Onion sets offer home gardeners a reliable path to harvest compared to starting from seed. These are small, immature onion bulbs grown from seed the previous year and harvested while dormant. Sets are prized for their convenience and hardiness, ensuring a quick start to the season. Planting sets boasts a much higher success rate than direct sowing seeds, which often have slow and patchy germination. This method allows the gardener to harvest full-sized bulbs up to two months sooner.
Local and Retail Sources for Immediate Purchase
Gardeners seeking immediate availability often turn to local garden centers and nurseries. These establishments usually stock varieties that are well-suited for the regional climate, and staff can provide specific advice regarding planting times and local soil amendments. While the selection may be limited to common yellow, white, and red varieties, the quality is often superior, though the cost per set may be slightly higher.
Big box stores and large home improvement centers also offer onion sets, focusing on broad availability and competitive pricing during the peak spring planting window. These retailers ensure accessibility for a wide range of customers but tend to carry generic types, often labeled only by color rather than named varietals. A potential drawback of buying from these high-volume sources is that the sets may have been improperly stored, potentially leading to lower quality or greater risk of rot.
Farmer’s markets and agricultural co-ops are excellent resources for finding unique regional selections. These local outlets often source sets directly from smaller growers, providing varieties adapted to the immediate microclimate. However, relying solely on local retail sources means accepting a limited range of specific cultivars available on-site. Those looking for specialized or bulk quantities often need to look beyond the immediate local market.
Online Specialists and Direct Suppliers
Specialized online seed and bulb companies provide a vast inventory that far exceeds the selections available at most physical retail locations. These suppliers are the primary source for gardeners seeking unique, heritage, or specialty onion varieties. Buying online is also the most practical way to purchase onion sets in large, cost-effective bulk quantities for extensive garden operations.
The most significant benefit of purchasing from an online specialist is access to sets optimized for specific photoperiods, which is crucial for successful bulb formation. Onions are categorized as long-day, short-day, or intermediate-day, based on the number of daylight hours required to trigger bulbing. Long-day sets, needing 14 to 16 hours of light, are suited for northern latitudes, while short-day sets, needing only 10 to 12 hours, are best for southern regions. Planting the wrong type for a region will result in small bulbs or only green tops, making the correct photoperiod selection essential.
Purchasing online requires careful logistical planning, as sets must be ordered well in advance of the desired planting date. Most reputable suppliers offer a shipping calendar, often shipping sets weekly from mid-January through April to align with the appropriate planting windows across different regions. Gardeners must confirm their local planting timeline and choose a shipping date that allows for immediate planting upon arrival. Although they arrive dormant and dry, the sets should be planted quickly, as holding them for too long increases the risk of premature sprouting or drying out.
Essential Timing and Quality Checks Before Buying
The timing of the purchase is critical, as quality and availability are highest immediately upon arrival at retailers in late winter or early spring. Gardeners are advised to buy their sets as soon as they become available locally to secure the best stock before it is picked over or improperly stored. For most temperate regions, the ideal purchase period is from late February through early April, allowing the sets to be planted four to six weeks before the last expected spring frost.
A careful quality check is necessary regardless of whether the sets are bought online or locally to ensure a healthy harvest. Healthy sets should feel rock-hard when gently squeezed and have a dry, papery outer skin. Any sign of mushiness, soft spots, a musty odor, or visible mold indicates that the set is already deteriorating and should be avoided. While a tiny green tip is acceptable, sets with long, two-inch sprouts are stressed and will likely not perform well.
The physical size of the set is a highly specific factor that determines its ultimate success; ideally, sets should measure between one-half and three-quarters of an inch in diameter. Sets that are too small often produce diminutive bulbs. Those larger than one inch are significantly more likely to bolt, or prematurely flower. Bolting causes the plant to divert energy into seed production rather than bulb growth, resulting in a small, woody onion with poor storage potential. If sets are purchased before the planting date, they should be stored in a cool, dry area, ideally between 40 and 50°F. Storing them in a mesh bag or a ventilated container prevents moisture buildup, and refrigeration must be avoided as the cold temperatures can prematurely trigger the bolting process.