Grass Turning Purple: Pollution's Impact On Nature

Grass turning purple is not an uncommon sight, and it can be caused by several factors, including pollution. While ornamental grasses are often purple, it can be concerning when the grass on your lawn, which should be green, starts turning purple. Grass can turn purple due to nutrient deficiencies, water stress, extreme temperatures, diseases, pests, and environmental factors like pollution or chemical contamination.

Air pollution

Grass turning purple is not an uncommon occurrence and can be caused by several factors, including environmental ones such as air pollution.

Causes of Purple Grass

One of the main reasons grass turns purple is due to nutrient deficiencies, especially a lack of phosphorus or potassium. These nutrients are essential for the production of chlorophyll, which gives plants their green colour. A lack of chlorophyll will cause the grass to develop a purple tint.

Purple grass can also be caused by cold weather stress. Cold temperatures impair the grass's ability to absorb phosphorus, resulting in a colour change. The freezing weather, combined with a lack of water, puts stress on the grass, which can lead to purple blades.

Additionally, water stress, which can be caused by over or under-watering, can also contribute to grass turning purple. Inadequate water uptake prevents nutrient absorption, leading to purple grass leaves.

Preventing and Treating Purple Grass

To prevent grass from turning purple, it is important to establish a consistent watering schedule based on the grass's needs and environmental conditions. The soil should be adequately moist but not waterlogged, as overwatering can also lead to purple grass.

If your grass has already turned purple, there are a few things you can do to treat it. If the issue is caused by cold weather, you may need to wait for warmer temperatures to return before the grass turns green again. However, if the problem is due to phosphorus deficiency, applying fertiliser to your lawn can help ensure your grass receives sufficient nutrients.

Chemical contamination

Grass turning purple is not an uncommon sight and can be caused by many factors, including environmental ones like pollution and chemical contamination.

Additionally, promoting soil health through organic amendments and proper waste management can enhance grass resilience to environmental stressors. Conducting regular soil tests will help monitor pH levels and ensure they remain within the optimal range for healthy grass growth.

It is important to note that grass can turn purple due to various reasons, including nutrient deficiencies, acidic soil, water stress, extreme temperatures, diseases, pests, and environmental factors. Proper diagnosis and treatment are crucial to address the underlying cause and restore grass health.

Nutrient deficiencies

While grass turning purple can be caused by several factors, including cold weather, disease, and environmental factors like pollution, nutrient deficiencies are a common cause.

Grass requires various nutrients to stay healthy, and a lack of these nutrients can lead to discoloration. Nutrient deficiencies can hinder the grass's ability to produce chlorophyll, resulting in purple or reddish hues in the leaves. Phosphorus and potassium are two essential nutrients that play a vital role in chlorophyll production. When grass lacks these nutrients, it may turn purple.

Phosphorus

Phosphorus is crucial for the carbohydrate transport system, which provides energy to all parts of the plant for growth. It is also essential for root development and increasing stored carbohydrates. A deficiency in phosphorus can cause older leaves to turn dark green with reddish-purple pigmentation along the margins.

Potassium

Potassium is important for regulating water within the grass cells and increasing tolerance to heat, cold, drought, and pests. A deficiency in potassium can cause interveinal yellowing, leaf tip burning, and necrotic spots on leaf margins.

Nitrogen

Nitrogen is required in high amounts by turfgrass and is essential for color, growth rate, density, pest occurrence, and stress tolerance. A deficiency in nitrogen can cause yellowing and stunted growth, usually affecting older leaves first.

Calcium

Calcium is necessary for cell division and cell membrane permeability. It is relatively immobile and is typically found in older leaves. A deficiency in calcium can cause younger leaves to become distorted, twisted, or deformed, eventually leading to leaf margins and tips withering and dying.

Magnesium

Magnesium is a component of chlorophyll and is involved in carbohydrate and phosphate metabolism. A deficiency in magnesium typically occurs in acidic sandy soils and can cause a slight discoloration of the lower leaves, followed by interveinal chlorosis, and eventually blotchy-red older leaves.

Sulfur

Sulfur is required for protein synthesis and is used in the production of proteins and chlorophyll. Deficiencies in sulfur often occur on soils low in organic matter, and symptoms include pale, yellowish-green leaves, particularly on newer leaves.

Iron

Iron is commonly deficient in turfgrass, and a lack of it can cause interveinal chlorosis, with newer leaves eventually turning white. Iron deficiencies are typically more severe on closely mowed turf, impacting the grass's aesthetics.

Manganese

Manganese is involved in photosynthesis, carbohydrate metabolism, chlorophyll synthesis, and enzyme activation. A deficiency in manganese can cause interveinal chlorosis on new growth and necrotic spots on older leaves.

Copper

Copper plays a role in producing enzymes used in plant metabolism and is connected to the light reaction during photosynthesis. A deficiency in copper can cause chlorosis of new leaf tissue, with bluish tips turning yellow and necrotic.

Zinc

Zinc is important for the synthesis of plant hormones and auxins that promote growth. A deficiency in zinc can cause a mottled, chlorotic appearance with rolled leaves.

Identifying and Addressing Nutrient Deficiencies

Soil testing is crucial to identify specific nutrient deficiencies. It is recommended to test the soil every three years and take multiple samples from different areas of the lawn to get an accurate picture. If you notice any visual symptoms of nutrient deficiency, such as discolored leaves or stunted growth, it is important to take isolated samples from those areas.

Once a nutrient deficiency is identified, you can take appropriate corrective actions, such as applying fertilizers, adjusting watering practices, or treating lawn diseases.

Extreme temperatures

During sunny fall days, when temperatures fall below 50°F (10°C), grasses experience "low-temperature photoinhibition." They require less light and heat for photosynthesis as they prepare for dormancy. If they remain exposed to moderate light intensity (around 800 micromoles per square meter per second) in conjunction with low temperatures, they become stressed and exhibit photoinhibition. As a result, the grass starts building up anthocyanin levels and turns purple.

This phenomenon also occurs in spring when the snow melts and the sun appears. The grass, which has been shaded during the winter, now faces an onslaught of powerful sunbeams while recovering from cold stress. The sudden exposure to intense sunlight, coupled with the previous cold stress, triggers the production of anthocyanins, leading to the grass turning purple.

The purple discolouration is a cosmetic issue and does not indicate any serious problem with the grass. In fact, the higher anthocyanin levels provide sun protection and help the grass adapt to seasonal changes. However, it is important to note that extreme temperatures can also affect grass in other ways, such as impairing its ability to absorb nutrients, which can lead to nutrient deficiencies and further contribute to discolouration.

Diseases and pests

Grass turning purple is often a sign of stress, which can be caused by various factors, including diseases and pests.

Diseases

Grass can be affected by a range of fungal diseases, which can cause discolouration and damage. Some common lawn diseases include:

• Dollar spot: This disease affects golf courses, athletic fields, lawns, parks, and institutional grounds. It appears as a foliar disease with purplish-black borders, and the crowns and roots turn dark brown to black.
• Powdery mildew: This fungus typically appears as a white to light grey powder on grass blades but can sometimes turn purple. It thrives in warm and humid conditions and can spread quickly if the lawn is not properly cared for.
• Brown patch: This disease is characterised by yellow, tan, or brown rings or patches of sunken grass, up to 3 feet in diameter. It usually occurs under humid conditions and affects the crowns, stems, and leaves of plants.
• Leaf spot: This grass fungus is caused by Bipolaris sorokiniana. It is distinguished by brown and purple spots on the grass blades. If left untreated, it can destroy your lawn by travelling down to the roots and causing them to rot.
• Red thread: This disease thrives in cool, humid conditions and is commonly found in lawns with nutrient-poor soils. It is identified by thin, red hairs or strands extending from the grass blades.
• Rust: This group of foliar diseases can occur on golf courses, athletic fields, lawns, parks, and institutional grounds. It appears as irregular light green or yellow patches, with orange-yellow rust spores visible on individual grass blades.

Pests

Lawn pests can cause significant damage to your grass and should be identified and treated promptly. Some common lawn pests include:

• Grubs (Beetle Larvae): Grubs are the larvae of various scarab beetles, including masked chafers and Japanese beetles. They feed on lawn grass roots just below the soil surface. Signs of grub damage include wilted grass blades, brown turf patches, and eventually, dead grass.
• Chinch bugs: These sap-sucking insects feed on grass, causing it to stop absorbing water. As a result, the grass withers and dies, often mistaken for drought stress. Chinch bug damage is visible from June to September, with irregular patches of turf taking on a purple tinge before wilting and turning yellow and brown.
• Sod webworms: These are the larvae of lawn moths that feed on grass leaves at the root level. They can cause extensive damage, leaving behind brown patches and silken tunnels at turf level.
• Armyworms: These pests eat grass blades and stems, creating circular bare spots in lawns. They vary in colour from gray to yellow to pink, and they turn into brown moths that are visible at night.
• Cutworms: These pests shelter in underground burrows during the day and emerge at night to feed on the base of grass, biting off stems. They primarily affect short grasses, leading to dead spots in the yard.

Frequently asked questions