Reading The Leaves: 10 Causes And Cures For Foliage Problems

what causes foliage

The leaves on your indoor plants are trying to tell you something. When they're uniformly green, open, upright and growing vigorously, your plants are well-cared for and healthy. If, however, the foliage is wilted, spotted or in any way less than robust, your plants are likely to be suffering from a pest, disease, nutrient deficiency or other problem. With this quick guide on ten foliage problems, you can just check the symptoms you see, then identify the cause and learn how to solve it.




SYMPTOMS: Leaves develop yellow spots, then wilt. Black mold growing on top of leaves.

CAUSE: Aphids are tiny pests that can be red, green, black, brown or white. They cluster on the underside of leaves and suck the sap from them. This causes the yellowing and wilting. The pests also transmit viruses from plant to plant, which can lead to stunted growth. As aphids feed, they excrete a sticky substance referred to as "honeydew," in which black sooty mold grows.

QUICK FIX: Spray aphids with potassium salts of fatty acids (Safer® Brand Trounce Yard and Garden Ready to Use Spray), which weakens the pests' waxy protective outer shell and causes them to dehydrate. Be sure to target the pests on the bottom of leaves, too.

PREVENTION: Aphids produce as many 12 new offspring per day. Use insecticidal soap spray twice – once for the first application then 5 to 7 days later to get the next generation. Check underneath leaves every week to catch any new infestations.



Spider Mites

SYMPTOMS: Tiny pale specks on leaves or light, white webbing on leaves or buds.

CAUSE: Spider mites are minuscule relatives of spiders with four pairs of legs, no antennae and sharp mouths that pierce plant cells and suck out the fluids, leaving behind yellow, orange or white speckles. A single spider mite female can produce thousands of new mites in less than a month, so they can quickly become a real nuisance.

QUICK FIX: Isolate infested plants from others and spray them with a formula that kills the eggs and the larval stages as well as the adults. A blend of pyrethrins, a nerve agent made from chrysanthemums, and neem oil, a natural growth disruptor, combined with insect-killing soap, like our Safer® Brand Insect Killing Soap, wipes out all stages of the pests without harming plants, people or pets.

PREVENTION: Spider mites often spread from garden to garden on clones. Before bringing a new plant into your indoor garden, give it a thorough bath on tops and bottoms of leaves--spider mites need dry conditions -- and keep it isolated from others for a week while you check the underside of leaves for signs of the crawling pests or their tiny egg sacs.



SYMPTOMS: Silver or bronze colored streaks on leaves, which eventually turn brown, dry and crumbly.

CAUSE: Thrips are minute (less than 1/25 of an inch) insects that can be yellow, brown or black. To the naked eye, they look like tiny threads. The pests feed by puncturing plants and sucking out the sap inside, creating the streaks. Thrips also attack flower buds and can spoil your entire crop.

QUICK FIX: Spray affected plants with Safer® Brand End All Miticide/Insecticide Ready-to-Use Spray, which interferes with thrips' rapid growth by keeping them from molting properly. Repeat the treatment two to three times at 7- to 10-day intervals to ensure you've eliminated all of the pests and any new generations hatching.

PREVENTION: Check often for the presence of thrips by giving plants a gentle shake. The larva are wingless and will leap when jarred. Apply spray immediately when you see the pests to stop this fast-growing population.




SYMPTOMS: Stunted or twisted leaves, white spots or black moldy areas on the top of foliage.

CAUSE: Whiteflies are small, moth-like insects that cluster on the undersides of leaves. The nymphs are translucent and can appear to be the same color as the leaves. Both nymphs and adults suck the fluids from new growth, which causes fresh leaves to be stunted or twisted. Like aphids, whiteflies secrete honeydew that is colonized by black sooty mold.

QUICK FIX: Spray the pests and foliage with Safer® Brand Insect Killing Soap -- it stops the feeding and weakens the insects' natural protections.

PREVENTION: Whiteflies are drawn to the color yellow, so set up Safer® Brand Houseplant Sticky Stakes or sticky traps to capture them and help you monitor the pests. The traps alone can protect a few plants, but in larger indoor gardens they work best as an early warning system so you can notice an infestation before it spreads.



Powdery Mildew

SYMPTOMS: White to gray powdery coating, especially on young leaves. Blistered areas on leaf edges that causes them to curl upward.

CAUSE: Powdery mildew is a disease that shows up most prominently on new leaf growth. Flower buds may be white on the outside and never open. Eventually, severely infected leaves turn brown -- the coating blocks light from reaching them -- then drop. The fungi flourish in highly humid conditions and where there is little ventilation.

QUICK FIX: Apply Safer® Brand Insecticidal Soap to the tops and bottoms of leaves at first sign of the white fungus. The sulfur creates conditions that prevent it from growing and spreading.

PREVENTION: The dampness in indoor gardens are ideal for this fungi  Allow lots of room between plants so moisture can evaporate and use fans to create a gentle breeze that helps refresh air and keep humidity in check.



Nitrogen Deficiency

SYMPTOMS: Lower leaves look yellow and become soft and curl inward, then turn brown and crispy before falling off completely.

CAUSE: Nitrogen deficiency always affects the oldest (lowest) leaves first, because when new leaves aren't getting enough of the nutrient to sustain their growth, the plant redirects it from the existing leaves. As plants get close to harvest, it's normal for them to show signs of a nitrogen deficiency. At that stage, you want the plant to direct all of its energy into the fruit or flowers rather than growing new leaves. That's why "bloom" stage nutrient formulas are relatively low in nitrogen.

QUICK FIX: Give plants in their vegetative growth stage a high-nitrogen nutrient formula. Fertilizers made with fish tankage (decomposing processing waste) deliver a strong dose of nitrogen in a form that plants absorb and use quickly.

PREVENTION: A regular dose of an amino-acid supplement in your feeding program ensures that your plants always have access to all the nitrogen they need. Amino acids are building blocks of protein that help plants take up and use nitrogen.



Phosphorus Deficiency

SYMPTOMS: Lower leaves look dark green or bluish and appear shiny. May have splotches that look brown or bronze. Affected leaves curl downward.

CAUSE: Phosphorus deficiency usually shows up first at the bottom of the plant (on the oldest leaves) and progressively climbs up the plant if untreated. For many crops, the need for phosphorus peaks during the transition from vegetative growth to budding.

QUICK FIX: When your plants near their full-grown size add bone meal-based supplements, which are rich in phosphorus, to your regular feeding program and increase the dosage (following package instructions) as the buds begin to form. Bone meal is a natural source of phosphates in a form that plants absorb and use readily.

PREVENTION: Cooler temperatures and dramatic temperature swings can inhibit plants' ability to take up phosphorus. Keep the temperature in your grow room consistently between 65 degrees F and 75 degrees F.  



Potassium Deficiency

SYMPTOMS: Leaves all over the plants are yellow or brown, with tips and edges that appear burned, while the veins remain green.

CAUSE: Potassium deficiency can look like the lights are burning the leaves, but if your plants are at least 12 inches from high-intensity fixtures or you're using cool LEDs, the problem of burnt-looking leaves is a lack of K. Plants need high levels of the nutrient especially during their budding and flowering stages.

QUICK FIX: Switch to a high-potassium fertilizer during the budding phase of plants' growth. Molasses in the formula helps plants take up and use the potassium.

PREVENTION: Even if you are using a high-potassium "bloom" fertilizer, the plants may not be absorbing it all because the pH of the nutrient solution is too high. For soil-grown plants, be sure the pH is 6.0 to 7.0 and for hydroponic crops keep the pH to 5.5. to 6.5.



Heat Stress

SYMPTOMS: Edges of leaves curl inward and form a cup, even when the lights are off. The upper leaves are most affected.

CAUSE: Heat stress causes rapid evaporation, so plants curl up to conserve moisture. Plants too close to high-intensity lights are prone to heat stress, but it can be a problem in any room where temperatures are persistently above 80 degrees F.

QUICK FIX: Set up fans to blow out hot air and bring in cooler fresh air.

PREVENTION: Monitor the temperature not just in the room, but around the upper surface of plants. Maintain constant ventilation and allow sufficient space between plants and lights. 




SYMPTOMS: Drooping leaves, curling downward from the stem to the tip.

CAUSE: Overwatering is a more common problem in indoor gardens than under watering, but it is not always the result of giving plants too much moisture. Inadequate drainage of containers or watering hydroponic plants too frequently can also lead to the symptoms of watering.

QUICK FIX: Allow plants to dry out and then gradually increase water as plants recover.

PREVENTION: Water soil-grown plants only when the top inch of the soil is dry (stick your finger in it to check). Be sure excess water drains away quickly from plants' roots in pots or in flush-and-drain hydroponic systems. Don't put small plants in big containers, because the soil will hold extra moisture that the roots cannot absorb.

Keep Your Plants Safe and Healthy 

  1. Safer's® 3-In-1 Ready-To-Use Garden Spray - 1L
    Safer's® 3-In-1 Ready-To-Use Garden Spray - 1L
  2. Safer's® Insecticidal Soap Ready-to-Use Spray 1L
    Safer's® Insecticidal Soap Ready-to-Use Spray 1L
  3. Safer's® 3-in-1 32 oz. Ready-to-Use Garden Spray
    Safer's® 3-in-1 32 oz. Ready-to-Use Garden Spray
    As low as CA$14.19 Regular Price CA$14.19
  4. Safer's® Defender Garden Fungicide Ready-To-Use Spray III - 1 L - 1 or 3-Pack
    Safer's® Defender Garden Fungicide Ready-To-Use Spray III - 1 L - 1 or 3-Pack
    As low as CA$13.49 Regular Price CA$13.49
  5. Safer's® Ready-To-Use End ALL® Insect Killer
    Safer's® Ready-To-Use End ALL® Insect Killer
    As low as CA$14.79 Regular Price CA$14.79