Garlic Harvest, Curing, and Storage

Garlic harvest is a big, landmark summer task that usually occurs around mid- to late July. As you start to prepare for garlic harvest, here are some tips from Crystal Stewart-Courtens of Cornell Cooperative Extension on determining ideal harvest timing: heads should be left in the ground as long as possible to attain maximum bulb size (which doubles in the last stage of growth), but not so long that the cloves begin to separate, as overripe bulbs sell and store poorly. Harvest when leaves begin to turn yellow, but when about 60% are still green—one rule of thumb is to harvest when there are a minimum of three leaves left that have not begun to brown at the tips. Check bulbs by cutting through the head sideways to see if the cloves fill the wrappers – if they are loose within the wrappers, the garlic has a little ways to grow. A little of the outermost wrapper may have started to discolor at this point. Harvest before the cloves start to separate from each other within the bulb, which can happen relatively quickly, especially in a wet year. It is better to harvest too early than too late.

Use hand tools to loosen soil under the bulbs or a mechanical harvester to undercut the bed. Pulling bulbs out when they are tight in the ground can open wounds at the stem-bulb junction and allow for fungal infections. Fresh bulbs bruise easily and these wounds can also encourage infection. Don’t knock off dirt by banging bulbs against each other, boots, shovels, or buckets— shake or rub gently, and leave the rest to dry out during curing. 

If short on curing space, tops can be cut in the field, with a sickle bar mower or by hand, leaving stems as short as 1.5” or as high as 6”. In many cases, topping vs. not is dictated by curing scenarios—leaving tops on can facilitate hanging bulbs to cure, whereas topping plants is more conducive to curing in bulb crates or mesh bags. Recent Cornell trials have indicated that disease incidence does not increase when trimming garlic down at this stage.

Curing is important for successful bulb storage and finding the ideal conditions for curing can be a challenge. Curing in the field runs the risk of sunscald, while curing in poorly ventilated barns can result in yield loss from disease. Good airflow around the bulbs is critical. Avoid high temperatures (above 90°F) and bright sunlight. Stewart-Courtens notes that garlic will dry well even at 110°F but a physiological disorder called waxy breakdown starts to occur at about 120°F, so be sure to monitor temperatures in the drying area. Rapid curing can be achieved by placing trimmed bulbs roots-up on 1” wire mesh in a hoophouse or high tunnel covered with shade cloth, and with the sides and ends open. A well-ventilated barn will also work, but be sure that bulbs are hung with adequate air circulation or on open racks up off the floor. Curing takes 10 to 14 days and is complete when the outer skins are dry and crispy, the neck is constricted, and the center of the cut stem is hard. 

Storing Bulbs. After curing, garlic can be kept in good condition for 1 to 2 months at ambient temperatures of 68 to 86°F under low relative humidity (< 75%). However, under these warm conditions, bulbs will eventually become soft, spongy and shriveled due to water loss. For long-term storage, garlic is best maintained at temperatures of 30 to 32°F with low relative humidity (60 to 70%). Good airflow throughout storage containers is necessary to prevent any moisture accumulation. Under these conditions, well-cured garlic can be stored for 6 to 7 months. Storage at higher temperatures (60°F) may be adequate for the short term, but it is important to select a place with low relative humidity and good air flow. As with onions, relative humidity needs to be lower than for most vegetables because high humidity causes root and mold growth; on the other hand, if it is too dry, the bulbs will dry out. 

Storing Seed. Garlic bulbs that are to be used as seed for fall planting of next years’ crop should be stored at 50°F and at relative humidity of 65 to 70%. Garlic cloves break dormancy most rapidly between 40 to 50°F, hence prolonged storage at this temperature range should be avoided. Storage of planting stock at temperatures below 40°F results in rough bulbs, side-shoot sprouting (witch’s brooms) and early maturity, while storage above 65°F results in delayed sprouting and late maturity.

Garlic cloves used for seed should be of the highest quality, with no disease infections, as these can be spread to new fields and to the next year’s crop. See our Culling Garlic: Don’t Store or Plant Infected Bulbs article for what diseases and pests to look out for when preparing seed garlic. One of the most important clove-borne pests of garlic is garlic bloat nematode—keep an eye out for symptoms of this devastating pest and submit samples to the UMass Plant Disease Diagnostic Lab to make a positive identification; for submission instructions and contact info visit https://ag.umass.edu/services/plant-diagnostics-laboratory.

Over 2019 and 2020, Christy Hoepting of Cornell Cooperative Extension, conducted trials to evaluate various garlic curing and storage conditions. A planting of German hardneck garlic was divided up between 13 and 24 storage regimes in 2019 and 2020, respectively, and bulb characteristics including % shrink, bulb density, bulb firmness, wrapper tightness, bulb color, and Fusarium and black mold incidence were evaluated. Here are some take-home messages from the trials:

• The best-performing treatment was curing in a greenhouse with open sides, no fans, with garlic in mesh bags in a single layer on wooden pallets. After curing, the garlic was stored in a steel barn, where temperatures never dropped below 50°F and relative humidity ranged from 50-80%.
• Warm and humid storage conditions resulted in high incidence of Fusarium bulb rot, as would be expected.
• Cold storage reduced the incidence of Eriophyid mites, as lower temperatures inhibit their reproduction. E. mite populations will grow at room temperature.
• No consistent trends were observed in regards to topping vs. not topping. Neither practice led to higher rates of disease incidence or consistent differences in bulb quality. However, it does take longer to cure garlic with tops on (see Table 2).
• Washing or rainfall during curing reduced bulb quality and increased disease.
• Curing garlic in 1-ton boxes with heated forced air reduced bulb quality.

A useful summary from Hoepting’s write-up:

No matter the post-harvest practices used by our growers, the garlic came back fairly high quality. If you are happy with the quality of your garlic, do not change a thing. If your garlic has softer bulbs and looser wrapper leaves than you would like, consider adjusting your curing or storage conditions. Perhaps, it is being kept in the curing phase for too long and is being overdried. Maybe, you can cure it slower with natural ventilation instead of with fans, or top the bulbs to leave a longer neck (e.g. 6”). If you have issues with eryophyid mites showing up after storage, consider storing your garlic under cooler conditions. In very general terms, high humidity (>85%) for prolonged periods of time, no matter the temperature, can exacerbate diseases.