I wouldn't be quick to use twice the amount with a double row, but I'd be prepared to fertilize more often - if it becomes necessary. What you use, and how much at each time, is your choice.

I use Urea on my onions after the initial feeding and just sprinkle it around prior to a decent (1/4"+) rain. Nitrogen is really all they need after roots are established.

1/2 cup for 20' row is essentially nothing. Rows 8" apart can be treated like individual rows. You just side dress on the outside of each row and not in between the two. OR like rgreen said side dress down the center of the 2 rows and apply more often.

" I threw down"... so are you just tossing it around on the surface? It works much more effectively and much less waste when mixed in with soil around root level.

Dave

I say “threw down” but I did actually incorporate it.

It was Dixondale’s own website that said to do that, Dave! The half cup...

Now that it has actually warmed up enough that they started pushing a little new growth, I feel like the roots have grown enough to focus on the N side of things.

"It was Dixondale’s own website that said to do that, Dave! The half cup..."

That all depends on the fertilizer used. You used 10-10-10 so what do the directions on its bag say?

Note that Dixondale recommends higher dose fertilizers - generally 1.5-2x as strong on N and in some cases 2x more P. They give the example: "the rate of Ammonium Sulfate to apply 20 units per acre is 1 cup per
20'. If using manure, the rate will be 10 cups per 20' in most cases.
Blood meal's formulation is usually 13-0-0, indicating a rate of 1.6
cups per 20' in your garden."

Dave

OK, I have a total of 80 feet of row if you consider that my double rows are each their own row – Two 20’ Do le rows. But how “wide” are they as far as calculating N is concerned? They are still small plants so the root zones probably don’t go that far out yet.

If I assume each “row” is only a foot wide, then I figure I need about 3 pounds of 10-10-10 using their recommendations.

I may go out and grab either some high nitrogen lawn fertilizer or something like blood meal.

Fair points...But now it’s just bugging me that I can’t figure it out.

So I have four rows. How “wide” are the rows? A foot? I can’t imagine the roots have grown any more than 6" away (on both sides) from the plants yet. So 80 X 1’ wide = 80 square feet.

Using the formula in the link - 80 X 0.0037 = 0.296 lb of N for the entire season (this seems really low) - since 160 lbs of N per acre is the seasonal recommendation.

At the bottom of the page, it says to basically apply N at intervals of 20 ‘units’ every two weeks, more or less, for a total of 160 ‘units’ of N. To put it another way, you apply 1/8 of the amount above each time.

So, 1/8 of the amount above is 0.037 lbs of N, or 0.37 lbs of 10-10-10, each time, which again, seems low!

What a convoluted set of instructions. Lol! I think you forgot step 3 in your calculation (need to account for percentage nitrogen) and you're assuming no nitrogen currently in your soil. Is this a new garden?

Most soil tests don’t reveal nitrogen. I’ve added compost, so I’m sure there’s some in there.

Also - last paragraph, I divided by .10 to account for the fertilizer having 10% nitrogen.

Sorry but you are making it far too complex. A "row" has one dimension - length. All the other math is irrelevant.

Instructions that call for x amount per x # feet of row are just that - the length of the row be it corn or onions or lettuce or whatever - regardless of the crop or the width or where the roots may or may not go. Onions are shallow rooted plants with a root ball approx 2" in diameter.

Width of a row makes no difference and as I said above double planted rows are treated like single rows EXCEPT you apply on the outside of each rather than between the 2 rows placed close together.

So if you have 4 20' long rows each row gets however much your fert calls for for 20'. If you had 1 80' row then the row would get 4 doses (80 div 20 = 4) 1 dose every 20 feet. This is assuming it is given in foot row measurements. Many use square feet, some use lbs. per square feet, etc.

The real issue is the fertilizer you choose to use. 10-10-10 is nothing like anything else but 10-10-10. You can't use the numbers Dixon gives for using 21-0-0 or 13-0-0 etc. You have to use the instructions on the particular product you bought. Since 10-10-10 is not a commonly used onion fertilizer as it is relatively low in N for onions and contains high P and K the onions don't need it would be easier to just buy one of the recommended high N onion fertilizers.

Dave

Dixondale’s link specifically said square feet, not row length, that’s why I asked the question.

My Soil tests out fairly low in P comparatively...would using the higher P be worthwhile at least early on?