Black sage leaves are often caused by too much or little moisture, slow-draining soil, dry air or too much humidity, excessive rainfall, too much direct sun exposure, or excessive fertilization.
Identifying the causes of black leaves is one step away from saving your sage leaves and the plant from dying.
Black leaves or black tips is a gradual process that first develops with yellow or brown leaves.
Black leaves cannot be reversed and they will eventually droop and fall off. Just be sure to remedy the issue that caused the blackening of the leaves so other leaves don’t suffer the same fate.
In addition to simply cutting off the black leaves you want to give sage:
- well-draining soils
- containers with drainage holes
- sufficient watering
- adequate lighting
- optimum humidity
- and adequate fertilizing
Factors That Cause Black Sage Leaves and Remedy
Soil Factors
Poor Draining Soils
Soils that drain well will establish healthy roots since they have small pore spaces that will hold oxygen.
This allows the roots of the plant to easily absorb the oxygen for plant metabolic processes.
Slow draining soils will keep water around the roots and if this stays in place long enough, the water will displace the oxygen in those soil pores and suffocate the roots.
It will also support fungi that can contribute to root and stem rot which will further affect root performance and lead to death of the roots quite rapidly.
Dying roots will lead to black leaves and will kill the plant if action is not taken. It can also exhibit wilting as a sign the plant is in distress.
Therefore, if you see sage leaves turning black, begin to consider the type of soil the sage plant is established in and if it holds onto water or drains well. This herb performs best in a loose soil with some grit added for drainage.
Poor Draining Soil Management
If you don’t have perfect soil, there are a few tactics you can use to improve it:
- An important practice is adding organic matter like compost or well-rotted manure to your garden or container. Compost improves soil aggregation, which adds air pockets, filling them with oxygen. You can further aerate compost with perlite, mulch, vermiculite, peat moss, and sand.
- Another strategy is minimizing compaction (compressing soil pores), which removes air and hinders oxygen and water from moving into the soil. Compaction can cause soil baking as well, as there will be no moisture or air to insulate the soil and keep it at proper temperature.
Over time, soil in the container can have compaction due to watering and lack of water movement, as well as the breakdown of the aerated soil structure.
Gardeners can reduce compaction in the garden by not driving, walking on, or working on wet soil. For the potted sage, consider removing and replacing the old soil and then refilling the pot with a well-drained potting mix with perlite, mulch, vermiculite, or moss, or repotting the sage.
Planters can address drainage by raising the soil on a mound. This would mean putting in a drainage system to remove water- either digging earth channels and drains, or installing pipes at an angle to remove excess water from the garden.
You can also use:
- elevating containers
- using raised beds
- or choosing pots with drainage holes can improve soil drainage in container gardening
Water Factors
High Rainfall
Though sage thrives in a semi-arid climate, it can also be successful in rainy climates.
That said, high rainfall climates very much contribute to more favorable conditions for root rot, causing sage leaves to be brown and black.
By using well-draining soils, hilly areas of the garden, and proper drainage cups, this can be mitigated.
Improper Watering
Plants contain around 80 and 95% water and require it for photosynthesis, for the transfer of minerals and nutrients, and for proper foliage health, etc.
So properly water-balanced plants will be healthier, stronger, and resistant against infection and disease.
Improper watering will cause your sage leaves to turn black. It can either happen from overwatering or underwatering the plant.
Underwatering
If the soil is dry and crusty, it is indicative that the soil is under-watered. Underwatering denotes dehydrated soil for an extended period of time.
Sage is a drought-resistant plant and can thrive in very harsh dry environments but underwatering can also compromise the health of the plant.
An overwatered sage plant will push water through the edge of the leaves causing the veins at the edges to rupture thus browning and blackening the edges.
Overwatering
To determine if your Sage plant is getting too much water, look for signs of overwatering. These signs include soggy soil, soft, dark brown, rotten roots that feel slimy, mushy stem base that is in the soil, or an odor coming from the soil.
Overwatering sage plants routinely saturate the roots, leading to root rot.
When the plant has root and/or stem rot, roots are unable to supply water and nutrients, which leads to sage suffering from a sufficiency of water and nutrients, displayed as yellow, brown, or black leaves.
Tips for Correct Watering
If your sage is underwatered, it typically will recover quickly once it receives water.
Water sage fully to ensure it is reaching the root zone. You may also want to consider repotting the plant into a larger container if you are finding that the sage is constantly drying out much too quickly.
Most likely you have a pot that is too small to contain enough water for the sage to live successfully.
The recovery time period of an overwatered sage is going to take quite a bit longer with root rot:
- Utilize a moisture gauge or meter to determine how moist the soil is prior to watering again.
- Don’t water if the soil is dark-colored and moist; only water when it is dry and in the morning sun, so water will evaporate quicker and not remain in the wet for too long.
- Manually dig down into the soil a bit deeper to remove any moist soil, any rotten roots, and replace the soil in the pot with a new potting mix.
Humidity and Temperature Factors
In addition to watering and soil drainage issues, humidity in the air could cause black sage leaves.
Humidity in the air depends on temperature and wind speed.
Too much humidity, along with low temperature and little wind will result in reduced transpiration and air movement. The lower rate of evaporation will mean that the soil around the roots is likely to stay wet for longer.
Also, too dry air in high temperatures and too much wind around the plant leads to too much evaporation for the plant and results in either black leaf edges or the entire leaf is black.
Best Practice: Sage grows best in tropical areas of 150C – 210C, with relative humidity is 70%. Keep sage within this breathing zone of relative humidity and temperature.
Lighting Factor
Excessive sunlight or direct sunlight can also create black leaves or black tips.
Sage will adapt to medium sun exposure. If you have sage inside, place it on a windowsill that receives 6-8 hours of sunlight.
If it’s still not enough, consider installing growing lights.
Tropical sage is at risk of heat waves, so ensure they have some shading from either the direct sunlight or reflective surfaces.
Improper Fertilization
While fertilization is advantageous, it is not good to over fertilize.
Over application of fertilizer can cause a buildup of salts in the soil to develop, and can cause leaves to burn or turn black.
In addition to dialing down the amount of fertilizer applied, you can either replace a couple inches of topsoil with new potting mix, or you can flush the soil with water 4-5 times in the pot, allowing to drain each time, to remove the salt buildup.
Final Thoughts
A healthy sage plant has grey-greenish leaves; hence, you will see a noticeable difference when it begins changing to black leaves.
Proper sage care should take place at this moment, as the black leaves are the first sign before the plant will wilt and eventually die.
Prune the black leaves, and the rest of the plant can be placed in an ideal sage growing environment around 65–75 degrees to encourage new foliage to grow and not to further damage the plant.