Why Your Garden Plants are Turning Yellow and How to Fix it

Yellowing leaves are a distress signal from our plants that something’s not quite right. It shows a disruption in chlorophyll, the compound responsible for the green portion of leaves. Behind the scenes, normal plant processes aren’t functioning to fully serve the plant. 

Yellowing signals a number of factors. It can be a natural part of aging, where mature leaves drop to make way for new growth, or as plants prepare for winter dormancy. It can also be a response to environmental stressors that aren’t a match for ideal growing conditions. A little scouting shows us the direction to take to remedy the cause.

Fortunately, plants turning yellow give us a visual cue so we can monitor and adjust care protocols to restore health. Often, a straightforward adjustment in cultural conditions does the trick.

Here, we’ll explore what to look for to determine the cause and remedy for yellowing leaves to return our plants to glory.

Over or Underwatering

Not to confuse the issue, but yellowing, wilting leaves result from both too much and not enough water. Excessive irrigation or prolonged rainfall causes saturated conditions. Or, a dry spell or lapse in watering may happen. Fluctuations between wet and dry conditions also cause stress (watering too much to overcompensate for skipped sessions, for example).

With too much water, leaves turn a brownish-yellow and become soft, limp, and wilted. With a lack of water, yellowing leaves are more rigid, crispy, and even cracked.

To determine if either under- or overwatering is the cause of plants turning yellow, a simple soil touch test lets us know if conditions are too wet or dry.

If the soil feels slick and sticks to your fingers at an inch or two deep, oversaturation may be the issue. Decrease irrigation if the soil remains overly wet. Powdery, dry, or crumbly soils indicate a lack of water. Adjust as the plant preferences warrant to meet their ideal moisture needs.

Plants benefit from regular deep watering sessions rather than frequent, shallow irrigation. Watering deeply ensures the roots and surrounding soil absorb moisture for steady uptake and deeper root growth.

Poor Soil Conditions

Since soil is the foundation for plant health, it helps to check the conditions when plants turning yellow is a concern. A soil test is a good option to determine soil nutrient and pH levels, and any necessary amendments to meet plant needs. A local university extension office or an at-home kit assesses soil needs for the best health. 

Many of our favorites, from houseplants to flowering shrubs, prefer organically rich loams with good drainage. Others tolerate rocky or sandy conditions and various other compositions, including lean soils. 

Clay, compacted, or poorly draining soils are a challenge without compost or other amendments. Leaves may yellow, wilt, and droop as roots sit in water, unable to uptake moisture or nutrients to support the upper growth. They also lack access to oxygen in poor soils with standing water.

Soil pH also causes yellowing when it’s off kilter for the specimen. Soil pH relates to alkalinity and acidity levels, and those that are too high or too low block nutrient availability to the roots. Leaves may become chlorotic due to iron deficiency and the inability to absorb necessary elements.

Lack of Nutrients

Some hardy plants prefer lean soils or don’t need additional fertilizer with compost as an amendment. Others may turn yellow as a sign of a lack of nutrition. Leaves that are entirely yellow can indicate a lack of nitrogen, or yellow-brown margins and veins can indicate a lack of potassium and magnesium.

If plants are turning yellow, especially with slowed growth, and watering or soil drainage doesn’t seem to be the issue, it may be a nutrient deficiency. An application of a balanced slow-release fertilizer may help restore vigor. Low-grade organic options include fish emulsion, seaweed extract, and alfalfa.

Conversely, too much fertilizer exacerbates yellow and browning leaves. Excess nitrogen leads to plants producing more prolific but weaker and less healthy leafy growth. With too much fertilizer, leaves turn yellow and brown before becoming crisp and dropping. With overfertilizing, plants turning yellow may correct themselves as the fertilizer runs its course, with regular irrigation and rainfall.

Temperature Stress

Sudden heat waves or cold snaps are extremes that can also lead to plants turning yellow. In high heat, leaves tighten, and stems wilt to conserve moisture and energy. Many rebound with moisture and as temperatures moderate in the evening.

Others, who show leaf decline, need a protective shade cover to combat prolonged high temperatures. Shade cloth, an umbrella, or other temporary screens offer cooling protection against hot rays. Move stressed container specimens to dappled light or afternoon shade until the heat passes.

Provide a two-inch layer of mulch year-round to insulate roots throughout the seasons. Mulch helps regulate soil temperatures and retain moisture.

Sun Exposure

With exposure to intense, burning rays and heat, leaves and fruits get sunburned. With sunscald, bleached, whitish patches appear on the foliar surface. The blisters become dry and papery as the tissues die.

At lower temperatures, minor cases present as yellowish or brownish, crispy spots on the leaves. Edges and in between veins are likely to show damage on foliage.

Make sure the plant is in the right garden location according to its preferred exposure to prevent too much sun. If a hot spell is an anomaly, offer temporary protection like shade cover and increased moisture.

Let any sunburned leaves stay in place as long as they show some green. The healthy, chlorophyll-filled tissues continue photosynthesis to support the rest of the plant as it recovers. The leaves continue to shield the underlying leaves and fruits, and removing them exposes new growth to the rays and heat.

If plants turning yellow show signs of disease, like dark spots or a powdery coating, fungal, bacterial, or viral pathogens may have set in due to the wounds. Clip them off to minimize the spread.

Aging

As part of their life cycle and varying growth phases, plants may drop leaves that no longer serve vital processes or that they can no longer support. As older leaves become shaded by new, upward-reaching growth, they may yellow and shed.

Seasonal fatigue after expending high amounts of energy during the growing season can show as yellowing. Growth slows in preparing for overwintering.

Pests

With cultural conditions covered, the source of plants turning yellow moves to pest scouting. Common garden pests, especially sap-feeding insects, cause leaf damage in severe infestations. They can also be vectors for diseases.

For each of the sap suckers on our list (which is much longer in terms of garden offenders), the treatment approach is similar. Spray plants with a strong stream of water early in the day to displace the insects from leaves and stems. A simple horticultural soap or neem oil treats infestations. Be sure to follow label directions, as these treatments also affect pollinators and other insects.

Predatory insects like parasitic wasps, green lacewings, and ladybugs feed on aphids and other pests. Grow a variety of pollen and nectar-rich plants to increase biodiversity and boost natural pest control.

Aphids

Aphids have a wide palette and feast on numerous ornamentals and edibles. The soft-bodied insects colonize on the underside of leaves and reproduce quickly. In high numbers, they can cause stress, but most damage is due to their spread of diseases. They also leave behind a sticky honeydew that can lead to unattractive black, sooty mold. 

If you notice curled, yellowing leaves, stunted growth, or signs of the insect itself, opt for treatment.

Spider Mites

Spider mites, too, feed on tissues and gather on the undersides of leaves. You may see webbing, leaf yellowing, and stippling on leaf surfaces. Foliage may become stiff and curl or prematurely drop, and flowers can discolor.

Spider mites occur in hot, dry, dusty conditions, especially on plants experiencing drought stress. Keep up with watering to avoid dry spells and drastic moisture fluctuations.

Prune away affected parts, and dispose of the debris rather than adding it to the compost pile, which can harbor and spread the insects. Try the water spray option as an initial treatment.

Scale

Scale are cottony insects that usually appear beneath leaves and along stems as black, gray, or silvery dots. In heavy infestations, leaves may turn yellow and drop, and branches die back. 

If the infestation is severe, remove the affected leaves and branches. Horticultural oils may need repeat application to fully rid the plant of the pest. For isolated, early populations, wipe stems and leaves with a cotton swab dipped in isopropyl alcohol (70% or less strength). While not feasible for large specimens or populations, the technique quickly reduces early numbers. 

Diseases

Disease is another cause of plants turning yellow. Whether fungal, bacterial, or viral, pathogens have different hosts and ways of spreading. Many spread easily through soil, wind, tools, and splashing water. Diseases may infiltrate leaves, stems, and roots, depleting the plant of nutrients and energy.

Root Rot

Root rot occurs most often in warm, humid environments and overly wet situations. The pathogen Phytophthora, among others, impacts feeder roots, which become unable to absorb water and nutrients for the upper growth. Signs of root rot include drought-stressed leaves that turn yellow and wilt. 

Check for rot by inspecting stems slightly below the soil line. Decaying stems will be yellow or brown. Roots, too, appear brown rather than a healthy white.

Plants may recover from rot with early detection and by altering cultural conditions. Dig plants to cut away any brown, rotting roots. Reduce the irrigation frequency to allow the soil time to drain. Water deeply as needed in accordance with the selection’s moisture preferences.

Powdery Mildew

Powdery mildew thrives with a lack of air circulation. The fungus Erysiphe, among others, pops up as a grayish-white powdery coating on leaves, stems, and buds. Leaves turn yellow, distort, and drop during severe infections.

The fungal spores spread by traveling on the wind, gaining garden entry with infected plants, unsanitized tools, and splashing up from the soil via raindrops and irrigation. The spores start on the leaves in spots and patches and spread to the stems, depleting the host of nutrition. 

Fortunately, powdery mildew is treatable with early detection. Handpick and remove the infected leaves when possible. Horticultural oils can treat the fungal disease early on and prevent spread to healthy tissue.

To prevent powdery mildew, practice good irrigation by avoiding wetting the leaves when possible. This limits damp conditions and helps keep spores from splashing up from the soil and spreading.

If using overhead irrigation, water early in the day so foliage dries in the sun. Proper spacing at planting allows air circulation around leaves and stems. Prune away encroaching foliage to stave off powdery mildew.

Rust

Rust is another disease prone to hot and humid climates. Leaves may yellow, wilt, and drop early. 

With rust, red lesions may appear on stems, or powdery spores crop up on the undersides of yellowing leaves. The spores erupt to spread between plants. Remove any infected leaves or stems and discard them in a garbage bag or burn pile.

Horticultural oils can treat the fungal disease with early detection. For plants in decline, cutting back stems to the ground and checking for fresh growth or removal is the best action.

The best way to prevent rust is to increase air circulation, especially in humid conditions. Watering at the base of the plant delivers moisture to the roots without splashing foliage or fostering a damp crown.

Downy Mildew

Downy mildew, or Peronospora pulveracea, causes grayish-white lesions on leaves and blooms. The spores begin on the leaves and spread to other plant parts. Foliage turns yellow, distorts, and drops during severe infections. The fungus spreads quickly, and if left untreated, plants wither and eventually die.