Onions are a popular and rewarding vegetable, but successful cultivation depends heavily on planting at the correct time. New Jersey’s climate, with its specific temperature fluctuations and seasonal day length, requires gardeners to follow a precise schedule to ensure proper bulb development. Understanding the difference between onion types and preparing the soil correctly are just as important. Aligning the planting method with regional growing conditions maximizes the yield of large, mature onions.
Selecting the Right Onion Type for New Jersey
The primary factor in choosing an onion variety is its photoperiod, the amount of daylight required to trigger bulb formation. Onions are classified into three groups: short-day, intermediate-day (or day-neutral), and long-day varieties. New Jersey’s latitude requires either long-day or intermediate-day types to produce a large bulb. Long-day onions need approximately 14 to 16 hours of daylight to begin bulbing, typical of the northern United States during summer.
Intermediate-day varieties, requiring 12 to 14 hours of daylight, also perform well in the state, especially in central and southern areas. Planting a short-day variety, which begins bulbing with only 10 to 12 hours of light, will result in a premature, small bulb because the plant will not have enough time to develop sufficient foliage for energy storage. Onions can be purchased as seeds, small dry bulbs called sets, or young plants known as transplants. Transplants offer the highest success rate and are generally preferred for growing large, dry bulbs.
Spring Planting Schedule
The best time to plant onions in New Jersey is in late winter or very early spring, as soon as the soil is workable. Onions are cold-hardy and need a long period of vegetative growth before increasing summer day length triggers bulbing. Planting too late reduces the time for the tops to grow, resulting in smaller bulbs.
Onion sets or transplants should be planted outdoors approximately four to six weeks before the average last expected frost date for your specific area. This typically means planting can begin as early as late February or early March in the milder southern regions, and through March into early April for northern New Jersey. The young plants can tolerate temperatures down to the mid-20s Fahrenheit, making them one of the first crops to go into the garden.
If starting from seeds, the process must begin much earlier indoors to produce transplants of sufficient size. Onion seeds require an extended 10 to 12 weeks of indoor growth before they are ready to be moved outside. This places the indoor starting window in late January or early February to prepare for the March or April outdoor planting date. Direct seeding outdoors is generally less successful for dry bulb production, but if attempted, it should be done as soon as the soil is workable, planting the seeds about a half-inch deep.
Essential Soil Preparation and Location
Onions thrive in full, unobstructed sunlight for at least six hours daily. The energy captured by the leaves directly determines the eventual size of the bulb. Soil structure is equally important for forming well-shaped bulbs.
Onions require loose, well-draining soil, ideally a sandy to silty loam; heavy clay soils impede bulb expansion and drainage. Since they have shallow root systems, excellent drainage is necessary to prevent rot and disease. The ideal soil pH ranges from slightly acidic to neutral, specifically between 6.2 and 6.8.
Amending the planting bed with organic matter, such as compost or well-rotted manure, before planting improves drainage and fertility. Onions are heavy feeders, requiring nitrogen for robust top growth that must be maximized before bulbing begins. Applying a nitrogen-rich fertilizer during the early growth phase, and again a month later, supports the development of large, healthy tops and ultimately large bulbs.
Harvesting and Curing
Onions are typically ready for harvest in mid-to-late summer, signaled by distinct visual cues. The tops of the plants will begin to yellow, weaken, and eventually fall over naturally. Once about half of the tops have flopped, the onions are ready to be lifted from the soil within a week or two.
Stop watering the onions a few days before harvest to help the outer skins dry out. Carefully lift the bulbs using a garden fork to avoid bruising, which can lead to storage rot. After harvesting, the bulbs must undergo curing, a process that dries the neck and outer layers for long-term storage.
Curing involves placing the onions in a warm, dry, and well-ventilated area, such as a garage or shed, out of direct sunlight. Spread them in a single layer for two to three weeks until the neck is completely dry and the outer skin is papery. Once cured, trim the tops to about one inch above the bulb, and store the onions in a cool, dark location between 32 and 40 degrees Fahrenheit.