Onions make a popular vegetable because they grow easily in virtually any area of the United States. The majority of gardeners use transplants and seedlings to grow onions. According to the University of Minnesota, growers can eat onions at any stage of growth. Onions are actually biennial plants that gardeners grow as annuals because they are easy to grow, provide many uses in the kitchen and store well.
Onions need plenty of room to grow and properly form bulbs. Texas A&M recommends planting onions approximately 1 inch deep. Allow 4 inches between onion plants.
Onions grow better in soil that has a phosphorous band for larger and higher bulb yields. Texas A&M recommends using 10-20-10 fertilizer several inches below the soil depth where the onion transplants are placed. For example, if you plant onions 1 inch deep, there should be 2 inches of soil on top of the phosphorous band.
Onions require a great deal of water to grow, particularly near harvest time. Keep the soil moist but not compacted and soggy. Texas A&M suggests watering onions after each application of fertilizing. Water transplants immediately after planting, to encourage the onion seedlings to continue growth.
It is important to plant onions that are the appropriate day length for your growing region. According to the University of Minnesota, onions that receive more than 12 hours of daylight are long day onions. Onions that receive less than 12 hours of daylight are short day onions. Most southern regions require short day onion varieties and northern regions require long day varieties. Selecting the right type of plant based on day length is important prior to planting onions.
Onion transplants and seedlings do not do well if they are transferred from indoor conditions to outdoor conditions without hardening. According to the University of Minnesota, hardening requires setting the plants outdoor for an initial short period of time and extending the length daily over a two-week period. This gets the onions acclimated and ready to move permanently to a raised bed outdoors.