Why are my garlic leaves turning yellow?

Normal or a problem?

Start with timing and pattern. Garlic leaves die back from the bottom up as the bulbs mature, so yellow and brown lower leaves with green upper leaves, close to harvest, are expected. Yellowing in early to mid spring, while plants should be growing hard, is worth a closer look. Note whether the whole plant is pale, only the tips are yellow, the leaves have spots or streaks, or the plant wobbles when you tug it. Then dig one struggling plant and look at the roots, the base of the bulb and the leaf sheaths, with a hand lens if you have one.

Common spring causes

Pale yellow-green plants with yellow leaf tips and thin stems point to nitrogen deficiency, according to University of Minnesota Extension. Garlic is a heavy feeder, and fall-planted garlic often runs short as growth takes off in spring, especially in sandy soil or after a wet spell. Waterlogged soil does similar harm: roots sitting in water can't take up nutrients, and plants yellow and may start to rot at the base. A hard freeze on tender new spring growth can also brown leaf tips; if the newest leaves come in green, the plant is recovering.

Disease and pests

Garlic rust shows as small, bright orange spots on the leaves and stems, sometimes with black spots at their edges; heavy infection makes leaves yellow and dry, and bulbs stay small. Minnesota also lists rots that start with yellow leaves. Fusarium basal rot yellows leaves from the tip down, with a watery brown decay at the base of the bulb. White rot leaves white, fluffy growth and tiny black specks on a soft bulb. Botrytis neck rot makes the neck look water-soaked at the soil line, mostly in cool, wet weather or heavy soil.

If a yellowing plant pulls up with almost no resistance and few roots, look closely at the base. Bulb mites are tiny, slow, creamy-white mites, 0.02–0.04 inch long, that cluster under the scales and at the root plate. University of Maryland Extension notes they cause general yellowing with brown tips, and the root plate may separate from the bulb. Stem and bulb nematodes leave plants stunted, with short, thick, distorted leaves and a soft neck. Onion maggots cause yellowing and wilting, sometimes fast, with holes in the bulb.

What to do now

For pale, hungry plants in spring, side-dress with compost or a nitrogen fertilizer at the label or soil-test rate, and keep the soil evenly moist at about 1 inch of water a week. Ease off watering about 2 weeks before harvest. Pull and bag plants with rot, mites or nematodes rather than composting them. For light rust, remove the worst leaves and give plants more space for air. If the yellowing is maturity, harvest when the lower third to half of the leaves have browned, then cure in a dry, airy spot out of direct sun for at least 10–14 days, often 3–4 weeks, until the necks are tight.

Next season

Next fall, plant in well-drained soil or a raised bed, in a spot where no garlic or onions have grown for several years. Buy certified, disease-free seed garlic rather than grocery-store bulbs, and don't replant cloves from a crop that had mites or rot. Maryland notes that soaking seed cloves in 130°F water for 10–20 minutes can reduce bulb mites, though it also lowers sprouting. Work compost in before planting, and plan to feed again as spring growth starts.