I grow basil for years and I have always wondered why basil dies so fast. Wilting, turning brown from the bottom up are all signs of a serious problem. What should you do then? Why is your basil dying? Here is what I noticed over the years of growing basil indoor and outdoor.
The most common reasons for dying basil plants are 1) overwatering and 2) insufficient light. Other reasons for basil dying are also 3) aggressive pruning 4) natural end of life 5) inadequate temperature 6) humidity issues 7) lack of nutrients 8) excessive fertilizer 9) inadequate container 10) pathogen.
Figuring out what is wrong with your basil plant is the first step to understanding what you can (should not) do to fix it.
Table of Contents
- 1 10 Common Reasons For a Dying Basil
- 2 FAQs
- 3 Takeaways
- 4 Sources
With enough water and sunshine, you can grow basil in a pot on your kitchen window sill. You can pluck leaves for an immediate cool touch in iced tea, salads, or in comfort soups and dishes.
When basil stems or leaves turn brown or black, you may be looking at a natural process or it may be an indication of a serious problem. Here’s a summary of what you should know.
To begin on a bright note… in many cases, when basil stems are turning darker in color, it’s a natural process that is not a cause for worry. However, quite often, if you are a beginner gardener, you might fall into one of these pitfalls.
1. Excessive Watering
Overwatering is by far the cause number of one of dying basil. When basil gets too much water – or poorly drained soil – the fungal disease can cause root decay and root rot, also known as “damping off”, which kills the plant.
Overwatering symptoms include wilting leaves, darkening stems, and spongy, smelly roots. One effective strategy is to let the soil dry out (but not bone-dry) between waterings.
Overwatering: To manage root rot and water drainage, just buy a good planter with drainage holes (here one in Amazon) or mix the soil with some perlite like this good one on Amazon. I recommend one-third of perlite per volume of potting mix.
Despite being rarer among beginner gardeners, under-watering can cause drooping, wilting, and stems drying out and turning darker in color. Severe underwatering can cause basil plants to die.
Underwatering: Basil underwatering is way easier to recover than overwatering. You just need to water the plant again!
2. Inadequate Light
Another cause of dying basil is the lack of adequate light or an excessive amount. Basil needs an average of 7 hours of direct sunshine. However; in hot climates such as in the South and Southwest parts of the USA, basil plants should be shaded in the afternoons when it’s too hot otherwise you will end up with a sunburn.
In case the basil receives less than 7 hours of light a day a good grow light is recommended. The 60-Pc 10W Full Spectrum LED Grow Light for Indoor Plants is a good choice for a single plant.
A cool fact!
Basil needs different night and day temperatures (thermoperiods). You see, if you grow basil with a temperature that is constant all the time, it won’t grow well. That’s because, when day turns to night and temperatures drop to between 64.5° and 71.5 °F (or 18° to 22°C), basil plants manufacture highly flavored and aromatic oils.
3. Aggressive Pruning
If a basil plant is pruned too heavily by removing most of all the leaves then the plant will probably not be able to continue its photosynthesis activity and slowly die. In general, less than two-thirds of the stems should be harvested to avoid killing a basil plant.
When you pluck leaves or cut off leaves, branches, or flowers from your basil plant, the “wound” is a trauma that tries to heal itself. The trauma seals itself and shows a darker brown color.
If the stems are without leaves, there is nothing that can be done. Based on my experience I suggest waiting. If the plant recovers, then next time follow the guide on how to prune basil the right way.
4. Natural End of Life
Basil that has been growing for more than 10 months will start flowering and dying. This is normal as basil is an annual plant that lasts at most 10 months in ideal conditions.
Despite basil cannot being turned into a perennial plant, its dying off the process can be slowed down by pruning off all the flowers before they fully form. This will give a signal to the plant that it “needs” to last longer in order to fulfill its role. This is a survival mechanism that works in many herbs. This can extend the lifespan by a few weeks.
5. Inadequate Temperaure
Basil leaves will start dying when the temperature drops below 50°F or 10°C. Basil leaves turn dark and die.
Basil originally comes from the tropics of Southeast Asia and Central Africa. It can thrive in temperatures as high as 90°F (32°C). Some types of basil can grow at 43°F or about 6°C. The ideal temperature for your basil is between 72.5° and 82.4°F or from 24° to 28°C. Indoor gardeners agree that this temperature range gives you maximum harvest for indoor basil plants.
In case basil is wilting due to low temperature, the ideal is to place it inside or in a warmer (not humid) place in the house. Basil dying for frost damage can still be saved if placed quickly indoors.
6. Excessive Humidity
In general, basil tends to die easily if exposed to air with a humidity level of 65% or above. This is often the case when basil is placed close to the kitchen sink. The evaporating hot water will expose the basil to very moist air, triggering the uptake of fungi development and other diseases.
Dying basil due to humidity issues can be easily saved by placing it in a drier location (avoid the kitchen or bathroom, even if you have a large window) and placing it in front of a large windowsill far from a kettle or any other water source that can evaporate.
In case developed any kind of mold or fungi (white spots) please check the next sections.
7. Lack of Nutrients
One reason why your basil plant can turn dark brown/black and dye off is the lack of phosphorus. Despite this being a rare reason it might still happen if a poor or overused potting mix is used.
To integrate the lack of phosphorus you can use a rock phosphate fertilizer like this one or a bone meal feed for plants like this one. Remember that bone meal might smell quite strongly, so avoid it indoors.
If you want to know the details on nutrient deficiency/excess, check our full guide on nutrients.
8. Excessive Fertilizer
Dying basil, in general, can be easily triggered by excessive fertilization, or fertilization done at the wrong time. This will cause also the accumulation of salt that will literally dry out the plant despite the regular watering.
The mineral salt ions in inorganic and synthetic fertilizers are not all absorbed by plants. Instead, they remain in the soil and these fertilizer salts (no, they’re different from table salt) slowly accumulate in the soil. More fertilizer means more salinity in the soil, which can kill plants.
Basil in general needs little fertilizer, and mainly just before the summer season. In case of excessive fertilization, the best way is to replace the soil with a fresh one. This will remove the fertilizer built up into the soil.
Another solution for a salt buildup in basil as well in any plant is flushing or leaching the soil with running water can help remove salt buildup.
9. Inadequte Container
Basil plants are usually sold in small containers. However, if the planter is not upgraded to at least 8 inches, this might slow the basil development or cause an early flowering and dying.
Basil is often sold as a bunch of small plants that need to be repotted as they grow. Failure to repot, using too-small pots, or planting too many in a pot can severely restrict the space for root growth and development. When roots can’t draw in enough water and nutrients, or when roots are unable to spread, plants become unhealthy and the plant can struggle to grow.
Just a larger pot for your basil (plastic or ceramic) will do the trick!
Basil might wilt and start dying if attacked by any fungi or diseases. The most common on basil are 1) fusarium wilt 2) downy mildew 3) mint rust fungus 4) southern blight 5) bacteria leaf spot 6) cerespora leaf spot.
Most of these problems are associated with black spots on basil leaves.
Fusarium Wilt – A fungus in the soil or seeds of infected basil plants can infect your basil with fusarium wilt. Symptoms include brown spots or streaks on the stem, severely twisted stems, stunted growth, wilted and yellowing leaves, leaf drop, and the plants eventually die.
Downy mildew or gray mold – When basil turns black, it may be caused by the Peronospora belbahrii pathogen found in contaminated seeds, infected transplants, or wind-borne spores. Green leaves turn yellow, with dark gray or purple fuzzy growth underneath.
Mint rust fungus – For those who grow mint, rust fungus is a disease caused by the Puccinia menthae fungus.
Southern blight – Also known as southern root, southern stem rot, or southern wilt, this disease causes basil to wilt and die. When soil is moist and warm in summer, the Sclerotium rolfsii fungus spreads a network of white filaments (hyphae or mycelia) around the lower stem and roots of basil. You will see leaves wilting, lower leaves are discolored, and the plant dies.
Bacterial leaf spot or Basil shoot blight – Caused by the fungus Pseudomonas cichorii, this disease causes dark streaks to appear on the stems of older basil plants as well as leaves spotting and dropping off.
Cerospora leaf spot or Circular leaf spot – This disease shows as dark brown spots and is caused by the fungus Cercospora ocimicola often due to too much moisture on the leaves. The problem often appears in the rainy season, or in plants with too high moisture and poor air circulation.
These pathogens can be avoided by spacing plants far apart to provide good air circulation, and low moisture to keep leaves dry.
Some gardeners recommend the use of products containing thiophanate-methyl, myclobutanil or chlorothalonil. Others prefer to use baking soda mixed with light horticultural oil, while a few others prefer to use sulfur or neem oil.
How long will it take for my basil to regrow? Regrowing basil can take any time from 2 up to 4 weeks. The secret is this: trim, cut, prune your basil so that one cut stem grows to new stems. Cut those, and double the number of stems again and again.
How do I know if my basil plant is overwatered? The signs of an overwatered basil plant include roots that are black or brown and roots that are soft (mush) and smelly. For a full guide on how to water basil check the full guide on basil watering.
Fungus attacks can cause stems to discolor or show dark streaks or blotches while bacteria attacks cause dark spots.
If you water your basil too much, the roots will rot and the leaves will droop. Too little water and the soil will dry up and the plant will die. Take time to learn just how much water is right for your plant.
Prevention is a primary strategy. Buy disease-free plants. Use clean soil and pots when potting, repotting, or transplanting.
Also, take time to provide your indoor basil plants with the correct conditions for healthy growth, and check them often for any of the problems summarized here.
Do these, and you’ll be a happy gardener with happy houseplants.
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“Circular leaf spot of sweet basil caused by Cercospora guatemalensis new to Japan” by J. Nishikawa, et al in Journal of General Plant Pathology