My onion plant order is placed! The only allium I will have to start from seed this year will be the Saffron shallots. I took other bloggers’ advice and ordered my plants directly from Dixondale Farms. Not only is the price cheaper for the two bundles I was planning to order, but it gets cheaper by the bundle, so it’s hard to resist. In addition to Copra and Red Zeppelin, I wound up ordering the Tropea onions I usually grow as well as a mixed bundle of intermediate day onions (Candy, Red Candy, and Super Star). So I will have 200-280 plants showing up mid-April and just have to figure where I will put them.
Dixondale has a lot of growing information and I learned a lot just by watching a couple of their videos. I already knew that up North here I plant long-day onions so that after the solstice when days grow shorter, the onions are triggered to start forming bulbs. But there are some tricks to getting the largest bulbs that’s probably obvious to everyone else, but wasn’t to me.
Supposedly an ideal onion will have about 13 layers or rings (ideal meaning that’s about as much as you can expect to get in a growing season). Each ring in the bulb corresponds to one leaf of the foliage. When daylight triggers bulb formation, the layers start expanding, so the more layers (i.e., the more leaves), the bigger the onion bulb will be. A healthy, rapidly growing onion can grow a new leaf about every two weeks. The plants from Dixondale will have 4-5 leaves and a healthy root structure (versus the 2 leaves that my own transplants have). To get to 13 leaves, it will take another 16-18 weeks after transplant, given ideal conditions. Onions are heavy feeders and require a lot of nitrogen to encourage foliage growth.
So the formula for big onions is:
- Plant as early as you safely can. The clock is ticking and you want as much foliage as you can grow before bulb formation commences. Once the bulb starts forming there will be no more foliage growth.
- Buy plants. Ignore the cost, the extra 2-3 leaves they have over homegrown transplants is worth 4-6 weeks of time in your garden.
- Space onions 4 inches apart in the row, with rows 16 inches apart. Plant onion plants no more than 1 inch deep. The reason for the row spacing is that while onions are shallow rooted, they do develop extensive side roots. In raised beds, they recommend a minimum 4” x 8” spacing. I am going to have to play with the geometry of this for my raised beds. And there is the question of, would I like to have more, smaller onions or fewer but larger?
- Use a general purpose fertilizer with lots of phosphorus (something like 10-20-10) for good root development when planting. Maybe add bone meal to get the extra P. If you are pushing the limit and planting very early, Dixondale has found that high potassium levels in the soil help protect against freeze damage. In addition to NPK, onions require a lot of micro-nutrients for healthy growth, including magnesium, zinc, boron, copper, iron, manganese and molybdenum, so make sure they are in your fertilizer (or throw in a handful of rock dust).
- Then starting at two weeks after planting once roots have established, use a nitrogen fertilizer every two weeks. Stop fertilizing when bulb formation starts.
- When bulb formation starts, make sure the onions have plenty of water. Stop watering when foliage falls over and let the soil dry out before harvesting.
- Watch for onion pests like thrips and spray if needed.
- Use a preventative organic fungicide regularly. Even if fungus disease is not visible, any spores present may increase spoilage and reduce storage time.
The nitrogen fertilizer they recommend is ammonium sulfate, which is a chemical fertilizer and not suited for organic gardens. I will most likely use blood meal. If you have a blood meal rated 13-0-0, you apply a cup per 20 foot of row. I will also be amending the beds with the onions with rock dust and kelp meal to get the micronutrients into the soil.