7 Reasons Why Your Young Zucchini Plant Has Yellow Leaves, Plus How to Fix It Fast

• Leaves on a young zucchini plant could be turning yellow because of under or overwatering.
• It could also be fertilizer burn, pests, diseases, transplant shock, low nutrition, or just a result of aging.
• Check and test your plant constantly in order to monitor its progress as you make appropriate adjustments.

Zucchini, or summer squash, is one of the easiest vegetables to grow. When the leaves of your plant turn yellow, it is certainly concerning, but your zucchini isn’t doomed. In most cases, the issue can be fixed with a few easy steps.

Find out why your young zucchini leaves are turning yellow, what to do about it, and how to prevent it from happening again.

Why Zucchini Leaves are Turning Yellow 

Just because your young zucchini has yellow leaves doesn’t mean it’s all over. Here are eight reasons why this might be happening to your plant.

Too Little or Too Much Water

Zucchini plants need at least 1 inch of water per week, and a little more in hot weather. Zucchini in containers require more frequent watering.

Overwatering doesn’t only happens when you water your plants too much, but also with moderate amounts of water and poorly drained soil; the roots gets waterlogged and are unable to take up nutrients, leading to yellow leaves.

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Lack of Nutrients

Insufficient nitrogen, iron, and magnesium in the soil may turn zucchini leaves yellow. If the only the bottom leaves are yellow and the top leaves are still slightly greener, the culprit is likely nitrogen deficiency; nitrogen is mobile in the plant and when there is a shortage it moves from the old growth to the new growth.

Fertilizer Burn

The cause of fertilizer burn can be either too much fertilizer in the soil or fertilizer that was applied to wet foliage. The excess salts in the fertilizer draw moisture from the plants, causing the leaves to yellow, brown, or dry out. 

Transplant Shock

Zucchini has tender roots that are prone to transplant shock. Often, older leaves turn yellow and drop off after transplanting while the plant puts its energy into growing more roots and new leaves.

Pests

Aphids suck the saps out of zucchini leaves so they turn yellow and curl. Squash bugs also extract the sap from zucchini leaves, causing yellow or brown spots and wilting. 

Spider mites, which are difficult to see with the naked eye, appear mostly in dry conditions and cause speckled or mottled leaves that later turn yellow.

Diseases

Powdery mildew on leaves starts as white and may turn yellow and brown later. It is an unsightly fungal disease, but it is not deadly. Verticillium wilt is an incurable soil-borne fungal disease that causes wilting, yellowing, and eventually kills the plant. 

Natural Aging

Especially later in the season, older leaves turn yellow leaves, which is part so the plant’s natural aging process and nothing to worry about.

How to Treat a Zucchini With Yellow Leaves 

• Transplant shock: This fixes itself. During that time, make sure the plant is well-watered to prevent further drought stress.
• Watering: If improper watering caused the yellow leaves, adjust your watering practice. Be sure to feel the soil dampness consistently, and definitely before watering.
• Nutrients: In the case of nutrient deficiency, feed your zucchini with a quick-acting liquid fertilizer that is high in nitrogen, such as fish emulsion.
• Fertilizer burn: To remedy fertilizer burn, flush the soil with water to dilute the excess nutrients and remove any damaged leaves.
• Pests: Pests can often be removed with a strong blast of water. If they persist, apply insecticidal soap or another organic pesticide labeled for edibles.
• Powdery mildew: To control the early stages of powdery mildew, remove and discard affected leaves or try applying homemade fungicides like vinegar, milk, or baking soda.
• Verticillium: A zucchini plant infected with verticillium wilt is unfortunately beyond hope, and you should remove it immediately from your garden.

How to Keep Zucchini Leaves From Turning Yellow 

• Harden off seedlings fully before transplanting them outdoors. Plant on an overcast day and—during the first few days—shade young plants and protect them from strong winds.
• Do not plant in a spot where you have grown other members of the cucumber family in the past two years, preferably longer. Practicing crop rotation is key to healthy plants because some pests and pathogens, such as verticillium wilt, survive in the soil for many years.
• Make sure the growing conditions are right. The soil should be well-draining and amended with plenty of organic matter, with a pH between 6.0 and 7.0. If unsure, test the soil pH because improper pH affects nutrient uptake.
• Give zucchini a location in full sun where they receive at least 6, better 8 hours of direct sunlight every day.
• Water and fertilize just the right amount, and apply mulch to conserve soil moisture. 
• Keep an eye out for pests and diseases so you can treat them promptly; the earlier you catch issues, the better.

Good Zucchini Companion Plants 

• Beans and peas are legumes that release nitrogen to the soil, which benefits zucchini plants. 
• Corn provides shade, which is especially welcome in a hot climate during the afternoon. The corn stalks also offer vine-type zucchini plants support for climbing. 
• Radishes make excellent zucchini companion plants because they deter squash vine borers. 
• Nasturtiums serve as a trap crop for aphids and attract pollinating insects. 
• Marigolds, in addition to luring aphids and other pests away from zucchini plants, kill soil nematodes, destructive soil-dwelling worms, by releasing a chemical in the soil.
• Dill repels aphids and spider mites. Its flowers attract beneficial insects such as hoverflies and ladybugs, which prey on aphids. 
• Borage is a pollinator magnet, ensuring a good zucchini crop.