One of our banana plants has some leaves that are turning black, and we weren’t sure how to fix it. So, I did some more research to find out. Here’s what I found.
Banana plants get black leaves from over-watering, cold weather, excess nutrients, and a disease called black Sigatoka. To help prevent black leaves, start by only watering when the top 2-4 inches of soil is dry. Also, avoid fast-release fertilizers and grow in USDA hardiness zones 9-11 if possible.
So, while banana plants get black leaves for several reasons, how can we tell which issue is causing it, and how can we fix it? Let’s take a closer look.
1. Over-Watering
Over-watered banana plants quickly get stressed, which leads to conditions such as yellow, brown, and black leaves. If not addressed, it can also lead to root rot.
The best way to water banana plants is to only water when the top 2-4 inches of soil is dry. You can check this by pushing a finger into the soil, under the plant’s canopy. By watering this way, you’re also preventing under-watering.
However, even if you’re watering banana plants correctly, they still can be over-watered if their soil has poor drainage.
Generally, banana plants prefer sandy soils since this is a common soil type found in the tropics.
More specifically, the ideal soil for banana plants is sandy loam. This means the majority of the soil is sand (52% or more), but enough silt, and clay (less than 20%), to hold nutrients and water.
| Soil Type | Pros | Cons |
|---|---|---|
| Sand | Good drainage | Doesn’t hold nutrients well |
| Silt | Holds nutrients well | Poor drainage |
| Clay | Holds the most nutrients | Even worse drainage than silt |
Because of this, avoid planting banana plants in heavy clay soil, or in pots with collapsed soil.
While clay contains many nutrients and minerals, it’s much finer than sand and can easily become compacted—not allowing water to drain (see the graphic below for comparison in size).
For planted banana plants with poor drainage, you can either amend the current soil with frequent applications of compost (2 inches every 1-2 months) or transplant the banana “pups” (new plants sprouting from the base) to a new location with better soil.
However, even though compost works its way into the soil and amends it, it can take some time. Because of this, I recommend transplanting any banana pups to a new location with improved soil.
If you don’t have a site with better soil, planting in a mound of soil or a raised bed is the next best thing.
By elevating the soil, gravity promotes better drainage by pulling the water out. A good way to do this is to make a banana circle (more on this later).
The goal is to maintain soil moisture similar to a wrung-out sponge.
Once your banana plant’s soil is well-draining, provide 2 inches of compost and 4-12 inches of mulch to provide sufficient nutrients, retain soil moisture, and keep the plant cool.
Reapply compost every 1-2 months and mulch every 3-6 months. Also, keep these materials at least 3 inches away from the banana plant’s stem to prevent mold buildup.
Pro-tip: Since banana plants die after fruiting once, chop and drop the main plant to use as mulch for any pups growing from its base. Many banana plant owners also selectively grow multiple pups at different stages from a single plant to have year-round fruit.
On the other hand, for potted banana plants with poor drainage, the best way to amend them is to repot the plant with fresh potting soil. Since the pot naturally confines the plant’s roots, there’s less of a risk of transplant shock (compared to uprooting mature banana plants in the ground).
2. Extreme Cold
Generally, the best climates for most banana plant varieties are tropical and subtropical USDA hardiness zones 9-11 (see the image and link above).
For best growth, keep banana plants between temperatures 70ºF to 90ºF (source).
As banana plants are natively from the tropics, they’re used to a warm climate, plenty of rain, and high humidity. Also, by evolving in these tropical forests as an understory plant, banana plants are used to plenty of partial shade and mulch.
However, problems arise when banana plants are grown in less ideal climates.
The worst climates for banana plants are those that are dry or cold.
Banana plants that are exposed to extremely dry or cold climates develop issues such as leaves drooping, browning, and blackening. If it gets too dry or cold, the entire banana plant can die.
The good news is that banana plants that have plenty of water, mulch, and shade can withstand quite a bit of dryness.
The bad news is that there’s not too much you can do about the cold.
Tips for Cold Weather
Banana plants stop growing when temperatures reach 48ºF and get discolored leaves and die when they reach 35ºF, but this depends on the duration they’re exposed to these temperatures.
For example, a temperature of 2°C (35ºF) will cause damage only if it lasts for longer than about 45 minutes.
Bananas-response to temperature, D.W. Turner, formerly Special Research Horticulturist Tropical Fruit Research Station
Here are some tips to keep your banana plants alive during cold weather:
- Bring potted banana plants indoors before frost arrives. However, make sure to keep it away from the central heat due to dryness (I learned this the hard way with my potted Meyer lemon tree).
- Grow in a greenhouse if possible.
- Provide heavy mulch to insulate the roots during a slight frost. Even if the main banana plant dies, there’s a good chance more pups will sprout from the root base.
- Grow cold-hardy banana plants such as Musa Basjoo, which can grow in USDA hardiness zones 4-11. However, this variety does not produce fruit.
3. Excess Nutrients
Since sandy soil has plenty of drainage and leach nutrients, it’s difficult to over-fertilize banana plants. However, it’s still possible.
Most commonly, excess nutrients are caused by fast-releasing fertilizers, as compost isn’t potent enough.
Excessive nutrients in the soil chemically burn the banana plant’s roots, leading to stress. This stress causes conditions such as leaves drooping, yellowing, browning, and blackening. However, this can be avoided with proper fertilizer practices.
How to Properly Fertilize Banana Plants
The two main methods to provide banana plants with nutrients are:
- Compost
- Chemical Fertilizers
However, many gardeners recently have been switching from fertilizer to compost. And they have a good reason.
While chemical fertilizers have nutrients in quantity, they typically lack nutrients in quality. For example, the nutrients found in synthetic fertilizers aren’t as bioavailable or absorbable as the nutrients in compost. Additionally, fertilizers often leave behind a crust on the top of the soil, drying it out.
Banana plants prefer soil that’s full of beneficial soil life such as earthworms and mycorrhizal fungi (mycelium). This beneficial fungi grows naturally in the soil of forests and provides many advantages such as greatly improved water retention, accessible nutrients, and disease resistance.
Mycorrhizal fungi promote many aspects of plant life, in particular improved nutrition, better growth, stress tolerance, and disease resistance.
Department of Biology, University of Fribourg, Switzerland
This boost in nutrients comes from mycorrhizal fungi trading nutrients found deeper in the soil (out of reach of the banana plant’s roots) in exchange for carbon (sugar) from the banana’s photosynthesis.
This is why mulch is so important for banana plants (and other fruit trees)—it simulates a fallen forest, providing nutrients and the medium for mycorrhizal fungi and mycelium to thrive!
Apply 2 inches of compost every 1-2 months and 4-12 inches of mulch to provide the ideal nutrients and conditions for banana plants to thrive. Benefits include dramatically increased water retention, nutrients, and disease resistance.
Not only are compost and mulch simply magic for banana plants, these materials regulate the soil’s temperature, helping banana plants thrive in slightly warmer or colder weather.
Pro-tip: Grow bananas in a banana circle for a better microclimate and nutrient cycling. Simply plant several plants in a tight circle and fill the middle of the circle with compost and mulch.
However, if you’d still like to use fertilizer, select one with double the nitrogen to phosphorus and potassium (NPK). For example, a 6-3-3 NPK works nicely. To see which fertilizers I recommend, check out my recommended fertilizer page.
The reason why banana plants are such heavy feeders of nitrogen is that they grow a lot more biomass than most other fruiting plants. Banana plants develop a whole new plant and fruit rack every 9 months.
Because banana plants have a soft stem and not a woody trunk, they’re technically an herb and can outpace the growth of fruit trees such as avocados.
But nitrogen isn’t the only nutrient to provide banana plants! Nutrients such as phosphorus are important for fruiting and other plant functions. However, most composts and fertilizers will have sufficient primary and secondary nutrients.
Soil pH
While nutrients are essential, banana plants also need a soil pH of 5.5 to 7.0 (source). Without it, banana plants develop growing issues and conditions such as black leaves.
This is because a slightly acidic pH is required to dissolve the solid nutrients in the soil.
Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants it must be dissolved in the soil solution. Most minerals and nutrients are more soluble or available in acid soils than in neutral or slightly alkaline soils.
Donald Bickelhaupt, Instructional Support Specialist, Department of Forest and Natural Resources Management
Two good ways to check your soil’s pH are either by using a pH strip or a pH meter. I prefer using a pH meter since they’re affordable and easy to use. To see which pH meter I use and recommend, check out my recommended tools page.
If you find that your banana plant’s soil is too alkaline (above 7.0) you can add acidic amendments such as coffee grounds, sand, and peat moss. On the other hand, if your banana plant’s soil is too acidic (below 5.5), add alkaline materials such as wood ash, charcoal, or lime.
Additionally, cold and/or wet soils are not good at promoting nutrient uptake as the banana plant will either be dormant during the cold or too stressed in wet soils.
4. Black Sigatoka Disease
Black Sigatoka (Mycosphaerella fijiensis) is a fungal disease that’s fairly common in banana plants. Leaves commonly get red-brown spots, before turning brown and black. The leaf areas just outside of the spots also turn yellow.
This disease quickly damages the banana plant’s leaves, which compromises its ability to photosynthesize—directly affecting the plant’s fruit size and overall health. Generally, this means a 30% to 50% loss of fruit and in some cases a complete loss of fruit (source).
Black Sigatoka is most common in tropical climates as the spores spread in warm and rainy weather. Unfortunately, banana plants also prefer tropical climates so this disease can be difficult to avoid.
Treatment
New leaves are the most susceptible to black Sigatoka, so catching this disease early on is ideal. The best ways to prevent and treat black Sigatoka are to:
- Choose black Sigatoka resistant varieties
- Intercrop with companion plants, such as alliums (garlic family)
- Use organic sprays
Companion planting bananas with other plants is becoming a popular practice as it’s found to have many benefits including pest and disease resistance. For example, intercropping with alliums has been found to alleviate Panama disease (the most destructive disease to banana plants, source).
Keep in mind that even though many sprays are labeled organic, they’re still found to have safety concerns.
If you’re interested, to give you a head start on some natural (and effective) ways to manage diseases with bananas and other fruiting plants, check out the two videos below.
Stefan Sobkowiak – The Permaculture Orchard has a great video on a safe, homemade, and most importantly—effective fungicide (hint: the secret ingredient is whey).
Mark Shepard, on his 100+ acre farm, uses a method called STUN (sheer total utter neglect) and it works wonders for him. He uses no chemical fertilizers, sprays, or any other dependencies. Through the struggle, his fruit trees become stronger and his job gets easier. In a way, it’s survival of the fittest for his plants.
