I have no idea. Have not seen anything like it. Never grew Sterling, but it is reported as growing a uniform globe shaped bulb.

Maybe Dixondale would know.

They look like cabbages split from too much water - but you say it's been dry.

Now that's strange. I assume the seedlings looked normal when you transplanted them. The tops look normal above ground? For some reason those plants generated two basal plates for the roots to grow out of, but I suppose the question is was the cause physical, chemical, or genetic? I suppose you should probably forward the question to Dixondale.

I just sent an email to Dixondale. The seedlings looked normal when I planted them in late March. I would say that about 1/4th of the Sterlings are in this shape and were sent to the compost pile. The tops were slightly stunted. I try to grow organic, so there were no chemicals added. I have raised beds and rotate crops so there have not been onions in this bed for at least 3 years. This may be or not a clue...they were grown in the same bed next to garlic. I had a nice garlic crop this year, but a few heads that were near these Sterlings were mush. I don't think that overwatering is the case because the beds drain well and we are in a relative drought.

This is the reply from Dixondale Farms

DOUBLE OR SPLIT ONIONS

Double or split onion bulbs are undesirable and are discounted in the
market. The ratio of double or split bulbs is influenced by variety and
environment. Some red varieties will produce a higher percentage of splits
or doubles, if grown at wider spacing's or in thin stands. Also, when plants
are grown in uniform stands, fertilizing at a rate which produces large
yields will result in more doubles than a lower rate.
Onions are prone to physiological disorders that growers should try to
minimize. One such disorder is splits or doubles. This condition is caused
by cultural and environmental factors as well as being influenced by
genetics. Over-fertilization, uneven watering, and temperature fluctuations
(particularly below 20 degrees F) are all believed to influence double
formation. Some red varieties are more prone to production of doubles than
others. Varieties prone to doubling should be seeded a week or so later on
the plant beds as well as transplanted a bit later to minimize this
disorder.

The Did not accurately pinpoint the cause and covered all the bases.

But to me "DOUBLING" is different from splitting. Those Onions have double roots , as if they had been grafted. This is more like a genetic in the seed like identical twins in humans.

Yeah, pretty weaselly language. Is Sterling "a variety prone to doubling?" If so, should they not have mentioned this in their catalog?

Last year all my Sterlings from Dixondale bolted and none of the other three varieties did. I contacted them after that and they gave me a new bunch for this year free. They have been very nice about it, but I now suspect (with no empirical evidence) that there might be a problem with this variety on their end.

This year I grew over-wintered onions from seed (Keepsake from Territorial) with great success and I think that next year I will grow summer onions from seed also. Skip the middle man and save $$$. If I have problems I can buy seedlings from Down to Earth (locally)

In the bottom picture - is that a growth that exits and then returns into the onion? Very strange.

It could be nematode damage - below is a nice page from UC Davis.

Too bad about their reply.

I hope this helps!

Here is a link that might be useful: http://www.ipm.ucdavis.edu/PMG/r584200111.html

Did you send a picture to Dixondale? Because what I am seeing is different than I understand "doubling" to be. I always thought it meant when you have an onion with a single set of roots and two tops/bulbs form off of them. I think you got sent the form letter, and may need to convince someone that your question doesn't fit their form reply. That is if you really want to know :)

I DID send a photo to Dixondale and got another email back from their President which I include below. (to me this is still a mystery)

Uneven irrigation of onion fields increases the incidence of this disorder.

Fields that are over-irrigated, allowed to dry completely and then over-irrigated

again often have many split bulbs. This condition is more prevalent in areas

of the field were stands are thin or uneven. These openings can provide an

entrance for secondary microorganisms, which cause bulb decay.

The Sterling variety is not particularly prone to this splitting of bulbs but the

other varieties may have been more evenly irrigated. We have had no other complaints.

Is there anything different about the soil or drainage in the area you planted the Sterling?

Bruce L Frasier

President

Dixondale Farms, Inc

Well, it seems they are doing their best to help you understand. They have a good reputation, so probably the problem does lie somewhere in your planting area if not in the cultivar. Or maybe a better way to say it is if all other things are equal, maybe that cultivar isn't suited to your conditions. I understand the explanation just fine, it's the same thing that causes splitting in fruits like tomatoes and melons, splits in carrot roots, etc. Were these in a low spot in your garden maybe? You thought you were keeping them evenly watered but weren't? I still haven't seen an onion split from the roots before, but I'm willing to concede that my experience is limited to quite a few less onions than the folks at Dixondale. :)