Onion sets are small, immature bulbs grown the previous year. They are the most reliable option for gardeners aiming to harvest full-sized onions in the spring after an autumn planting. Using these pre-formed bulbs provides a significant head start over seeds and minimizes the risk of crop failure, making them the preferred choice for overwintering. Finding the appropriate sets requires understanding the specific needs of fall planting and the seasonal nature of their availability from local and online sources.
Selecting the Right Onion Sets for Fall Planting
Choosing the correct onion set is based primarily on the photoperiod, which is the number of daylight hours required to trigger bulbing. For fall planting and overwintering, gardeners must select short-day or intermediate-day varieties, typically suited for mild-winter climates. Short-day varieties, suitable for the deep South, begin to form bulbs with 10 to 12 hours of daylight. Intermediate-day varieties are more versatile, requiring 12 to 14 hours of daylight, and perform well across many mid-latitude regions.
Using a long-day variety in a southern or intermediate climate will prevent the plant from forming a proper bulb. Set quality is also important for preventing premature flowering, known as bolting. Sets that are too large, generally exceeding the size of a dime or a marble, are more likely to bolt as the temperature rises in spring. The ideal onion set is small, firm, and shows no signs of sprouting or mold growth, ensuring the plant focuses its energy on root and leaf development over the winter.
Local Retailers and Seasonal Availability
Many gardeners begin their search at physical locations, including local nurseries, independent garden centers, and large home improvement stores. These local sources generally offer a limited selection, often selling generic red, white, or yellow sets without specific varietal names or day-length information. Availability at these retailers is highly seasonal and constrained to a short window, typically starting in late summer and extending into early fall for overwintering crops.
Because the stock is limited and often arrives only once, sets for fall planting can sell out quickly. When purchasing sets in person, inspect the quality carefully. Avoid any sets that feel soft, appear shriveled, or show signs of blue or green mold, as these indicate decay or disease. Reject any sets that have already begun to sprout, as this indicates the bulb has broken dormancy and will put its energy into top growth at the wrong time.
Specialized Online and Mail-Order Catalogs
For gardeners seeking specific day-length varieties or a wider selection of named cultivars, specialized online nurseries and mail-order seed houses are the better option. These vendors, which often include large seed companies and dedicated onion growers, provide access to the specific short-day and intermediate-day types necessary for successful fall planting. The inventory from these specialized sources is generally of higher quality and is certified free from common diseases, such as white rot.
Acquiring sets from these vendors requires planning and pre-ordering, often beginning several months in advance to secure a fall shipping date. Shipping logistics for dormant bulbs are carefully managed to ensure the sets arrive at the appropriate planting time in late summer or early fall. Upon arrival, the sets should be immediately removed from any sealed packaging and inspected for firmness and health, as shipping can occasionally lead to moisture or damage.