Major nutrient removal figures show that nitrogen and potassium are the nutrients needed in relative greatest quantities in onion and garlic crops. They are fundamental for achieving high marketable yields. High rates of nitrogen are needed to satisfy crop demand.
Onions require a high source of nitrogen. A nitrogen-based fertilizer (ammonium sulfate or ammonium nitrate) should be applied at the rate of one cup per twenty feet of row.
Onions grow best in well-drained soil with pH between 6.0 and 7.0, and high organic matter. Apply phosphorus (P) and potassium (K) according to soil test recommendations.
If the crop growth is poor, foliar application of water soluble NPK fertilizers (20:20:20 or 19:19:19) in onion @ 5g/liter at 30, 45 and 60 days after transplanting is recommended for improved yield.
Feed your onions lots of nitrogen to increase bulb size. Because they are a root vegetable, many people believe that onions require lots of phosphorus, however, for increased onion size, nitrogen is your key nutrient. Each leaf that an onion plant produces means an additional ring on the onion.
If onions are planted too close to one another they will compete with one another, resulting in smaller bulbs. Whether direct seeding, transplanting seedlings or planting onion sets, onions should be spaced 3-4 inches apart to maximize growth.
Osmocote Plus is another fertilizer with a great NPK ratio for onions. This formula uses a ratio of 15-9-12, which leaves your plants with an abundant source of nitrogen.
Like all plants, onions need potash; the more potash they have available the less sulphur they absorb. Using low potash fertilisers will result in smaller, but stronger tasting onions.
If you're short of nitrogen, add compost, aged manure, feather-meal, fish-meal or other high-nitrogen amendments. Incorporate them well before you plant, if possible. You can also add nitrogen later in the fall when the garlic or onion leaves are 4–6 in. high.
Nitrogen is one of the most important nutrients for onion plant growth and development. A typical onion crop will use about 150-200 pounds of actual nitrogen per acre during the growing season, with a majority of the nitrogen taken up after the plant has started to bulb.
Magnesium (Mg) levels in the soil must be adequate for good onion growth.
Onions are heavy feeders. Blood, fish and bone or onion fertiliser is recommended prior to planting and during the growing season.
Onions are heavy feeders, so make sure to provide plant food with plenty of nitrogen, phosphorus and ammonium sulfate. A good rule of thumb is to add one cup of equal parts blood meal and bone meal granule fertilizer every 10 feet of row.
Calcium Deficiency Calcium is a very important nutrient for growth and storage quality of onions.
Just prior to planting, apply a balanced fertilizer, such as 10–20–10, close to where the onions will be planted. Three weeks after planting, the root system will be established, and a biweekly feeding of a nitrogen-heavy fertilizer, like 21–0–0, will keep the foliage growing and a deep green color.
The key ingredient is the Nitrogen, since both Phosphorous and Potassium tend to have high levels in soil testing but are not in a form that is readily available to the plant. Adding additional Phosphorous or Potassium beyond the desired amount will rarely harm the onions.
The main crop that needs attention during August are the onions. Don't feed them anymore nitrogen because this will only develop soft tissue that will produce tender growth that will be prone to disease and also reduces the keeping qualities of onions.
Be careful not to damage onion plants. Apply Seasol (30mL of concentrate per 9 litres of water- standard watering can) weekly to promote strong root/bulb development.
Mulch your onions with hay to keep down the weeds and trap in moisture. In late June to early July you'll start to notice your onion tops falling over. Don't be alarmed! This is part of their natural process and an indication that the bulbs have stopped growing and are ready for fresh eating or curing.
We concluded that chicken manure could be exploited in growing onions with health-promoting properties.
"Sulfur is what builds up in the layers of the onion. When you have a large onion, it's going to be stronger because it's spent more time beneath the ground. The longer an onion sits in the soil, the stronger the sulfur will be," explains Palak Patel, a chef and educator at the Institute of Culinary Education.
Most onions require about 30 inches of water per season to grow a good crop with drip irrigation. The key is to provide about 0.3 – 0.4 inches/day – drip irrigation is the best way to apply small amounts of water frequently.
Onions should be planted so that the bulb is barely covered by the soil. If they are planted any deeper, they will grow shoots but are not likely to make bulbs.