Question
I have had moderate success with Spanish & Red onions,using 20-20-20 granular, should I be using a different type like 5-15-5?  What would you recommend to get those large bulbs? You have given me advice before Ken and again I thank you in advance.  oh yes I live in Trenton Ont. Canada zone 5.

Answer
20-20-20 is not bad, but for oninons I would actually recommend 5-10-10, or 10-20-20 if you can find them. You can also switch to 5-15-5, but then add some extra potassium (0-0-50).. just a sprinkle..

I find 10-20-20 in lawn sections of the garden center. In spring and fall, some brands have these ratios. Normally lawn fertilizer has higher first numbers, such as 29-3-4, 20-10-10 etc (and they should not be used on onions). But try to look for a 10-20-20 formular. I buy 40 lbs for $18 USD which is cheaper than buying 5 lbs bags of 5-10-10.

You generally want the phosphorous and potassium (2nd and 3rd numbers on the bags) to be twice as high as the first number when using on bulbs.

E.g. 10-20-20, 5-10-10, etc. The latter is often sold as "tomato" fertilizers.