Why Are My Squash Leaves Turning Yellow

If you’re a gardener, seeing yellow leaves on your squash plants is a common worry. This article explains why are my squash leaves turning yellow and how to fix it. Don’t panic—yellow leaves are a plant’s way of telling you something is off. The good news is that many causes are simple to correct once you know what to look for.

We’ll walk through the most frequent reasons, from watering issues to pests. You’ll learn how to diagnose the problem and take action to get your plants back to health. With some attention, your squash can recover and produce a great harvest.

Yellowing leaves, called chlorosis, means the green pigment chlorophyll is breaking down. This happens for many reasons. Identifying the specific pattern and location of the yellowing is your first clue. Let’s break down the possibilities.

Watering Problems: Too Much or Too Little

Incorrect watering is the top culprit for yellow squash leaves. Both overwatering and underwatering stress the plant.

Overwatering: Soggy soil suffocates roots. They can’t breathe or take up nutrients. Leaves turn yellow, often starting with the older ones. The plant may look wilted even though the soil is wet.
Underwatering: Without enough water, plants can’t transport nutrients. Leaves turn yellow, become dry and crispy, and may curl. The soil will pull away from the edges of the container or feel dry deep down.

The Fix: Check soil moisture before watering. Stick your finger 2-3 inches into the soil. Water deeply only when it feels dry at that depth. Ensure your soil or container drains well.

Nutrient Deficiencies: What’s Missing?

Plants need a balanced diet. Key deficiencies cause distinct yellowing patterns.

Nitrogen Deficiency: The most common. Older, lower leaves turn uniformly yellow. The plant redirects nitrogen to new growth. This can stunt overall growth.
Iron Deficiency: New leaves turn yellow between the veins, which stay green. Often occurs in soil that is too alkaline.
Magnesium Deficiency: Older leaves yellow in a mosaic pattern, with veins maybe staying green. It can look similar to some diseases.

The Fix: For a quick nitrogen boost, use a balanced, water-soluble fertilizer. For long-term soil health, mix in compost at planting. A soil test is the best way to know exactly what your soil lacks.

Pests That Suck the Life Out of Leaves

Sap-sucking insects drain nutrients directly, causing yellow speckles or patches.

Squash Bugs: These flat, grayish-brown bugs cluster on stems and undersides of leaves. They cause yellow speckles that eventually turn brown and brittle.
Spider Mites: Tiny pests that create fine webbing. They cause stippling—tiny yellow dots all over the leaf. Leaves may look dusty.
Aphids: Small, soft-bodied insects in green, black, or red. They crowd on new growth and leaf undersides, causing curling and yellowing.

The Fix: Check leaf undersides regularly. Blast pests off with a strong jet of water. For severe infestations, use insecticidal soap or neem oil, applying it directly to the pests.

Diseases That Cause Yellowing

Fungal, bacterial, and viral diseases are a serious cause of yellow leaves.

Powdery Mildew: Starts as white, powdery spots on leaves, which then yellow and wither. It’s very common in late summer.
Fusarium Wilt: A soil-borne fungus. It clogs the vascular system. Leaves yellow on one side of the plant or one vine before wilting completely.
Cucumber Mosaic Virus: Causes a distinctive yellow mottling or mosaic pattern. Leaves become distorted and stunted. There is no cure.

The Fix: For fungal issues like mildew, improve air circulation and avoid wetting leaves. Apply a fungicide labeled for edibles. Remove and destroy severely diseased plants to prevent spread, especially those with viruses.

Environmental and Other Factors

Sometimes, the issue isn’t a bug or disease but the growing conditions.

Natural Aging: It’s normal for the oldest leaves at the base of the plant to yellow and die off as the plant matures. No action needed.
Poor Pollination: If fruits start to grow but then rot, the plant may abort them, sometimes causing stress and yellowing. Hand-pollinate to ensure success.
Root Damage: Cultivating too closely can damage shallow roots, or animals can disturb them. Damaged roots can’t support the foliage.

Step-by-Step Diagnostic Guide

Follow these steps to figure out your plants problem.

Look at the Pattern: Is yellowing on old or new leaves? Is it uniform, veinal, or spotty?
Check the Undersides: Inspect for pests, eggs, or webbing. Use a magnifying glass if needed.
Feel the Soil: Is it sopping wet, bone dry, or just right? Check drainage.
Examine the Whole Plant: Is only one stem affected (hinting at disease or damage) or the entire plant (hinting at water or nutrients)?
Consider the Weather: Has it been extremely wet, dry, or cold lately?

Treatment and Prevention Plan

Once you’ve identified the likely cause, take these corrective actions.

Immediate Actions

Adjust your watering schedule immediately based on your soil check.
Remove severely yellowed or infested leaves and dispose of them in the trash (not compost).
Apply appropriate treatment (like insecticidal soap for bugs or fertilizer for deficiency).

Long-Term Prevention

Water Wisely: Use drip irrigation or soaker hoses to keep leaves dry and deliver water to roots.
Feed Regularly: Squash are heavy feeders. Side-dress with compost or a balanced organic fertilizer when vines start to run and again when flowers appear.
Practice Crop Rotation: Don’t plant squash in the same spot more than once every 3 years to reduce soil-borne disease.
Choose Resistant Varieties: Look for varieties marked with disease resistance codes (like PM for powdery mildew).
Keep it Clean: Remove plant debris at the end of the season to eliminate overwintering sites for pests and diseases.

FAQ: Squash Leaves Turning Yellow

Should I cut off yellow squash leaves?

Yes, but with discretion. Remove leaves that are more than 50% yellow, are diseased, or are heavily infested with pests. This helps the plant focus energy on healthy growth and improves air circulation. Use clean shears and don’t remove to many leaves at once.

Can yellow leaves turn green again?

Once a leaf turns yellow, it will rarely, if ever, regain its green color. The chlorophyll is gone. The goal is to correct the problem so that new growth comes in green and healthy. The plant may eventually shed the yellow leaves itself.

What is the best fertilizer for yellow squash leaves?

A balanced, all-purpose vegetable garden fertilizer (like a 10-10-10 or 5-5-5) is a good start if you suspect a general nutrient issue. If a soil test indicates a specific deficiency, target that. In most cases, compost is an excellent all-around soil amendment that improves nutrient availability.

Is Epsom salt good for yellow squash leaves?

Epsom salt provides magnesium. It can help if your yellowing is truly due to a magnesium deficiency (older leaves with yellowing between veins). However, if the problem is something else, like overwatering or a nitrogen deficiency, it won’t help. Don’t use it as a cure-all without diagnosis.

Why are my squash leaves turning yellow and brown?

Yellow leaves that progress to brown, crispy areas usually indicate a problem that has advanced. This could be severe underwatering, a bad pest infestation (like squash bug damage), or a fungal disease like advanced blight. The browning means the leaf tissue is dying.

Seeing yellow leaves on your squash can be alarming, but it’s a solvable puzzle. Start by checking your watering habits and looking closely for pests. Most often, the issue is something you can manage with a simple adjustment. By observing your plants regularly and acting quickly, you can adress the cause and help your squash plants thrive for a productive season. Remember, gardening is a learning process, and every problem makes you a more observant grower.