Onions


Lilly family: Allium

Place of Origin: Southern Russia and Iran

Scientific Name:  Allium cepa L.

Optimal Temperatures for Germination: 60-68℉ (15-20℃)

Optimal Temperatures for Growing: 60-68℉(15-20℃)

Characteristics

Onion varieties range from extremely early-maturing to extremely late maturing. Early-maturing varieties grow quickly, but their storage behavior is not remarkable. Middle and late-maturing varieties grow slowly but have remarkable storage capabilities.  Therefore, if the onions are going to be stored for a long time, choose the middle or late-maturing varieties. (Usually early-maturing varieties taste less bitter while late-maturing varieties taste more so, and it could be that the taste has an effect on how long the onion can be stored.)

Growing onions takes a long time, compared to other crops. When seeding in autumn, the necessary growing period is between 50-60 days before transplanting. Harvesting takes seven months after the seedlings are planted. In northern climes after seedlings are transplanted the growing period is five months until the onions are reading for harvest. 

The optimal temperature for plant growth is around 60℉ (15℃). With very early-maturing varieties, the temperature needed for the bulbs to enlarge is 50℉ (10℃); with early-maturing varieties, the temperature needed for the bulbs to enlarge is 60°F (15℃); and with middle and late-maturing varieties, the temperature needed for the bulbs to enlarge is 68℉ (20℃). Onions are vulnerable to heat and don’t grow well when the temperature becomes more than 77℉ (25℃). When seeding in spring, onions should be transplanted to a cool place in the summer.

When onions are sown early, bolting can easily occur; however, when onions are sown late, the seedlings don’t grow large.  Therefore, it is important to sow seeds at the right time. The time to sow can be determined by the amount of daylight, since the amount of sunlight effects how large the bulbs will grow.  So, chose the variety that will thrive in both the temperature and the length of sunlight for the zone or area where the crop will be grown. Below is a reference for the amount of daylight needed for the different varieties. 

Very early-maturing varieties: Less than 12 hours of daylight

Early-maturing varieties: Around 12.5 hours of daylight

Middle varieties: Around 13 hours of daylight

Late-maturing varieties: Around 13.5 hours of daylight

Very late-maturing varieties: Around 14.5 hours of daylight

Seeding

Choose a nursery bed to grown the seedlings that is both well drained and yet can retain water.  Line sowing results in good seedlings of the same size and shape, as compared to just scattering the seeds or spot sowing. Make the ridges 40-45” (100-120 centimeters) wide and 4-6” (10-15 centimeters) high to grow the seedlings, and level the surface of the soil by using a board or a similar item.

Make shallow ditches with 4” (10 centimeters) between rows. After seeding, slightly cover the seeds with the soil so that seeds can’t be seen, (shallow soil cover leads to simultaneous germination), and water the soil over the seeds. A cheesecloth or matting can be used to cover the seedlings to prevent them from drying out. After the seeds germinate (5 or 6 days), remove the covering immediately in the evening so that young leaves are not burnt from sun exposure. Also, placing compost between the rows can prevent the seedlings from drying out. However, don’t put compost on the lines where seeds are sown because the compost will interrupt germination.

Photograph Caption:  Keep the seedling watered before and after germination.

Growing Seedlings

It is said that how well onion seedlings are growing determines the yield. Therefore, care is needed when growing the seedlings. 

After the seeds germinate, water everyday. For up to a month after seeding, make sure that the soil does not dry out. Thin once or twice. Transplant seedlings after about 55 days have passed after seeding. Before planting of seedlings in their permanent location, gather or add soil around them so that the seedlings grow with good root system. The goal is for the seedlings to be about the same size as a pencil and more than 25 centimeters long.

※ Placing soil around seedlings is not always necessary as it depends on the conditions. When the cover soil is thin after seeding, soil will need to be added.

The seedlings do not need to be protected against insects after they have started to grow.  However, as onions grow slowly, steady weeding will be necessary. 

Until becoming familiar with growing onions, grow a lot of seedlings. Select good seedlings when it comes to planting them in their final location, as this will make it easier to get a good harvest.

Planting in the Permanent Location

In southern locations, plant the seedlings of early-maturing varieties in their intended location around the end of October, and plant the seedlings of middle and late-maturing varieties from the beginning and until the end of November. In general, plant seedlings in two lines on a ridge that is 35” (90 centimeters) wide, and plant seedlings in four lines on the ridge that is 45” (120 centimeters )wide. The planting time changes based on location.  With large seedlings, bolting can easily occur, and with aged seedlings, the bulbs enlarge differently. It is important to plant young seedlings at the correct time based upon their zone. With seedlings that grow for 50-55 days after seeding, the regrowth of roots is remarkable and rooting occurs early. A good seedling is about 10-12” (25-30 centimeters) high, the bulb is near the surface soil and is around a ¼” (6-7 millimeters) in diameter. The day before transplanting, water the soil well so that seedbed soil becomes soft. Plant seedlings quickly before their roots dry. After pushing the bulbs lightly into the soil, water the seedlings. This is crucial for the plants to be able to root.  When planting in their permanent location, do not plant the seedlings deeply in the soil. Green leaves should not be buried. (It is good idea to bury the seedlings at the same depth they were growing at before transplanting.)

In conventional farming, a space of 4” (10 centimeters) between seedlings is common; whereas, in Shumei Natural Agriculture, a space of 6” (15 centimeters) between seedlings is considered good. When you want to harvest large onion bulbs or you want to harvest the onions early, it is also good to transplant the onions with wide spaces between them.

Care for Seedlings after Transplanting

 

Watering

After planting onions in their final location, watering is essential. Especially just after transplanting, as roots have been cut and the amount of water that can be taken in decreases, so plants can’t maintain aerial parts. In many cases, the tips the of plants begin to wither. Some withering cannot be prevented because it is a natural process, but water the plants so that they don’t wither due to a lack of water.

Also, if the soil dries out after transplanting, the plants can’t root well and even good

seedlings will not grow any more. Care is needed since onion plants are planted shallowly, they dry out easily.

Covering the Soil with Grass and Compost

The soil can be covered with grass or compost to prevent it from drying out after the seedlings have been transplanted. Generously covering the soil with grass or compost helps prevent weeds to some extent, and those that do grow are easier to weed out. 

Sometimes seedlings slowly shrink when compared to their size before they were transplanted. This is due to a lack of water, which means that they need to be watered more frequently.

 

If bolting Occurs, Pinch out the Top of Seedlings

With large seedlings are transplanted or when seedlings grow too large before the end of the growing season, bolting can occur. (It is believed that flower bud differentiation occurs when the seedlings have grown to certain extent are exposed to a specific low temperature.)

The stem with a bud grows from the center where the leaves extend from.  upon finding the bud, pinch it out. If a bud is pinched out quickly, the bud can still be harvested and eaten, as the plant’s nutrients are not sent to the stem.  However, the bulb cannot be stored and will need to be eaten soon after it is harvested.

Photograph Caption 2: A stem at the early stages of bolting

Weeding

Even after growing healthy seedlings and even after transplanting, onions grow slowly until it becomes warm, so weeding is indispensable. If the field isn’t weeded, the seedlings are soon covered with weeds after a rain.  Because the roots are still weak after transplanting, try to get rid of weeds when they are young. 

Care for Large Seedlings

As spring approaches in moderate climbs, the seedlings grow quickly. Now, depending on the amount of weeds, seedlings can grow well without weeding. Even so, get rid of the weeds around the base of the plants or the weeds that grow over the plants. When the bulb are enlarging or are being harvested, weeds do not affect the growth of the plants any more. At this time, it is more effective to cut weeds after harvesting rather than consuming a lot of time by weeding frequently.

Photograph Caption #3:  Onions during the later stages of their growth need less care. 

Harvesting

There are various ways of harvesting onions depending on their variety. So, harvest onions in a way that suits the variety. By doing so, bolting can be reduced and onions can be harvested effectively.

Harvesting Spring Onions

Spring onions are mostly early-maturing varieties. Harvest the plants that are still forming bulbs and without cutting their leaves. Usually, the selection of mother bulbs for early-maturing varieties is not done in the early stages of growth to prevent bolting. So, harvesting the plants before the bulbs grow large is effective because bolting can easily occur. Also spring onions do not store well and need to be eaten quickly.

Harvesting Spring Onions after Dormancy

Basically, when temperatures exceed 77°F (25 ℃), the stems and leaves wither and the plants go dormant. Stems fall by themselves and can be easily broken with a slight touch. So, all plants can be felled when some plants fall by themselves. The bulb separated from the stem after the stem withers completely lasts the longest. Even  if harvested early, don’t cut stems quickly, but wait until the onions are ripe and then cut stems. Cut them about 2 centimeters above the top of a bulb.

※A “stem” is the part between a bulb and extending leaves.

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