The reason sage leaves turn yellow is often a sign of stress because of damp soil. Sage is drought resistant and prefers soil to dry out between bouts of watering. Sage leaves can also turn yellow because of too much nitrogen due to fertilizer or a nitrogen deficit because the roots are pot bound.
Sage grows best in sandy, well draining soils when watered once every two weeks. The sage leaves grow best in terms of aroma and flavour when in low to medium nutrient soil rather then high nitrogen soils.
Keep reading to learn why your sage is turning yellow and how, with a few simple adjustments to the growing conditions you can solve the problem of yellow leaves…
Under Watering or Over Watering Causes Yellow Leaves
By far the most common reason for sage leaves turning yellow is as result of over watering.
Sage is a Mediterranean herb which prefers well draining soil, full sun and it can tolerate drought.
If the soil is constantly moist then sage leaves will turn yellow as a sign of stress as the roots prefer the soil to dry out somewhat between bouts of watering rather then persistent moisture.
Sage is more likely to wilt and suffer from fungal disease when in damp soils. (Read my article on why sage plants wilt and how to solve it).
There are four main reasons for persistent moisture around the roots of sage that cause the leaves to turn yellow:
- Over watering
- Slow draining soils (such as clay)
- High rainfall
- Pots without drainage holes in the base
In most climates sage should be watered around once every two weeks if the weather has been a mixture of overcast days, some sun and perhaps some rain.
In hot weather water sage every week. If there has been rainfall and the moist feel moist then skip watering until the soil has become somewhat dry.
If you are watering sage more frequently then once per week you are likely over watering the plant and the leaves can turn yellow.
The solution for over watering…
Scale back the watering so that the soil has a chance to dry out between rainfall or additional watering as sage is native to dry Mediterranean conditions so can be susceptible to over watering by gardeners.
Water sage with a generous soak each time you water to encourage the roots to establish.
Scale back the watering and allow the soil to dry out and the sage leaves should begin to recover after 2 weeks. Sage plants that are watered appropriately have a better flavour.
Slow Draining Soil…
Another important issue to address is soil drainage.
Sage grows in sandy or stony soils on hillsides in Southern Europe, therefore they are adapted to soils which do not retain much moisture.
Slow draining soils such as clay or rich compost in boggy areas of the garden are contrary to the sage’s preferred soil conditions and retain too much moisture around the roots of the sage which can cause stress and turn leaves yellow.
The solution for slow draining soils…
Sage grows very well in pots due to their favourable drainage and it is very easy to control the soil profile. If your garden has slow draining soil then planting in pots is a great option to keep the plant healthy and the leaves green.
You can also amend the planting area (if your planting in garden boarders) or the potting mix with horticultural sand or grit.
The sand or grit will help to replicate the sandy soil conditions that sage is adapted to and improve the drainage which helps to keep the roots dry and stops the leaves turning yellow.
Mix at least 20% sand or grit with multipurpose compost when planting your sage plant in the garden soil or in a pot for the optimal drainage so that the roots are able to dry out after watering.
High rainfall is also problematic for sage and Mediterranean herbs in general, however sage is a resilient plant and can adapt to rainy climates as long as it is in full sun and the soil has been amended before planting to improve the drainage.
The solution for high rainfall…
With persistently rainy climates I would recommend that you amend the soil with at least 30% sand or grit (by volume) with the rest compost. Sage grows in its native range on hillsides in soil that is very sandy so do not be afraid to add lots of sand or grit as too much sand is always better then not enough.
With improved soil drainage sage can grow very well in climates with high rainfall with the leaves can grow a healthy green rather then yellow.
Another common mistake is to plant sage in decorative pots without drainage holes in the base or use a drip tray to catch excess water out the bottom of the pot.
If water cannot drain away then the soil quickly becomes damp and the sage will start to show the signs of stress from too much water with leaves turning yellow and a wilting appearance.
Choose a pot that is 12-16 inches across with drainage holes in the base and this will allow the water to escape and prevent sage leaves turning yellow.
If your sage plant is wilting and leaves are turning brown then it is likely the sage plant is suffering from root rot. Read my article for why sage plants turns brown and how to solve the problem.
Under watering sage is not a common problem as it is drought resistant thanks to its Mediterranean origin. However if the pot of sage is indoors and has been neglect for weeks then sage leaves can turn yellow as a result.
Water indoor sage plants once every two weeks during the Spring, Summer and Fall and the sage should recover if the leaves are starting to look yellow.
Another potential problem is if the pot for the sage plant is too small and made from plastic or metal. Small pots heat up quicker in the sun which causes the soil to dry out too quickly for the roots to uptake.
A larger pot has more soil to give the roots a chance to establish so it can draw up the water it requires. Choose a clay, terracotta or ceramic pot as they do not heat up as quickly as thin plastic or metal pots which can contribute to the soil drying too quickly.
Too Much Fertilizer, Nutrient deficient or Pot Bound Roots
Sage is a Mediterranean herb that grows in sandy soils on hill sides in southern Europe.
Therefore many of varieties of sage are adapted to soils that are low to medium, in terms of nutrients with a good proportion of sand or grit which are well draining.
If sage is planted in soil with a high nitrogen content (such as soil amended with manure) or the use of excessive fertilizer then this is contrary to the sage’s preferred soil conditions which can cause stress such as:
- Leaves turning yellow
- A drooping appearance of the foliage and stems
- Less aroma from the leaves and less flavour
Nitrogen fertilizer can be useful for stimulating growth in sage plants in certain conditions.
However sage is not a fussy plant and often does not require any additional fertilizer. In fact, if you are growing sage for culinary purposes, too much fertilizer is to the detriment of the flavour of the herbs, not to mention causing the yellow appearance.
If you have applied fertilizer to a sage plant and have seen an excess amount of growth with yellowing leaves then refrain from using more fertilizer for a while and the sage should recover.
Sage plants are low maintenance and the more you can replicate the their natural growing conditions the better they should grow and the stronger the taste of the leaves.
To recreate the low to medium fertility soil conditions in which sage thrive, mix at least 20% horticultural sand or grit with multipurpose compost into the planting area or the pot.
This ensures that sage has the right balance of nutrients and good drainage so the plant is healthy and the leaves are a healthier green rather then yellow.
Not Enough Nitrogen
Whilst sage prefers low to medium nutrient soil, it does require some nitrogen, phosphorous and potassium (as well as some trace minerals) to grow healthily.
A deficit of nitrogen will result in leaves turning yellow, which may seem confusing as too much nitrogen also cause leaves to turn yellow.
However sage rarely suffers from a nitrogen deficit and the reasons for sage turning yellow is usually as a result of over watering or too much fertilizer rather then not enough nutrients, but there are some scenarios where this can be an issue.
Sage leaves turning yellow because of a lack of nutrients tends to occur more when:
- Sage that is planted in a pot and has not been re-potted for many years
- A pot that is too small and the plant has become root bound
In both these cases the sage plant can exhaust the nutrients of the pot due to the roots limited access to soil and nutrients.
The key to keeping sage healthy is to plant it in a pot that is roughly 12-16 inches across. This will help prevent the sage roots becoming pot bound so that there is more soil and therefore more nutrients not to mention insulation for the roots which are vulnerable to the cold.
Re-pot the sage plant if it looks yellow to a larger pot with new compost to provide the sage roots with more nutrients.
In this case a half strength general all purpose fertilizer (applied in the Spring) can be useful in terms of stimulating new growth and ensuring the sage has access to a wide range of nutrients in case it has been suffering from a nutrient deficit such as nitrogen or perhaps a trace mineral.
Applying fertilizer late in the growing season will stimulate growth that is more susceptible to frost damage so it is only apply fertilizer to sage once in the spring at half strength as too much will do far more harm then good.
This will stimulate growth and address the nitrogen deficit which will turn the leaves from yellow to green within a few weeks.
- Over watering is the most common reason for sage to turn yellow. Sage is a Mediterranean herb that prefers dry soil and does not tolerate damp soil which causes the leaves to turn yellow.
- Scale back the watering to once every two weeks, amend the soil with sand or grit and plant sage in pots to replicate the dry conditions of their native Mediterranean habitat.
- Too much fertilizer can be too harsh for sage and the excess nitrogen cause the leaves to turn yellow. Sage that has pot bound roots can suffer with a nutrient deficit and turn yellow. Apply a half strength all purpose fertilizer in the Spring and re-pot the sage if it is in a small pot with pot bound roots.