Hot weather and frequent watering can deplete essential nutrients from the soil, causing garlic and onion leaves to yellow; proper fertilization and pest control are crucial for a successful harvest.

Agronomists recommend adjusting fertilization strategies in June due to heat-related challenges affecting garlic and onion crops. The primary fertilization usually occurs during planting and in May, but high temperatures necessitate more frequent watering, which can leach nitrogen from the soil, impacting bulb development.

To counteract this, farmers should apply nitrogen-based fertilizers in small, diluted doses, reducing the amount specified on the product packaging to avoid over-fertilization. Alternatively, a fermented grass infusion can be used as a natural fertilizer. This involves soaking chopped grass (excluding herbicide-treated grass) in water with a tablespoon of urea for about a week until fermentation occurs. The resulting dark green liquid should be diluted before application after the main watering, preferably in the evening or early morning.

Yellowing leaves can also indicate pest infestation, particularly by the onion fly. This pest damages the bulb, causing the plant to deteriorate quickly. To check for onion flies, examine the bulbs for tunnels and remove any infested plants from the garden. Several methods can control onion flies, including crop rotation (avoiding planting onions in the same spot consecutively or near leeks and tulips, while carrots can be beneficial neighbors). Dusting the beds regularly with ash or a mixture of tobacco dust and ash can deter the flies. Additionally, a solution of ammonia water (one glass in 10 liters of water) applied every 7-10 days after watering can help.

Proper watering practices are vital for onion and garlic health. Onions are sensitive to fluctuating humidity, so consistent and abundant watering once a week is recommended, ensuring the soil is thoroughly soaked. Loosening the soil after watering and mulching can help retain moisture, prevent weed growth, and improve oxygenation.