An onion plant will grow just about anywhere since you can take an onion plant and throw it on bare dirt and it will eventually take root and start to grow.
The first important key is time of planting. Onions have kind of two growing stages. There is the vegetative stage and then the bulbing stage. In the vegetative phase, you need to make sure that you get as much leaf growth on the onion as you can. Each one of the leaves on the onion plant is going to represent a ring on that onion bulb so the more leaves you get the bigger the bulb. Planting early is important to maximize the vegetative stage and get as many leaves as you can.
Planting and irrigation
A drip tape can be laid on a 2 foot row spacing for irrigation of onions. Maximizing on the vegetative stage can be done by giving the onion plenty of water through the drip irrigation system as well as fertilizer injection through the drip.
After having the drip tape laid, onions are planted in double rows. This helps because you can get two rows of onions per one row of drip tape hence maximizing space.
Feeding regime
The second key for growing big onions is feeding. Onions like plenty of water and fertilizer. The first way of feeding onions is through injecting fertilizer in the drip irrigation system. In the early stages, inject 20-20-20 through the drip.
Young onions need phosphorous and potassium to encourage root development. As they grow older they just need nitrogen.
Fertilizer application
As onions grow, you switch to a fertilizer that is just primary nitrogen like chilean nitrate. For side dressing, you can sprinkle the chilean nitrate alongside the onion row.
When it comes to bulbing stage, it is symbolized by plenty of rings on the onion and plenty of water is needed to make the onion big and juicy.
