Garlic, like many crops, likes rich, well drained, friable soil with plenty of organic matter and a ph between 6.5 and 7. Soil content can greatly affect garlic; for example, sulfur rich soil will produce more pungent garlic, while iron levels will influence coloration. Work beds deeply and incorporate compost or aged manure. It is necessary to rotate garlic and all other alliums at a minimum of a three year basis so as to prevent disease and build healthy soil.
Garlic is best planted in the fall, a month or so before the ground freezes. In the north, this is usually in October. In milder climates later planting is possible. Here, garlic is planted in November. Carefully break bulbs into individual cloves within a few days of planting as this signals the beginning of growth. Be careful not to break the root base, called the “basal plate” when separating cloves. Damaged cloves are susceptible to infection and rot. Select the largest cloves for planting as these will yield the largest heads. When importing new allium plant material into your soil, a minor precaution against pests and fungi is to soak cloves in isopropyl alcohol (regular strength is sufficient) for 10 minutes and let completely dry out before planting, or alternatively soak for 10 minutes in a 10% bleach solution with a drop or two of dish soap (as a surfactant), then dunk/soak in hot, 110° F water to rinse, just prior to planting. See below for further discussion. Plant cloves basal plate downwards, tips up. An inch deep planting is sufficient for most areas, but where winters are severe, planting up to 3” is recommended. Spacing varies with every grower. Factors contributing towards yield include soil fertility, competition for light, and ease of cultivation. For raised beds with two foot depth, garlic can be planted on 6” centers. For row planting, garlic spaced 5-8” apart in rows 8-10” apart, is adequate. It is helpful to cluster varieties that you expect to harvest around the same time.
Garlic does not handle competition from weeds. For a good harvest it is crucial to stay ahead on weeding. Mulch is useful for suppressing weed growth, though it often contains weed seed itself. It also helps regulate fluctuations in soil temperature, preventing evaporation and soil compaction from rain and heaving from freezing. On the other hand, mulch can slow down the warming of the soil in the spring. I have encountered cool damp spells near harvest time and found it necessary to remove the mulch to aid in drying the soil. Mulch material is varied; i have heard of successful use of shredded leaves, lawn grass clippings, even plastic. I put 4-6 inches of clean straw or spoiled alfalfa down immediately after planting. While most shoots will punch through the mulch, a few plants will inevitably need assistance.
Many growers fertilize with nitrogen after spring emergence to promote healthy leaf growth. Some side dress with composted manures or alfalfa meal, others water in fertilizers. Foliar feeding with a combo of wettable fish and seaweed concentrates is another option. While garlic’s waxy leaves limit absorption of foliar fertilizers, using a surfactant, a drop or so of dish soap per gallon, will decrease the surface tension of the water, thus increase its ability to spread, wet and penetrate the leaves. It is best to foliar feed early in the morning or evening to maximize absorption time. As the days lengthen and get hot, leaf growth slows and stops. At this point, fertilization will not increase plant growth as it is transitioning into a bulb, trying to reproduce before going into dormancy.
Water in the spring as with any leafy garden vegetable. Adequate moisture is important during bulb development; water and soil fertility are major determining factors in bulb size. Garlic enjoys soil that is moist but not sodden. Green leaves correspond with living bulb wrappers and the dead bottom leaves correspond with dead bulb wrappers. Moisture on this necrotic tissue can cause infection so good drainage is beneficial in this regard. Reduce and cut off water a week prior to harvest. As garlic varieties mature at different times, positioning of garlic types in respect to irrigation is best determined at planting time. If the soil is too wet as harvest approaches, removal of mulch may be necessary, albeit tedious.
Hardneck garlics send up flower stems known as scapes. Removal of the scapes redirects the plant’s energy from trying (and failing) to reproduce sexually, into bulb formation and success in clonal reproduction. Growers differ on when it’s best to remove them. Some snip them shortly after emergence, others recommend waiting until after they uncoil, citing evidence of increased storage capacity when cut at this stage. I harvest when they are large enough to be optimal as a vegetable, usually when the scapes are in coil, but before they get tough and fibrous. Snip the scape just above the top leaf on a dry sunny day. Yum.
Garlic is generally harvested in the summer. In the north, this can be as late as August and the harvest window will be narrower. Here in SW Oregon, my harvest generally begins at the end of May for very early varieties and continues to mid July for late ones. Cold springs make for later harvests. The lower leaves will begin to dry down as the plant nears maturity. I generally harvest when there are 4-6 semi-green leaves remaining on any given variety; however, this is only a guideline. Pulling a few plants and checking them out to see if the cloves are well formed with good wrappers is best before committing to a major harvest. Pop the plants up in the soil using a fork or spade, being careful not to cut or bruise the bulbs and brush off soil from around the roots. Exposure to direct sunlight for more than a few minutes may scald the cloves. Covering harvested plants with a sheet can help and prompt removal of plants to a curing shed is beneficial. Occasionally i will harvest a plant with the scape still intact or even just emerging. When left on, these will not only take longer to cure but the scapes will continue to develop, diverting energy from the bulb so it’s worth severing these.
Garlic can be cured in a shed, garage or any well ventilated space out of direct sunlight. Hang plants in bundles of ten or more depending on size; alternatively, lay out on racks or screens in a single layer. Air circulation between bulbs is very important. As the bulbs cure garlic will lose as much as 20% of its weight to evaporation and that moisture needs a place to go. Curing can take from three to six weeks. Multi-layered softnecks take longer than the single layered hardnecks. Curing enables good storage and concentrates the garlic’s flavor. After curing, cut tops and roots half an inch above and below the bulb and gently brush or rub off dirt. It’s worth noting that most garlic will store better if the tops are left on as moisture will transpire through the neck.
Stored garlic needs good air circulation. After cleaning store in mesh sacks, braids or bundles. Most varieties do well with around 60% humidity. Softnecks are generally more tolerant of varying humidity levels. Hardnecks are fussier. Rocambole, Glazed and Marbled garlics tend to dehydrate at low humidity levels. Purple Stripes and many other hardnecks will swell on the root nodules when the humidity gets over 70%. Temperatures between around 50 and 60 degrees are optimal. Consistent temperature and humidity levels also facilitate longer storage.
Diseases & Pests
In spite of its medicinal qualities such as being anti-microbial, antibiotic, anti-fungal, etc, while growing, garlic is actually susceptible to a number pests and diseases. If you encounter problems, the best way to diagnose is to send a sample to a lab; however there are a couple of web sites which are very helpful in disease and pest diagnostics:
Oregon State University: http://plant-clinic.bpp.oregonstate.edu/garlic
UC Davis: http://www.ipm.ucdavis.edu/PMG/selectnewpest.onion-and-garlic.html
For those farming garlic or onions, the book The Compendium of Onion and Garlic Diseases and Pests is a valuable resource for diagnosis and analysis of problems.
Ultimately, prevention is the best course. We handle garlic numerous times from selection of planting stock, clove popping, planting, scape removal, harvest, hanging, cleaning, packing bulbs for shipment. All bulbs are carefully inspected for quality while being packed for shipment but really, we look for health or weakness at every interaction. While i am unconvinced of the efficacy of foliar feeding given how waxy garlic leaves are but it is by design an opportunity to inspect every single plant and inevitably some need help breaking through the mulch, others get rouged out. No matter what steps are taken here, like most garlic growers i have experienced various problems over the years. There are two issues garlic growers often contend with, the first is easily diagnosable: fusarium. The second is far more common but most growers are unaware of: bulb mites. I have received garlic samples from different regions of the continental U.S. and found these little buggers frolicking beneath the scales of cloves. They are hard to identify, even with a hand lens but they can be seen at 90x magnification nibbling away at the flesh and the film between the clove and peel. This will accelerate desiccation and leave bulbs open for other diseases when planted, including pathogenic fungi. Problematically, mite presence is undetectable until well into storage. Not enough is known about the life cycle of the dry bulb mite, Aceria tulipae and more research needs to be done to form effective management strategies but there are pre-plant treatment that kill mites. One is an overnight soak in a solution of water with 2% mineral oil and 2% dish soap as a surfactant. This suffocates the mites. Here at Garlicana, a 10% bleach solution with a dollop of dish soap is used. Neither isopropyl alcohol nor agricultural hydrogen peroxide with acetic acid (products like Jet-Ag and Oxidate) are effective as they must come into contact with the mites which linger beneath the film. The chlorine has a fumagative effect which penetrates the film. Hot water treatment also shows efficacy on mites as well as other pathogens. See above links for further information. As mites are in the soil, effective mite kill on planting stock, doesn’t guarantee that you will have miteless garlic. Again, further study is necessary to understand the life cycle but for now, preventative treatment remains the best option and here we have seen great improvements in recent years.