By Azura · Updated June 2026 · Raised Garden Hub is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no extra cost to you.
Yellow zucchini leaves are a symptom, not a death sentence. Work through these eight causes from most to least common and you’ll usually spot it fast.
1. Overwatering (the #1 culprit)
Soggy soil starves roots of oxygen, turning lower leaves yellow. Fix: let the top inch dry between waterings; make sure the bed drains freely.
2. Nitrogen deficiency
Older leaves yellow first, from the tips inward. Fix: feed with a balanced or nitrogen-rich fertilizer; top-dress with compost.
3. Magnesium or iron deficiency
Yellowing between the veins (veins stay green) points to magnesium (older leaves) or iron (new leaves). Fix: for magnesium, a dose of Epsom salts — but only if a soil test confirms the deficiency, since adding it to already-adequate soil can block calcium uptake. Check soil pH for iron lockout.
4. Powdery mildew
A white dusting that precedes yellowing. Fix: improve airflow, water at the base, and treat with a milk or potassium-bicarbonate spray.
5. Squash bugs / vine borers
Pests sucking sap cause patchy yellowing and wilting. Fix: check leaf undersides for eggs; remove by hand; use row covers early in the season.
6. Too much sun stress / heat
In extreme heat leaves can yellow and scorch. Fix: mulch to keep roots cool and water in the morning.
7. pH out of range
Zucchini likes a pH around 6.0–7.0. Outside that, nutrients lock out. Fix: test and amend.
8. Natural aging
The oldest, lowest leaves yellowing slowly while the plant thrives is normal. Fix: nothing — just remove them.
Prevention in raised beds
Most yellowing traces back to soil and water. A free-draining soil mix and consistent (not constant) watering prevent the majority of cases. The same logic applies to cucumbers, squash, and pumpkins.