Herb leaves turn yellow because of overwatering or underwatering which prevents the herbs roots transporting nutrients and water properly to the leaves which causes them to turn yellow and drop off. Herbs with root rot turn yellow with a drooping appearance.
|Causes:||Reasons for Herbs Turning Yellow:|
|Root rot caused by overwatering, boggy soil and pots without drainage.||Root rot damages the roots of your herb and prevents it from drawing up nutrients and moisture causing yellow, drooping leaves.|
|Drought stress because of underwatering, small pots, and poor soil.||Drought stress causes annual herbs such as basil and cilantro to wilt and turn yellow when the soil is too dry.|
|Lack of sun.||Mediterranean herbs require full sun (6 hours or more) whereas annual herbs require partial sun. Too much shade causes leggy growth and yellow leaves.|
|Nutrient poor soil.||Poor soil caused by a low soil pH or because of nutrient deficiency causes herbs to turn yellow.|
Keep reading to learn why your herbs are yellow and how to implement the solutions to save your yellowing herbs…
Herbs Turning Yellow due to Root Rot and Fungal Disease
- Symptoms. Leaves and possibly stems are turning or brown with drooping appearance.
- Causes. Watering too often, slow draining soils or pots without drainage holes in the base.
The most common reason for herbs turning yellow is because of too much moisture around the roots which promotes the conditions for root rot and fungal diseases. Root rot is causes by overwatering, slow draining soils and pots without drainage holes in the base and causes the leaves to turn yellow and droop.
All herbs require well draining, porous soil with a light, friable structure that allows water to infiltrate effectively.
If the soil becomes saturated then herb’s roots can develop root rot and they can no longer respire which prevents them from up taking the nutrients and moisture they need causing the leaves to turn yellow as a sign of stress.
All herbs suffer when there is too much moisture around the roots but Mediterranean herbs in particular (lavender, rosemary, sage, thyme and oregano) are adapted to growing in dry sandy soils which drain very quickly and hold less moisture which leaves them more vulnerable to root rot.
For Mediterranean herbs it is important to amend the soil with sand or grit to emulate the sandy Mediterranean soil conditions and ideally plant them in pots (with drainage holes in the base) for more favorable drainage and water them less often.
(Read my article, how often to water herbs).
Avoid planting herbs in clay soils or boggy areas as they retain too much moisture and your herbs are likely to turn yellow and die back.
How to Save Yellow Herbs with Root Rot
- Scale back the watering. Mediterranean herbs typically require watering once every 2 weeks when in pots and do not require any water at all once established in garden boarders. If you are watering more frequently then this, you are overwatering your Mediterranean herbs and this is the most likely cause of your leaves turning yellow.
- Annual leafy herbs such as basil, cilantro, dill, mint, chives and parsley require consistently moist soil so should be watered more often then Mediterranean herbs but the soil should be evenly moist rather then saturated or boggy.
- Improve the soil drainage. Mediterranean herbs should be planted in soil that is approximately 70% compost to 30% sand or grit to replicate the well draining gritty soil conditions of their native Mediterranean environment. Creating the right soil mix for Mediterranean herbs is critical to avoid root rot and yellow leaves so watch my video on how to create the optimal potting mix for lavender: (please note that the same soil mix applies for all Mediterranean herbs).
- Transplant your herb into a different pot with drainage holes in the base. Herbs should always be planted in pots and containers with drainage holes to allow excess water to escape after watering to prevent the soil becoming saturated. Be careful of saucers and trays underneath your potted herbs as these can keep the soil at the bottom of the pot damp and prevent water draining away from the roots effectively.
- When you are transplanting your herbs inspect the roots. Trim of any roots that are dark, feel mushy, rotten or have a bad smell. Roots should be lighter in color (they can look brown and woody on some herbs) and feel firm without any significant smell. Trim any diseased looking roots back to healthy growth with a sterile pair of pruners. Wipe the blades of the pruners with a cloth soaked in disinfectant to prevent spreading any fungal pathogens to otherwise healthy roots.
- Replace the soil. Discard the old potting soil as it can host the fungal pathogens that are responsible for root rot so it could potentially reinfect the plant. Replant leafy annual herbs (such as basil and cilantro) in good compost and Mediterranean herbs in compost amended with sand or grit.
- Cut back any yellow leaves. Any yellow leaves are not likely to recover if overwatering is the cause so cut them back to the base of the plant with sterile pruners.
If most of the herbs leaves are yellow or the roots are mostly rotten then the herbs is likely to die so discard it and replant new herbs in different pots.
Preventing root rot is always better then trying to solve it so the best option may be to replace the herbs and adhere to the best practices of watering (once every 2 weeks for Mediterranean herbs), planting herbs in the appropriate soil (amended with sand or grit for Mediterranean herbs) and planting your herbs in pots with drainage holes to prevent root rot and yellow leaves.
(Read my articles on the best pots for herbs, the best soil for herbs and and how to revive dying herbs for more information on preventing root rot).
Underwatering Causes Herbs to Turn Yellow
- Symptoms. The symptoms of drought stressed herbs are similar to overwatered herbs (somewhat confusingly) with yellow leaves and a wilted appearance.
- Causes. Underwatering, small pots, soil that drains too quickly.
To distinguish whether your herbs are turning yellow from underwatering or too much water, drought stress is the cause if…
- The herbs leaves are turning yellow form the bottom of the plant.
- The leaves appear wilted and can curl inwards.
- The soil feels dry and baked rather then boggy.
Mediterranean herbs are drought resistant as they have adapted to the hot and dry Mediterranean climate and actually thrive in well draining soils so most the the time it is overwatering causing their yellow leaves rather then underwatering although this can happen in pots that are too small.
Leafy annual herbs (such as basil, cilantro, parsley, mint and chives on the other hand are more likely to suffer drought stress which causes the leaves to turn yellow with a wilted appearance.
The leafy annual herbs require the soil to be moist (yet well draining) which is achieved by planting them in compost as compost can retain moisture, yet has a porous structure that allows excess water to drain away from the roots which is the perfect balance for annual herbs.
Of course the right frequency of watering is also very important for preventing drought stress and ensuring every time it is a thorough watering rather then a light watering, so the moisture reaches the roots where it is required.
Smaller pots also dry out much quicker particularly if your herbs are in full sun which can be responsible for your leaves turning yellow.
How to Save Yellowing Herbs Because of Drought Stress
- Give your herbs a through watering so that excess water trickles from the base of the pot. Whether your herbs are planted in raised beds, garden boarders or in pots they all require a generous soak to ensure the water reaches the roots. Light watering causes the roots to grow near the surface of the soil which increases the herbs vulnerability to drought.
- Water leafy annual herbs so that the soil is consistently moist. How often to water your herbs depending on many variables such as climate, weather and soil so the best advice to ensure that the compost feels moist to a fingers depth in the soil. When the soil is starting to feel as though it is beginning to dry out give your herbs a good soak. Typically this means watering every 3-7 days depending on the time of year but watering leafy annual herbs nearly every day can be required at the hottest times of year.
- Always plant your herbs in a larger pot of around 12 inches across if possible. Herbs can grow perfectly well in small pots but it should be noted smaller pots dry out much quicker in the sun as they have less capacity for soil and therefore less capacity for moisture. Larger pots have more soil and therefore hold more moisture for the herbs roots to uptake water and nutrients as required.
- Plant your annual herbs in good compost if your soil is sandy. Leafy annual herbs require good compost to avoid drought stress and yellow leaves. If your soil is sandy or stony, it is likely to drain too quickly for leafy herbs and therefore it is better to grow your herbs in pots with good compost or significantly amend your soil with lots of organic matter (leaf mold and compost are the best materials for retaining moisture) to create the optimal balance of moisture for your herbs and prevent yellow leaves from droughts stress.
Reviving herbs turning yellow from drought stress is a lot easier then form overwatering and often the herbs can make a good recovery if you create the optimal conditions and increase the watering.
Lack of Sun Turns Herb Leaves Yellow
- Symptoms. Poor stunted or very slow growth. Stems can grow leggy as they herb grows to the strongest source of light. Leaves turn yellow usually from the bottom of the herb.
- Causes. Mediterranean herbs require full sun (6 hours or more) and turn leggy and yellow in the shade. Leafy annual herbs (such as basil and cilantro) can grow in partial shade but turn yellow in full shade.
Mediterranean herbs thrive in full sun in their native range in Southern Europe, so locate them in the sunniest area of your garden or they grow leggy, turn yellow and die.
Trim back any leggy growth by about one third to stimulate new growth and for your herbs to recover.
Leafy green annual herbs such as basil prefer morning sun followed by afternoon shade. This allows them to grow tho their best in the sun yet protects the herbs from drying out as temperature peak in the midday and afternoon.
If your leafy annual herbs are in too much shade, move them to an area of more sun and trim back any drooping affected growth which stimulates healthy green leaves to grow which have a much better culinary value.
Nutrient Poor Soil Can Causes Herb Leaves to Yellow
- Symptoms. Poor stunted growth, with leaves yellow and brown.
- Causes. Sandy soil or smell pots that have limited soil and therefore limited nutrient availability.
Mediterranean herbs are native to Southern Europe where they grow in sandy, gritty soils that are medium to low in nutrients.
Therefore herbs such as lavender an rosemary actually thrive in nutrient poor soil, so the reason they are turning yellow is more likely due to overwatering or damp soils.
However Mediterranean herbs typically prefer a soil pH of 6.5-7.5 so if your soil is particularly acidic then this can prevent the roots uptaking certain nutrients in the soil which can cause foliage to turn yellow.
If your garden soil is very acidic (lower then pH 6.5) then always grow herbs in pots instead. Commercially available compost and potting soil is within the appropriate pH range to grow herbs unless it is ‘ericaceous’ compost, which means that it is formulated for plants that prefer acidic soil conditions.
Leafy annual herbs such as basil and cilantro grow best in compost or in a vegetable garden amended with organic matter (which contains more nutrients) rather then sandy soil which can cause the leaves to turn yellow due to a lower concentration of soil nutrients.
Annual herbs planted in a relatively small pot may also be suffering a nutrient deficiency as there is less soil and therefore less nutrients available for the roots, which causes the leaves to turn yellow.
The solution is to replant your herbs in a larger pot with new compost and they herbs should recover and start growing again.
Cut back any yellowing foliage to stimulate new growth which should be healthy and green.
Can You Eat Yellow Herb Leaves?
Do not eat the yellow leaves of herbs as they are not likely to taste very good and contain a much lower concentration of the essentials oils which give herbs their aroma and flavor. Instead prune back your annual herbs to around 8 inches tall to stimulate new growth of healthy green leaves with a much better flavor.
- Herb leaves turn yellow because of root rot caused by overwatering. Overwatering herbs prevents root respiration, which interferes with the roots ability to draw up moisture and nutrients from the soil causing the leaves to turn yellow and droop as a sign of stress.
- Herb leaves turn yellow because of dry soil. Annual herbs such as basil and cilantro require moist, porous soil and frequent watering in hot weather to prevent leaves turn yellow and wilting. Small pots dry quickly in the sun causing herbs to turn yellow as a sign of stress.
- Mediterranean herbs require 6 or more hours of sun, whereas annual herbs require partial sun and turn yellow with poor growth in too much shade. Move your herbs to a sunnier location and cut back any yellow growth to stimulate healthy green leaves.
- If your soil is sandy or gritty or your pots are very small then annual herbs such as basil and cilantro can turn yellow because of a lack of nutrients. Repot your herbs to a larger pot with good compost and cut back yellow leaves and the herbs should recover.