Although garlic is usually classified as an herb or spice, the plant is actually a member of the onion family. Garlic plants begin life as a single segment of a round bulb. This segment is known as a clove. The plant sprouts from the clove and eventually forms a new bulb. Gardeners may purchase cloves for planting in a garden center or plant nursery. If your garlic fails to thrive, you can easily determine the problem by examining the plant.
Examine the stems and foliage of garlic. The condition of the stems and foliage may indicate a nutrient deficiency in the soil or a pest problem. For example, if the tips of garlic stems and leaves are yellow, the plant may suffer from nitrogen deficiency while purplish gray fuzz on the stems or leaves may indicate problems with diseases such as downy mildew. Whitish or blotchy specks on leaves can be indicative of onion thrips while yellow or wilted leaves and stems may indicate the presence of onion maggots.
Dig up a garlic plant with a garden trowel.
Examine the bulb of garlic. Many problems that occur while growing garlic leave evidence in the bulb. For example, a misshapen bulb may be a sign that the plant was growing in poor clay soil instead of rich loam. Bulbs with yellow tips are a sign of water stress, nutrient deficiency or disease. Rotten bulbs may be a sign of poor drainage in the soil or a root rotting disease such as fusarium basal rot. If the bulbs are undersized, it can be indicative of parsite insects such as thrips. If the roots contain enlarged nodules which are known as galls, the plant may be infected by root knot nematodes.
Compare your observations of the garlic's symptoms against a gardening reference book (such as the title in References). Gardening references will outline all of the potential problems that a garlic bulb may encounter. Rule out problems that do not show the same symptoms that your garlic exhibits in order to narrow down your assessment.
Transport your garlic bulb to your local agricultural university Extension Service. An agent with the county extension service is extensively trained in agriculture and will be knowledgeable about issues that your garlic may be facing in your region during this time period. The agent can also help you to diagnose your problem by examining the plant.