Why Are the Edges of My Zucchini Leaves Turning Brown?

When browning on a zucchini leaf begins at the outer margins and dries inward, leaving the rim crisp while the centre stays green, you are nearly always looking at a moisture or feeding issue rather than a disease. Diseases tend to make spots and patches across the leaf; scorched edges point to the plant struggling to keep its leaf margins supplied with water and nutrients. Let me run through the causes and how to tell them apart.

Drought and inconsistent watering

The leaf edge is the furthest point from the veins, so it is the first place to dry out when water runs short. A zucchini with large, thirsty leaves browns at the margins when the soil dries or watering is erratic, and this happens fast in heat and in containers. Check the soil a couple of inches down; if it is dry, the plant needs deeper, more consistent watering. Mulch heavily to hold moisture and even out the supply. Because zucchini transpire so much through their big leaves, they are quick to scorch when thirsty, so steady watering is the first fix to try.

Fertiliser burn

The opposite problem produces a similar look. Over-feeding, or a build-up of fertiliser salts in the soil, pulls water back out of the roots and scorches the leaf margins brown and crispy while the centres stay green. A white crusty residue on the soil surface is a clue. If you have been feeding heavily — easy to do with hungry zucchini — flush the soil by watering slowly and deeply to leach the excess salts past the roots, then pause feeding for a few weeks and always feed at the recommended strength.

Potassium shortage

A specific nutrient deficiency mimics drought scorch closely. Zucchini use a lot of potassium, especially once they begin their heavy fruiting, and a potassium shortage shows as scorched, browning margins on the older leaves while the veins and centres stay green, often with disappointing fruit alongside. If your plant is cropping hard and the older leaves are crisping at the edges, a potassium-rich tomato or fruiting feed often corrects it. This is easy to mistake for simple drought, so consider your feeding as well as your watering.

Wind, sun and transplant shock

A few environmental factors crisp the edges too. Hot, dry wind dries leaf margins directly, especially on exposed plants. Strong sun on a plant that was not hardened off can scorch the most exposed leaf edges. And a freshly transplanted zucchini, whose roots have not yet established, may brown at the margins from the stress of the move until it settles. These are usually temporary once the plant adapts or the weather eases.

Pinning down the cause

Read the pattern: crispy margins in dry soil or heat equals drought — water deeper and mulch; scorched edges with a salty crust after heavy feeding equals fertiliser burn — flush and ease off; browning margins on older leaves of a heavily fruiting plant equals potassium shortage — feed potassium; edges browning on a windy, exposed or newly moved plant equals environmental stress — shelter and wait. None of these are diseases, so the fixes are about water, feed and shelter, not sprays.