Why are my garlic leaves going yellow?

Garlic goes yellow twice: once as a signal that it is ready, and once as a symptom. The difference is timing and direction. Getting that distinction right decides whether you lift a good crop or spend the summer worrying about a plant that was finishing normally.

Step by step

1. Check the date and how much of the plant is affected.From late spring into early summer, lower leaves yellowing and dying back progressively is ripening. That is the crop telling you harvest is approaching. Leave it alone.
2. In spring, look at where the yellowing starts.Tips going yellow and browning first is usually cold, wind or a nutrient shortage. Whole leaves yellowing from the base upwards, with the plant looking limp, suggests a root problem.
3. Pull one suspect plant and look at the base.This is the decisive check. Healthy roots are white and numerous. If the base plate is rotting, the roots have gone and there is a white fluffy mould with tiny black specks in it, that is white rot.
4. Understand what white rot means.There is no treatment. The resting bodies survive in soil for fifteen to twenty years and are activated by anything in the onion family. Do not grow alliums on that ground again, remove and bin the affected plants, and be careful not to move soil on boots or tools.
5. Rule out waterlogging.Garlic in wet winter soil yellows, stunts and rots. On heavy ground, plant into raised ridges or beds. If the row sits in standing water after rain, that is the problem.
6. Consider nitrogen.Uniform pale yellowing across the whole plant in early spring, with slow growth, usually means hunger — garlic grows through the coldest, wettest months when nitrogen leaches. A nitrogen-rich feed in late winter and early spring corrects it.
7. Look for orange streaks rather than plain yellow.Bright orange raised pustules on the leaves are allium rust, a different problem with a different answer.
8. Check for frost and wind damage.Tip scorch and yellow-white streaking after a hard frost or a cold drying wind looks alarming and is usually cosmetic. The plant grows out of it.

Tips

• Buy planting stock from a supplier rather than replanting from a crop that showed any base rot — white rot travels on cloves.
• Yellowing on a spring-planted crop is more common simply because the plant is under more pressure in a shorter season.
• Garlic in containers yellows readily once the compost runs out of nitrogen, usually around March. Feed it.
• Do not add lime specifically for garlic. It likes a near-neutral soil but liming a bed to correct yellowing is treating the wrong thing.

Common mistakes

• Watering more when leaves yellow in summer — It is ripening. Extra water at that point softens the neck and ruins storage life.
• Composting white-rot-affected plants — The resting bodies survive and you spread the problem across the whole garden with the compost.
• Treating every yellow leaf as a disease — Garlic yellows as part of its normal cycle. Reading the season first prevents a lot of unnecessary intervention.

If it doesn't work

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