Onions are a garden staple, celebrated for their ease of cultivation, minimal space requirements, and impressive storage capabilities that extend throughout winter. Their versatility in the kitchen is unmatched, enhancing everything from savory sauces and vibrant salsas to crisp salads and, for the grilling enthusiast, thick slices caramelized on a burger. As a cool-season root vegetable, onions are among the first crops you can plant each year, offering gardeners an early start to the growing season.
Before diving in, the crucial first step is deciding what type of onion best suits your needs. Yellow onions are a popular choice for their all-around culinary applications, while red onions bring color and zest to summer dishes. Consider the storage life of different varieties; some are best enjoyed fresh within a month, while others can be stored for up to five months, ensuring a supply well into the colder months. Local garden centers are invaluable resources for variety recommendations suited to your specific climate and growing conditions. For a broader overview of onion varieties, resources like Gardener’s Path offer excellent guides.
Key aspects to successful onion cultivation include understanding that they are a cool-weather crop, optimal planting depths and spacing, consistent watering, timely harvesting when tops begin to fall, and proper curing for long-term storage. Additionally, onions are known to deter aphids, making them beneficial companion plants for crops like lettuce.
Understanding Your Onion Options: Seeds, Sets, or Plants?
Beyond variety selection, you have choices in how you start your onion crop: seeds, sets, and plants, each with its own advantages.
Starting from Onion Seeds
Onion seeds are the most economical starting point. Purchasing seeds allows for a wide selection of varieties and is the most budget-friendly method. However, growing from seed requires more effort and time. Seed-started onions need thinning after sprouting to ensure adequate spacing and take longer to mature into full-sized bulbs compared to sets or plants. Seeds are ideal for gardeners wanting to start onions indoors or in a greenhouse, giving them a head start before the outdoor planting season begins.
Using Onion Sets
Onion sets are a popular and convenient option for many gardeners. These are immature onion bulbs grown from seed the previous season and harvested before full maturity. They enter dormancy over winter and are ready to plant the following spring. Onion sets are easy to handle and plant directly into the garden, simplifying spacing and eliminating the need for thinning. Typically sold by weight or in bags, sets offer a middle-ground approach, balancing cost and convenience. For those interested in saving money and ensuring a continuous supply, growing your own onion sets each year is feasible. Harvest to Table offers valuable resources on how to grow your own onion sets.
Opting for Onion Plants
Onion plants, often sold in bunches with vibrant green sprouts, are a preferred method for many, including experienced gardeners. These are young onion plants started earlier in the current season. Similar to sets, onion plants are planted directly into the garden without needing thinning. The primary advantage of onion plants is their higher success rate, particularly for those who have struggled with sets in the past. Plants tend to establish quickly and consistently produce robust, full-sized onions.
Planting Your Onions for a Bountiful Harvest
Growing onions successfully hinges on providing them with the right environment. They thrive in well-drained soil, ample sunlight, and consistent watering. While they aren’t particularly demanding, proper soil preparation is key to a healthy onion crop.
Soil Preparation for Onions
Like most garden vegetables, onions benefit significantly from well-prepared soil. They prefer loose, well-draining soil rich in organic matter and slightly acidic, with an ideal pH between 6.0 and 7.0. Enriching your soil with organic materials like compost or well-rotted manure is highly beneficial. These amendments improve soil structure, drainage, and fertility. Avoid using fresh manure, as it can introduce harmful bacteria and weed seeds.
According to the University of Minnesota Extension, phosphorus and potassium should be applied based on soil test recommendations. Many soils already contain sufficient phosphorus, so using a low- or no-phosphorus fertilizer is advisable unless a soil test indicates otherwise. Nitrogen is crucial for onion growth, but excessive nitrogen can lead to issues like delayed maturity, thick necks, soft bulbs, and poor storage quality. Side-dressing with a nitrogen fertilizer after the root systems are established is recommended, typically once or twice during the growing season. Urea (45-0-0) applied at a rate of 0.25 to 0.5 pounds per 25 feet of row, spread alongside the plants and lightly scratched into the soil, is often effective. It’s crucial to avoid “weed and feed” fertilizers on vegetable gardens as they contain herbicides harmful to vegetable plants.
Planting Seeds, Sets, and Plants
The planting method varies slightly depending on whether you are using seeds, sets, or plants.
Planting Onion Seeds
Seeds can be sown as soon as the soil is workable in early spring.
- Sow seeds in a band about 2 inches wide.
- Plant seeds 1/4 to 1/2 inch deep.
- Space rows 12 to 18 inches apart.
- After germination, thin seedlings to 3 to 4 inches apart to allow for bulb development.
Always refer to seed packet instructions for variety-specific planting recommendations.
Two children transplanting onion seedlings into garden soil.
Planting Onion Sets and Plants
Onion sets and transplants share a similar planting process. They are cold-hardy and can be planted when soil temperatures reach 50 degrees Fahrenheit, typically in April or early May for regions like Minnesota (Zone 4b).
Before planting, trim the roots of onion plants to about 2 inches and the tops to approximately 4 inches. For sets, ensure the pointy tip is facing upwards when planting.
- Create a furrow in the prepared soil.
- Plant sets or plants about 2 inches deep.
- Space them 3 to 4 inches apart.
- Maintain row spacing of 12 to 16 inches.
Caring for Your Growing Onions
Consistent care is vital for healthy onion development. Onions have shallow root systems and require regular watering, especially during bulb formation.
Watering and Weed Control
Onions need about one inch of water per week, either from rainfall or irrigation. Sandy soils may require more frequent watering. Monitor soil moisture and water deeply whenever the top inch of soil feels dry. Weed control is also important, as weeds compete with onions for nutrients, water, and sunlight. Shallow hoeing between rows helps manage weeds, but be careful not to damage the shallow onion roots. Mulching with organic materials like straw or grass clippings (ensure they are weed-free) can suppress weeds, conserve soil moisture, and regulate soil temperature. Pine shavings can also be used as mulch but be mindful of their potential to increase soil acidity.
Harvesting and Storing Onions for Longevity
Knowing when and how to harvest and store onions properly is crucial for enjoying your harvest throughout the year.
Harvesting Onions
Harvest time is indicated when onion tops begin to fall over and turn brown, signaling maturity and the end of bulb growth. This typically occurs in late summer or early fall. While a mass harvest is best when most tops have fallen, you can harvest some onions earlier for fresh use as needed throughout the growing season. Avoid leaving mature onions in wet soil for extended periods after they have stopped growing, as this can lead to rot.
Choose a dry, sunny day for harvesting. Often, gently pulling on the bulb (avoiding the leaves) is sufficient to lift the onion. If the soil is compact, use a garden fork or shovel to loosen the soil around the onion, being careful not to damage the bulb. Leave the tops intact during harvest, as cutting them can create entry points for bacteria during curing.
Curing Onions for Long-Term Storage
Curing is essential for extending the storage life of onions and preventing rot. After harvesting, allow the onions to dry in a sunny spot for a day or two to dry out the roots. Next, move them to a shady, well-ventilated area outdoors, or an indoor space like a garage or basement if rain is expected. Spread the onions out in a single layer to ensure good air circulation and prevent moisture buildup. Proper curing takes about two to three weeks, during which the onions should dry thoroughly.
Once cured, the roots and tops will be brittle and dry, the outer skins papery, and the outer layer will easily flake off. For storage, you can trim the tops and roots and remove the outermost skin layer for a cleaner appearance, or braid the stems together for hanging storage. Braiding promotes airflow and may further extend shelf life. Properly cured onions can last for several months, often into the winter.
Companion Planting with Onions
Onions are excellent companion plants in the garden, primarily due to their pungent odor, which repels various pests. They are particularly beneficial for members of the cabbage family, such as broccoli, kale, kohlrabi, and Brussels sprouts, as they deter cabbage worms. Onions also repel aphids and Japanese beetles, protecting vulnerable plants like lettuce, tomatoes, and strawberries. Other beneficial companion plants for onions include carrots, dill, beets, and peppers.
However, avoid planting onions near peas, beans, and asparagus, as they may negatively affect the flavor of these crops. Also, avoid planting onions with other members of the onion family, such as shallots or leeks, to minimize the risk of spreading onion maggots and other onion-specific pests and diseases.
By following these comprehensive steps, you can successfully grow onions in your garden, ensuring a plentiful supply for your culinary needs throughout the year. Happy gardening!
