The rosemary is a drought-resistant species that flourishes on arid soils that drain well and full sun. So the reason that rosemary leaves turn yellow is due to excessive nitrogen levels in the soil, or as an indication of stress because of damp soils that result from of excessive watering and slow drainage soils.
The leaves of rosemary potted plants may also turn yellow when the pot isn’t big enough or the roots is pot bound.
The rosemary plant is found throughout the Mediterranean region of Europe in soils that vary from acidic to alkaline, with a pH between 6 and 7.5 Therefore, the alkaline soils that cause chlorosis is unlikely to be the reason for the leaves of rosemary turning yellow, which tends to occur for plants that can only tolerate neutral or acidic soils like roses.
Continue reading to find out the reason the leaves of your rosemary have turned yellow and the best way to fix the issue…
High Fertile Soil Causing Rosemary Leaves to Turn Yellow
One of the most common causes that rosemary leaves change color is that they are grown in soil , which may be amended by manure (which is rich in nitrogen) or due to excessive use of fertilizer.
The rosemary plant is native in their native Mediterranean area of Europe which is where they flourish in nutrient-poor soils, such as sandy or stony.
Rosemary is specifically designed to the soil type of this area and it is in these conditions, that rosemary has the strongest aromas and most flavorful leaves that can be used for cooking.
Thus, more issues that cause yellowing of the leaves could result from excessive nitrogen, not the result of a deficit.
The rosemary plant is adaptable that can thrive in a variety of soil types , provided that they drain well (loam and chalky, sandy or soils) however when the soil is high in nitrogen or if you’ve used a heavy nitrogen fertilizer, then the leaves of rosemary can change color as a result of stress.
Other indicators of stress in nitrogen include:
- A less pronounced aroma and flavor of the leaves
- A greater amount of foliage with less flowers
In actual research shows that rosemary grown with more stone, sand or perlite that had lower levels of fertilizer created higher levels of oils within the leaves (then the ones planted in more fertile soils with higher fertilizers) which enhances the flavor and smell that the herb.
The most important thing to ensure that your rosemary is healthy is to mimic the conditions of natural growth in your garden , to which they have been adapted.
This is because they should be planted in a sandy soil mix that does not hold as much or water or hold as many nutrients (around 20 percent sand or grit, to 80percent compost or potting soil) will help recreate their natural soil type and permit adequate drainage while creating a low to medium nutrients environment where rosemary thrives.
If you’ve established Rosemary in a sufficient pot (smaller pots are less able for soil, and consequently the roots are less accessible to nutrients) It will get every nutrient it needs without the need for fertilizer.
(Read my article on selecting the most suitable containers for the rosemary).
A balanced, fertilizer that is weak that is applied every year in spring is all that a rose will require, but it’s unlikely to be required in the same way that it is for plants that are growing like Roses or Hostas that are heavy feeders and require regular feeding.
Other Possible Causes
Yellow Leaves Due to Lack of Sun
Rosemary is an herb that thrives in the blazing sun (in the South of Europe) for all of the year, with some overcast days and mild winters.
If your Rosemary isn’t in full sunlight, it may grow in a sluggish and possibly leggy with less flowers. The leaves may be yellow, a sign of poor plant health.
It is, of course, simple to correct, simply either shifting the potted rosemary to an area that receives full sunshine or transferring the rosemary into a more sun-filled area if it’s placed in soil that is not fertile.
In a couple of weeks, the plant will begin to grow stronger, with more growth, a stronger scent and possibly more flowers and the leaves changing from yellow to healthier green.
Pot Bound Rosemary Plant
The size of the pot is crucial in the growth of healthy rosemary. If the pot isn’t big enough, it means that the rosemary roots be in little space to get the nutrients and water they require, that can cause the leaves to turn to yellow.
Place rosemary in a pot approximately 12-16 inches wide (or greater) to make sure the pot is large enough for soil , so that the roots can grow properly without becoming unnaturally pot bound and unhealthy.
If the pot isn’t big enough then the soil will dry out quickly in the sun, before the roots get an opportunity to absorb the water too fast even for rosemary, which likes soil that is dyed.
The soil also acts as an insulation to protect the roots to protect them from cold. Rosemary isn’t particularly cold-hardy and could require protection during winter. The roots are the most susceptible to cold temperatures, so the pots are small and would not have enough soil to protect the roots from the frigid winter temperatures.
Soil pH and yellow leaves of rosemary (Alkaline soils aren’t the reason)
For many plants that thrive in soils with acidity (roses and azaleas, rhododendrons, and so on.) the reason that their foliage turns yellow due to of chlorosis, which is caused by soil that is too acidic and the plant is unable to absorb the nutrients it needs.
In these situations, the leaves turn yellow , but the veins on the leaves remain green.
It’s not the case with Rosemary! !
I have seen gardeners leap into the conclusion that the soil is too acidic or deficient in iron, and they then apply iron chelates and alter the soil to ensure it becomes more acidic.
The roses are naturally found in calcareous soils of the Mediterranean countries. It is suited to thrive on alkaline soils (as as well as moderately acidic soils) consequently the leaves will not become yellow due to chlorosis since rosemary is tolerant of an pH range between 4.5 to 8.3 however the ideal range for the growth of healthful rosemary is pH 6. (mildly acidic) to pH 7.5 (slightly alkaline).
The majority of garden soils are around pH 6-7, which is the pH of the majority of organic matter after it has been completely decomposed. So soil pH is likely to cause the leaves of your rosemary to turn yellow unless your soil is extremely acidic or alkaline, in which the case, there are very few healthy plants that will thrive in your garden. It is more likely the leaves turn yellow because of water stress or excessive nitrogen.
Over Watering, Humidity or Slow Draining Soils
The rosemary is a drought-resistant plant that once established, is susceptible to suffering when it is watered excessively often, in areas with high humidity, or when the roots are located in slow draining soils, all of which could contribute to the leaves becoming to yellow…
One of the main reasons why Rosemary plants turning yellow is due to excessive watering.
The rosemary plant is found in the Mediterranean region of Europe which is well-adapted to sun-filled, well-drained and often stony or sandy soils that receive little or no rainfall.
The thin, needle-like the leaves of rosemary have been designed in a manner that keeps the transpiration (water loss) of the leaves to the minimal.
The rose is suitable for dry soils in desert climates. Therefore, when it is planted by gardeners, it is usually over-watered. The leaves may change color as a result of stress.
Rosemary likes to dry the soil all around its roots in between every watering session.
If the compost or soil in a pot remains damp, then it is in opposition to their preference for dry conditions. The leaves may change color, turning yellow or even brown.
Slow Draining Soils
It could be that the rosemary is not regularly maintained and the leaves remain yellow due to the soil being slowly draining, or is boggy, which can cause the same effect as excessive watering.
The native rosemary that is grown in France typically grows in sandy soils or on hillsides in which the soil drains rapidly and doesn’t hold on to the moisture effectively.
If you have rosemary in:
- The soil is compacted or heavy clay.
- A very rich compost that holds plenty of moisture, without grit or sand
- Garden areas which tend to be boggy, like low-lying areas or close to streams or a spring.
- A humid microclimate in your backyard without breeze (such as in the corner of the patio)
…then then Rosemary may suffer from sensitive to water that makes its leaves yellow.
Another issue is if your Rosemary is planted in a container or pot that doesn’t have drainage holes at the base, meaning that the excess water doesn’t go away and the soil remains damp, which can lead to the leaves turning yellow and root rot.
(Read my article on the the best soil to plant rosemary in pots).
A humid climate is another issue that could cause rosemary leaves to turn yellow due to stress from moisture.
The natural growth of rosemary is evident in the coasts in Southern Europe where there is an ongoing breeze that flows through the leaves. If the air is not dry and possibly humid, the rosemary leaves can change color from brown to yellow in a sign of stress.
It is also a possibility for fungal and root rot. Rosemary likes open spaces with a breeze on occasion and if the plant is buried in the area of a patio, or in a more humid microclimate, in addition to other plants, it could be affected by.
How to Resolve Yellow Rosemary due to Water Sensitivity
The most effective method to treat Rosemary that has turned yellow due to excessive moisture is to:
- Reduce water intake to at least once every two weeks
- If the soil drains slowly, modify the soil by adding sand or grit
- Transfer the Rosemary into an area that has adequate drainage
- Transfer the rosemary that has been planted in pots, to an open space in your garden to allow for better airflow
Once Rosemary is planted in a specific area of your garden, it’s drought-resistant (thanks due to the Mediterranean roots) and only requires regular watering every two weeks with a good soak.
Always soak your Rosemary with a good soak because this helps the roots to grow correctly and increases the plant’s resistance to dry conditions.
Dry the rosemary for two weeks, and then regularly water it every two weeks throughout the Spring until end of the Fall. If excessive watering is the issue, the leaves and roots should be able to recover and become healthier green instead of yellow.
If your soil is slow draining, I suggest amending the soil by adding the horticultural sand or grit. This will improve the draining capacity of soil, so that the roots don’t remain in a soil that is constantly damp.
For rosemary in pots, I suggest that you plantit in the soil mix of approximately 20% sand or grit to about 80 percent compost, as this mimics the soil conditions in the Mediterranean where rosemary flourishes.
If your rosemary is growing in clay soil that is heavy or in a boggy area, it is recommended to transplant the rosemary into a dry region and then amend your soil using grit or sand for better drainage, or maybe move the rosemary to pots.
Here’s a useful YouTube video on how to remove the rosemary plants and then transplant them while reducing any shock from transplants:
Containers and pots are another excellent way to increase air circulation around the plant since pots have better drainage conditions, allowing air to circulate more effectively around the rosemary contrasted with planting in garden soil.
(For additional reasons to have the dying of a rose and solutions, check out my post Why is my rose declining?)
- The leaves of roses may turn yellow due to nitrogen-rich soils or water sensitivity. It could also be due to being in a pot, or possibly the absence of sunlight.
- Rosemary can live in soil that is alkaline, so the reason for leaves turning yellow is not likely to be the result of chlorosis.
- Create the preferred Mediterranean conditions, which include full sun and well-drained soil. frequent watering, and low to moderate nutrients. The leaves that were yellow should come back and become green.