaves on oregano plants is of course a real problem that needs to be addressed. But often, oregano plants develop yellow leaves as a way of saying that you need to make some adjustments to the way you are caring 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 need to make sure that the leaves turning yellow are not a part of the plants natural growth and development.

When leaves turn yellow and all is well

Oregano plants are not meant to have yellow leaves. This much we know. And this is true for both outdoor plants and potted oregano.

A healthy oregano plant should never have never have leaves that turn yellow. Right?

Well, it is true with the exception of the start and end of a plants 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 plants 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 give.

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

When oregano plants turn yellow as a cry for help

Oregano leaves can turn yellow for a variety of reasons. And often it is a signal to us as gardeners that we need to look at how we are caring 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 you water oregano plants as excess water will lead to root rot and inevitably kill your plant.

Giving your oregano plant too much water is by far 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 wrong pot or type of soil

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

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

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

2. Loving your oregano plant to death by watering

Especially new gardeners have a tendency to water plants too much even when remembering to check for soil moisture.

The fear of not giving enough water results in giving too much water. 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 a roots sat 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 the Mediterranean herb plants like oregano – but also thyme, rosemary, tarragon, lavender and sage.

These Mediterranean herbs actually prefer a mild dry out between being watered.

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 when 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 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 and 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 type of 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 and 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 a lot harder to take away when given.

How to prevent fertilizer burn

The best way to prevent fertilizer burn is to simply dilute 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 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 and spider mites as well as fungal diseases like rust are examples of pests and diseases that can cause leaves to turn yellow [1].

We use our own 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 help rescue an infested plant.

Summary:

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

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

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.