Greenhouses can be used in two ways when it comes to garlic. You can grow garlic in your greenhouse or you can dry and cure your garlic in the greenhouse during the summer.
Cultivated garlic, Allium sativum, is a member of the lily family. It may generally be divided into two subspecies: ophioscorodon (hardneck or topset garlic) and sativum (softneck or artichoke garlic). The former produces elongated flower stalks (technically called scapes) and bulbils at the top of the stalk. Soft-neck garlic does not produce bulbils, except in times of stress. It invests its energy instead into the production of larger bulbs and more cloves per bulb. While both bulbils and underground cloves can be replanted, bulbils will take longer— up to two seasons—to produce mature bulbs, and will require special care because the young plants are very small.
Hardneck types like rocambole and continental usually do better in colder climates. The cloves are larger and easier to peel. A few variety names are ‘Spanish Roja’, ‘German Red’, ‘Carpathian’, and ‘Music’.
Softneck garlic types like silverskin or artichoke are not recommended for northern climates. Numerous strains exist, having been selected over the years by the various companies that produce them for dehydration, or by growers producing them for the fresh market. One reason why industrial farms grow softneck garlic is that the planting process can be mechanized: since they don’t produce a scape, the cloves can be planted upside down. Topsetting garlic cloves must be set upright. Fewer varieties of softneck exist, compared to topsetting. The varieties ‘California Early’ and ‘California Late’ comprise 90% of the softneck types grown.
When to Plant
Vernalization from a period of cold is required in order for the mother bulb to split into cloves. Fall planting is recommended in all parts of the U.S. For spring planting—not
recommended—the bulbs need to be refrigerated at 40°F for 40 days. Fall-planted garlic grows rapidly when the weather warms in spring. Garlic is day-length sensitive and will bulb
in specific areas according to the sun, often near the summer solstice. In the North, plant in October before the ground freezes. This gives the plant time to make good root development but not enough time to make leaf growth. Where winters are milder, garlic can be planted from November through January.
How to Plant
Garlic is propagated vegetatively from the cloves in each bulb. The size of both the clove and the bulb is an important consideration when selecting planting stock. Grade your garlic for
both size and quality. Discard anything that is diseased, small, soft, damaged, or discolored.
This is time-consuming, but important. Crack the bulb into individual cloves. Plant cloves basal plate-side down. Where winters are mild, plant cloves 1 inch deep; where winters are severe, put them 2–4 inches deep.
According to the publication Commercial Storage of Fruits and Vegetables (12), garlic will keep for 6 to 7 months if it is stored at 32° F and at 65 to 70 percent relative humidity. It is important to keep temperature and humidity constant. Any variation in either will initiate sprouting. High humidity will keep the bulbs from dehydrating. A walk-in cooler can make a suitable storage facility. A 25-watt light bulb and a thermostat can be used to provide heat when needed. A fan will keep air circulating.
Stored garlic should be checked monthly. White mold is a postharvest disease that may show up in stored garlic. It is caused by the fungus Penicillium, which will sprorulate and spread.
This how-to video from the nonprofit group KGI (http://KitchenGardeners.org ) walks you through the steps of harvesting, curing and storing garlic.