Starting to notice yellowing or browning leaves on your zinnia plants? It might not be a sign of anything serious, but it’s something to take note of. Here’s why zinnia leaves are turning yellow and what you can do to prevent it from happening in the future.
Table of Contents
6 Reasons Why Zinnia Leaves Are Turning Yellow and Wilting
Poor Soil Condition
Many factors can contribute to poor soil conditions, including lack of organic matter, improper plant selection and planting techniques, insufficient water management, and over-irrigation. All these activities can drain the soil of essential nutrients and leach chemicals into the environment. Over time, this gradual process can damage the soil’s ability to retain moisture and support healthy vegetation. Bad agricultural practices such as chemical application or intensive grazing can also lead to declining fertility levels and increased pests and diseases.
Solution: To improve the soil condition, you’ll need to add organic matter, such as compost or leaves from dead plants. You can also water the garden less often to conserve moisture and help suppress weeds. Place plants in a location that receives full sunlight throughout the day. Finally, avoid using chemical fertilizers and pesticides unless your specific plant variety specifically requires it.
High temperatures can damage plants both directly and indirectly. Direct effects of high temperatures on foliage include sunscald, browning, and wilting. Indirect effects of high temperatures can include reduced flowering, root rot, fungal growth, stunted growth, and lower yields.
Solution: To prevent these problems, keep the garden temperature below 70°F (21°C) during the day and 45°F (7°C) at night. Mulch around plants to help retain moisture, reduce evaporation from the soil surface, and provide insulation against frosty weather conditions in winter. If necessary, plant varieties that are tolerant to cold weather conditions.
Incorrect Fertilization Schedules or Dosage Rates
Fertilization schedules or dosage rates can sometimes be incorrect, leading to poor growth and soil issues. When fertilizing your plants, it is important to use the correct amount of fertilizer for the plant’s stage in the life cycle.
Solution: The general rule is to apply 1 pound of nitrogen per 1000 square feet planted. If your plant is young (0-3 months old), you can lighten the nitrogen by half and still achieve satisfactory results. For plants older than three months but not yet four years old, full-strength nitrogen should be used at 1 pound per 1000 sqft. And finally, if a plant has been grown in organically rich soil for at least two years without any chemical nutrients, then applying organic matter alone will give sufficient nutrient levels.
If you are unsure about how much fertilizer to use or have other questions about fertilization schedules or dosage rates, please contact a local agronomist like Soils Unlimited!
Overwatering is one of the most common plant problems, and it can damage your plants. Overwatering occurs when the soil water supply is greater than what is needed by the plant. This excess moisture causes root stress, brown foliage, and a deficiency in key nutrients such as nitrogen.
Solution: While it’s not necessarily bad, you may want to take some steps to help remedy the situation. You can try watering your plants less frequently or using a rain barrel instead of relying on indoor plumbing. Additionally, you can add more mulch around the plant to keep moisture in and reduce evaporation.
Insufficient Amount of Nutrients
Nutrient deficiencies, especially in nitrogen, cause leaves to turn yellow. Nitrogen is essential for all plants and helps form amino acids, important nutrients for plant growth. When there isn’t enough available, yellowing will ensue as molecules in the leaf break down faster than they can be re-formed. This process requires energy and can be accelerated by high temperatures or low levels of light. A lack of iron can also lead to chlorosis—a condition in which the leaf cells become pale or straw-colored—and impaired growth. You can test your soil and water levels for signs of iron deficiency by using a ferrous sulfate supplement or soil test kit,
Solution: If you notice that your zinnias are exhibiting signs of yellowing (usually toward the tips), you may want to fertilize them more heavily with a nitrogen-rich fertilizer. Alternatively, reduce stress on the plant by keeping it out of direct sunlight and away from hot surfaces. Try supplementing its diet with a mineral nutrient such as magnesium or potassium nitrate if needed.
Pests and Diseases
By the end of summer, the leaves and flowers of zinnias are likely to turn an ashy gray color. This fungal disease gets worse when it is hot and humid. It usually shows up first on the lower leaves, especially when plants grow close together, cutting off airflow and increasing humidity. Many people don’t care about it because it doesn’t hurt the plant. It just doesn’t look good.
Solution: To stop the mildew from spreading, spray the leaves that are not affected with a garden sulfur fungicide according to the directions on the label. Look for zinnia varieties that don’t get mildew, like “Rose Pinwheel,” and space out the seedlings.
Verticillium Wilt Fungus
This fungus is a root disease that attacks zinnia plants from the soil up. It typically shows up as wilting of the foliage near the base of the plant and brown patches on roots or leaves. If you see this fungus attacking your zinnia plants, there’s not much you can do except removing infected plants and start fresh with new seedlings in some other spot in your garden.
Solution: Rid your garden of infected plants before planting new seedlings (cultural management). Fungicides will only kill fungal spores; they won’t help prevent verticillium wilt.
These little pests are attracted to zinnia flowers because their petals and leaves contain a lot of sugar. They lay their eggs on the plant, hatch into immature whiteflies that feast on the nectar, and then crawl off the plant to create more whitefly colonies elsewhere. Whiteflies can cause damage by sucking up sap from plants, leaving them wilted or yellowed; they also produce a sticky honeydew that can be difficult to clean.
Solution: Spray your zinnia plants with an insecticide according to label instructions; look for varieties resistant to whitefly attack. Trap and remove whiteflies using a yellow sticky trap or electronic traps.
They have soft, pear-shaped bodies and are about the size of a pinhead. There are green, brown, and pink ones. They tend to gather on tender, new growth on zinnia stems and the undersides of young leaves. They get their food from the juices inside plant cells, making the leaves curl, pucker, and yellow. Often, the leaves and flowers grow too short. Sometimes you can see ants crawling along the stems and leaves of plants. This is because the sticky honeydew that aphids make as they eat attracts ants. If there are aphids on the tips of your plants, just pinch them off and throw them away.
Solution: If they have infested a lot of the plant’s leaves, spray them with insecticidal soap from a store, following the directions on the label. Make sure the soap spray goes right on the aphids.