Initial Instructions
The onion transplants you received from the Onion Shed are alive and ready to go in the ground. The onion plants may appear dry from shipping, but don’t worry, they are dormant and will green up again upon planting. It is best to plant the onions as soon as possible. If you cannot plant them right away, they will still grow even if you wait a couple of weeks. The first thing onion transplants do when planted is establish new roots.
Preparation Before Planting
The best place to plant your onions is in fertile soil in full sun. Raised bed at least 4” high and 20’ wide are a good idea. Rows should be spaced 36” apart. Onion yield and growth can be increased by using phosphorous rich fertilizer, such as 10-20-10. The fertilizer is best placed below the onion plants prior to planting. To fertilize onion plants, dig a trench 4” deep in the bed where you are planting, and place ½ cup of fertilizer every 10 feet in the trench. Cover the trench with 2” of soil, and make sure the transplants are planted about 6” from each side of the trench. Make sure you do not plant directly on the trench!
Planting
Set your onion plants 1” deep every 4” to grow large onions, or set the plants 2” apart for green onions. If you want to grow both types, set the plants every 2” and harvest ever other onion once they are green, allowing the remaining onions to fully mature.
Fertilization
A few weeks after the onions have been planted, they will need an additional dose of nitrogen fertilizer. If soil is acidic (below 6.5 pH), use a fertilizer with a calcium base, such as calcium nitrate. The calcium helps raise soil pH. If soil is alkaline, we recommend using ammonium sulfate, which lowers soil pH. For maximum growth, fertilize your onions every three weeks. For best results, obtaining a soil test and applying fertilizer based on the results. Contact your local extension agent for information obtaining a soil test. Stop fertilizing 3 weeks before you harvest your onions.
For gardeners interested in growing onions organically, Omega Grow for vegetables (http://www.omegagrow.com) is a good product, giving onions the nitrogen that they need.
Watering
You should water your onion transplants immediately after planting. Onions require frequent watering because of their shallow root system. If possible, it is best to water using a soaker hose or some form of drip irrigation. Onions are susceptible to foliage diseases, and it is best to avoid overhead watering. In a typica growing season, onions require about 30” of water. As you approach harvest, the onions will need more water than before. If inadequate water is available, the onion bulbs will not grow as big. As soon as the onion tops dry and fall over, watering should be stopped and the soil should be allowed to dry.
Weed Control
Perhaps the most important aspect of growing onions is weed control. To maximize growth and bulbing, weeds in the onion bed should be strictly controlled. A light mulch of organic matter around the onions will help prevent some weed growth. Make sure to move the mulch as the onions get bigger and start to bulb, to ensure that the onions reach their maximum size. Light cultivation around the onions is necessary throughout the growing season to remove weeds that grow around the plants. Make sure the onions are not disturbed in the process.
It is helpful to use a preemergent herbicide prior to planting your transplants. Two herbicides that work well are Corn Gluten and Treflan. If applied prior to planting, both of these prevent weed growth for up to 6 weeks. Incorporate the herbicide into the top 1” of soil, and the weeds will die as they sprout. There are addiontal preemergent herbicides that can be used, but a license is require use them.
Insects
Like all garden plants, onions are affected by various insects and diseases. Onion thrips are sometimes a problem. Symptoms of onion thrips include gray flecks and black dots on the above ground portion of the growing onion plant. Thrips puncture the surface of the leaves to obtain the juices the plant, causing deformed plants and silvery blotches. Thrips live in weeds over the winter, so the best way to prevent a problem is to keep the garden weed-free, especially over the winter. Pesticides that are effective on thrips include Malathion and Neem Oil.
Onion maggots are the larvae of the onion fly. They feed on the onion bulb below ground. They tunnel through the bulb, and have 3 generations per year! The best way to prevent an infestation of onion maggots is to rotate where you grow onions each year, and to remove onion plant remnants after the growing season. If you have a severe infestation, soil insecticides are effective.
Diseases
Two major diseases are commonly encountered when growing onions: blight and purple blotch. Both of these diseases begin as white spots on the onion leaves, surrounded by green circles. The eventual result of these diseases is leaf death, which causes low yield. To help prevent these diseases, it is essential that onion plants and rows be wide enough apart to allow for air circulation. Additionally, preventative fungicide applications will help keep these diseases from establishing themselves on your plants. There is the potential for these foliar diseases to be transferred to the onion bulb later in the season, causing problems with the bulbs. The only way to prevent this is applying fungicide starting 3 weeks after planting, and repeating the application every 7-14 days throughout the season, until the onion tops fall over. Recommended herbicides include Neem oil, .Maneb, and Seacide.
Harvesting and Storage
Onion plant tops will naturally fall over when the bulbing process is complete. We do not recommend that you bend the tops over, as this will cause decreased bulb size. After the tops have dried and fallen over, pull up the onions and allow them to dry in garden for a few days. You can lean then tops of other onions over the bulbs to prevent the sun from scalding the bulbs. After a few days, they are ready for storage!
Onions last longest in a dry, airy place with adequate ventilation. Place onions in a nylon or mesh sack, braiding the tops together so that the onions don’t touch. An alternative method is to tie the tops together with a plastic tie, making sure the bulbs don’t touch each other. Don’t remove the tops or the roots of the onions until you are ready to use them! Hang the onions over a rafter or on a nail in a cool, dry place, and clip onions off as you use them. Sweet onions tend to have a shorter shelf life then more pungent onions, so we recommend you eat the sweetest varieties first. You should sort your onions every few weeks, to and dispose of the bad onions. This helps the good ones last longer.
