Fall-planted onions are a great way to enjoy an earlier and larger bulbed harvest from next year’s garden. In most cases, fall planting is not as successful as spring planting because the bulb needs to store more food reserves over the winter, but it has been observed that by harvesting onions from fall-planted bulbs the onion quality is better than those planted in the spring.
When planting your bulbs in autumn, the soil is warmer, so that they may establish a strong root system before winter sets in allowing for faster growth. As the cold chill of winter arrives, the crop goes dormant. Then, as the temperatures and soil warm again in early spring, the onions come back to life.
Onions can be planted in both the spring and fall seasons, depending on where you live. Generally speaking, plant onion sets outdoors when the weather is cool–not cold. It is better to use bulbs than seeds because they will establish quicker in the soil and grow larger onions.
- A fall-planted crop of onions needs at least 4 to 6 weeks of warm temperatures to become established in the ground. The bulbs sprout and establish in the soil, and when the cold chill of winter arrives, the crop goes dormant. They will remain dormant during the cool season but be all primed and ready to grow when spring arrives. Fall onions often grow much larger and better-tasting than those planted in the spring.
- In regions with a frigid winter, it’s best to plant onion sets in the spring as soon as the ground can be worked—usually in March or April. Ideally, time your planting so that outdoor temperatures no longer dip below 28°F (-2°C) after the onions are in the ground.
When planting onions in the fall, it's important to keep in mind that they are not cold-loving plants, so they need protection from frost. Growing onions in both fall and spring starts with great soil. Find a location that has well-draining soil and is on a slope for good drainage. It is important to keep your onion bed away from low-lying areas that retain water. Prepare your soil by tilling or spading to loosen it and remove any large rocks or debris so they don’t disturb your onion roots as they grow. Organic material such as compost or manure needs to be added to the bottom of the planting hole.
Onions are planted in trenches that are covered with straw, leaves, or sawdust. Dig a trench that is two inches deep and a few inches wide. Set the bulbs in the compost with the pointy end facing up. This will ensure the bulb will sprout quickly through the soil. Space the bulbs 4 to 6 inches apart. The spacing is important because the harvest is larger when planted in the fall. Cover the trench with soil and compost. Top the trench with straw, leaves, or sawdust.
When the growth comes through the surface, cover it with more straw or shredded leaves. This will protect your onions in the winter, keeps away the weeds, and keeps the soil moist. As long as you have rain weekly, your onions will be fine, otherwise, water them as needed. Once winter arrives, the plant goes dormant, and you will not need to water them.
With spring’s arrival, your onions will come back to life. Bulbs planted in the fall are ready in the summer for harvesting.