Gardening Tip of the Week – How to Grow Onions
The Long and Short of Growing Onions
“What a difference a day makes.” That’s especially true when it comes to growing onions, since this versatile vegetable forms bulbs in response to the length of the day. There are three types of onions and each one is better suited for growing in different regions of the country. “Long-day” onion varieties will quit forming tops and begin to form bulbs when the day length reaches 14 to 16 hours. “Short-day” onions will start making bulbs much earlier in the year when there are only 10 to 12 hours of daylight. There also are day-neutral onions and as the name suggests, regardless of the number of daylight hours, you can count on them to form bulbs. Here in North Texas short-day onions work best.
Onions are biennial, which means that it takes two full years to grow an onion from seed to bulb. No wonder most people prefer to start with transplants.
When to Plant
Transplants are available as either small (immature) bulbs — called “buttons” or as “slips.” To produce the largest, best tasting bulbs, you must get those transplants into the ground early. Onions must be properly chilled in the ground. For buttons this means early fall (usually before October 15). Slips must be planted in late December or early January when day length and temperature are just right.
- 1015Y Texas SuperSweet — Large, sweet yellow onion. Matures early. Very disease resistant and keeps better than most other short day onions
- Yellow Granex (Vidalia) — This large, sweet yellow variety is the earliest-maturing variety available. Best eaten raw. Also known as the Maui or Noonday onion.
- White Granex — White Vidalia type sweet onion.
- White Bermuda (Crystal Wax) — Great for bunching or for eating raw. White Bermudas are extremely mild but do not store well.
- Red (Burgundy) Bermuda — Mild and sweet. Great for sandwiches.
Where to Plant
Like most vegetables, onions must be planted in full sun. Full sun is generally considered to be 6 hours or more of direct daylight. Less than that and your bulbs may not form properly in time for harvest.
Prepare Your Beds
Onions need loose, well-drained soil. Raised beds are best. Dense clay soils should be heavily amended with good quality organic compost and lava sand, expanded shale, Texas Greensand or other soil amendments that improve soil porosity and moisture retention.
How to Plant
Onions are slow growers. As mentioned above, planting from seed takes two full years. Green onions can be ready in 20 to 30 days after planting but dry bulb onions can take 100 to 175 days to reach maturity.
Some gardeners like to dig trenches and then just line the plants up in the trench. Other people prefer to make a separate hole for each plant. Either way, include some soft rock phosphate with each plant.
Push each button or slip into the ground about two inches deep. Buttons should be planted with the pointy end up.
Keep rows about 12 inches apart and each transplant about five inches apart. The area around each transplant should be about 6 to 12 inches for the onion bulb to grow. Water regularly and thoroughly. Be careful not to overwater. If the soil remains wet, your plants will rot in the ground.
After planting, top dress with compost and mulch.
Care and Maintenance
Keep in mind that the edible portion of the plant is the bulb. If you’re an onion, proper bulb development is everything.
We’ve already discussed the three most important factors: choosing short day varieties and cold weather planting. The third factor is fertilization.
Onions prefer a high nitrogen fertilizer — nitrogen actually helps lower the pH of your soil, which helps with bulb formation. A couple of good fertilizer choices would cottonseed meal or alfalfa meal. Fertilize every two weeks during the growing season.
Keep beds free of weeds. Mulching will help repress weeds and retain moisture.
Pests and Diseases
The most common problems with onions are blight, purple blotch, and thrips.
Both blight and purple blotch are caused by fungus, and are generally caused by excessive moisture (over watering!) Allow the soil to dry out between waterings. Use your finger to check the soil. Push it down to at least the second knuckle. If the soil is still moist, don’t water.
Onion crops should be rotated every year to prevent the spread of these diseases
Thrips are tiny insects that suck the juices out of the plant. They’re easily controlled with organic insecticidal soap or 70% Neem extract.
Harvesting and storing onions
Stop fertilizing onions when they begin to push the soil away and start the bulbing process. The onion will first form a top and then, depending on the onion variety and length of daylight, start to form the bulb.
The size of the onion bulb is determined by the number and size of the green stocks or tops at the time of bulb maturity. For each leaf there will be a ring of onion — the larger the leaf, the larger the ring will be.
You can harvest them early – in which case you would have green onions or scallions – but you need to eat them right away. They cannot be stored unless they are fully mature at the time of harvest.
When onions are fully mature and have stopped developing, the tops will wither and die. Wait until most of the tops have fallen over. This indicates that the plant is going into dormancy.
At this stage, stop watering and leave the onions in the ground for another 7 to 14 days to allow them to mature fully.
Bulb plants such as onions need to be removed very carefully. Use a gardening fork to gently dig under the plant and lift it to the surface. If you try to pull it out by the top, most likely the top will just break off. You want to avoid damaging it. If you damage the skin you can ruin the plant.
Proper drying of onions is essential – otherwise they will quickly rot. Hang in a cool, dry place for at least 1 week before using them.
Check harvested bulbs for any damage. Soft bulbs indicate internal rot. Throw out any bad ones immediately.
Allow onions to dry for several weeks before you store them. Spread them out on an open screen off the ground to dry. Store at 40 to 50 degrees F in braids or with the stems broken off. Mature, dry-skinned bulbs like it cool and dry.
Visit our Organic Gardening Department for all the supplies you need to grow bigger, better onions. Then let our staff show you how to have a “no tears” growing experience.