Spinach plants are leafy green flowering plants of the family Amaranthaceae. The vegetable leaves are consumed fresh or preserved, and may be eaten cooked or raw. These annual plants are native to Central and Western Asia and can grow as tall as one foot. They are cold-hardy and can tolerate low temperatures but, like most plants, they can also suffer from yellowing leaves.
Spinach leaves turning yellow: Common reasons
Spinach needs to be planted in nutritionally balanced soil. To check the nutritional levels of the soil, use a soil testing kit. This will also measure the pH level and other components such as phosphorus and nitrogen. If the soil has insufficient nutrients, the leaves will tend to turn yellow.
These plants need a pH level of 6.2 to 6.8, and if your soil is too alkaline the leaves may turn yellow. Furthermore, if the spinach plants lack nitrogen, phosphorus, boron or potassium, the leaves will also turn yellow.
To fix the problem, add compost to balance the pH and nourish the soil. To bring the pH below 7 and add more acid to the soil, you can use lime or fresh coffee grounds.
Spinach plants are heavy feeders requiring nutrient-rich soil. All-purpose fertilizers and compost should be added before planting to ensure that the soil is nourished.
If the plants are already established but the leaves are turning yellow, they may be lacking nitrogen. Apply a nitrogen-based fertilizer directly to the surrounding soil, or dilute it in water and apply it through watering.
Spinach leaves can also turn yellow due to diseases and infections. Below are just some of the common diseases that affect spinach:
1. Mosaic virus
This is also called blight, and is a condition that starts with yellowing leaves. As it progresses the leaves curl inward, becoming thin and wrinkled with distorted growth. The infection is transmitted from one plant to another by insects like aphids, leafhoppers and cucumber beetles. There is no treatment, and you need to destroy the affected plants to prevent the spread of the disease.
To protect your spinach plants from further infection, use insecticidal soaps and safe vegetable insecticides to prevent pests like aphids, harlequin bugs and leafhoppers.
2. Beet curly top
Spinach plants with this disease will manifest light green and then yellow leaves, starting with the younger leaves which become curled and deformed. The veins become purple and the texture becomes stiff and thick. Insects like leafhoppers transmit the disease in warm conditions, and you need to destroy the infected plants to avoid the spread of infection.
Use pesticides to prevent and control pests, so that there will be less chance of the plants becoming infected with this disease.
3. Root rot
Spinach plants that are starting to wilt with stunted, yellow leaves indicate that they are suffering from root rot, which is also called damping off. The roots become discolored and water-logged, with necrotic lesions. Older plants may die suddenly, while seeds will not germinate properly.
Root rot is caused by fungus resulting from too much water in the soil. Avoid watering the plants too much and make sure there is proper soil drainage so that water does not stay stagnant in the soil. Use safe vegetable fungicides to treat and prevent further outbreaks and do not plant spinach in the same area repeatedly.
4. Aster yellows
Spinach afflicted with this disease manifests yellow leaves and stunted growth. There are signs of chlorosis, or yellow leaves with green veins, and the color may change to red or purple. This disease is transferred by leafhoppers that feed on the plants and suck out the nutrients.
There is no treatment for this infection, and the infected plants should be destroyed to prevent it spreading. Use insecticides to prevent pests and keep your gardens free of weeds to reduce the chances of reinfection.
5. Fusarium wilt
Yellowing spinach leaves may also be an indicator of Fusarium wilt. The pathogen responsible for Fusarium wilt fungal disease is Fusarium oxysporum. The disease usually causes the plants to become wilted and withered, starting from the base. Prune the infected plant parts, use fungicides, and do not compost infected plant materials to avoid the spread of the disease.
6. Downy mildew
Yellow spots and fuzzy gray material on the underside of the leaves indicates that the spinach plants have downy mildew. This name refers to several types of oomycete microbes that are obligate plant parasites. Prune the infected leaves and discard them at once to prevent the infection from spreading.
Water the plants at the base rather than from overhead, to keep the leaves dry, since downy mildew thrives in moist conditions. Do not plant the spinach too early or too late in the growing season to avoid infection. You can also opt to plant spinach varieties that are resistant to downy mildew, such as St. Helens, Meridian and Olympia.
Overwatering or underwatering
Spinach plants require water to survive, and if they do not receive enough they will turn yellow, wilt, and eventually die. Similarly, watering the plants too much can also harm them and cause their leaves to turn yellow. Overwatering causes the roots to drown and become susceptible to root rot, which could be fatal if it becomes severe.
Spinach plants should have at least 1 to 1.5 inches of water weekly. Make sure that the surrounding soil is always moist so that the plants stay sufficiently hydrated.
Spinach plants are cool weather crops; excessive heat could harm them and they may turn yellow. Sudden temperature changes from low to high temperatures could also be fatal for the plants. To limit their exposure to warmer temperatures, these plants should be planted early in the spring or during the fall. Provide some shade to keep the plants cool and apply a layer of mulch around the plants.
If you live in a place with a warmer climate, opt for varieties that are heat resistant and tolerant, such as Olympia and Bloomsdale.
When plants are transplanted, they often experience transplant shock due to the sudden change of environment and the light exposure that the roots receive. Since the plants become stressed, they may experience stunted growth and yellowing leaves.
To reduce the effects, allow your plants to develop more before transplanting them. Give the plants at least three to four weeks of growth before eventually transplanting them. You may also use seaweed extract to reduce the impact of transplant shock. This also provides a stronger root system and faster growth.
Spinach leaves turning yellow may also be due to the normal process of aging. Since there is no way to combat aging in plants, you can harvest the outermost leaves first, as these are the oldest and the most likely to turn yellow.
Spinach plants are cold-resistant, but also prone to certain conditions that cause yellowing leaves. This could be due to malnutrition, nutrient deficiencies, diseases such as root rot, Fusarium wilt or downy mildew, or it could be due to temperature changes or transplant shock.
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