Garlic grows best in well-drained soil with a high pH and concentration of organic matter. Soil must be tilled prior to planting to provide a loose growing bed for bulb development.
Cloves are planted an inch deep in the fall or early spring, with the pointed side up. Garlic is sometimes sprayed with sprout inhibitors during preharvest to help control development and lengthen the storage period.
Pests & Diseases
Leafminers are small black and yellow flies that damage garlic by feeding on plant sap and laying eggs within leaf tissue. The larvae then tunnel within the tissue and may also hollow out the bulb. Damage is not a concern unless populations are so high they prematurely kill foliage. Natural enemies like wasps can reduce infestation. Bulb mites are shiny, white pests that appear in clusters on damaged areas under the root of the garlic bulb, stunt growth, and contribute to rot in stored garlic. They are most damaging during cool, wet weather.
A common disease seen in garlic is penicillium rot, characterized by lightweight bulbs and soft or spongy cloves. As the decay advances, cloves break down into a grey powdery mass. Storage in low humidity will help prevent this type of decay. Other types of rot include basal rot, which attacks plants already weakened by other diseases or insects and causes yellowing and dieback of leaves, along with white fungal growth at the bulb base. White rot causes white, fluffy fungal growth and small, dark sclerotia, and kills faster than basal rot.
Downy mildew can survive for years in the soil, kills younger plants, and stunts the growth of older plants. Symptoms include whitish, furry growth on leaves, yellow discoloration, and blackened, shriveled necks with water-soaked scales on stored bulbs. Waxy breakdown is a physiological disorder affecting the later stages of growth and associated with periods of high temperature near harvest time. Low levels of oxygen and inadequate ventilation may also contribute. This disorder is rarely seen in the field and generally found in stored or shipped garlic.
Storage & Packaging
Garlic can be harvested at different times for specialty markets, but is generally harvested after the tops have fallen and are very dry. Bulbs should be dug up with roots and shoots attached, tied in groups of 10 to 15, and dried in a well-ventilated room. Because damage can occur during mechanical harvest, garlic is often harvested by hand, especially for sales to the fresh market. High carbon dioxide and temperatures between 30 and 32°F are beneficial during storage. It is best to keep relative humidity to between 60 and 70%. Freezing injury can occur at temperatures below 30°F.
References: Cornell University, Iowa State University Extension, University of California Agriculture & Natural Resources, University of Minnesota Extension.