My softneck garlic does this all the time. Mostly blots 1/2 way up the stem before the bulbils explode out! I think it happens because of my colder norther climate. Maybe you had a rough winter?

The purple striped soft neck I plant does this, too. Some years more so than others, but generally about 1/2 the crop will scape. This year far less and we did, in fact, have a warmer than usual winter.

Some softnecks can bolt if stressed, such as very cold weather. Silverskins are normally considered a strain that "infrequently, incompletely, or weakly" bolt, but they are more sensitive than others to climate.

In "The Complete Book of Garlic", the author Ted Jordan Meredith states:

"Creole and Silverskin cultivars are in groups that are at the genetic threshold for bolting, where environmental conditions play a major role in dictating whether bolting will occur",

and

"Under some growing conditions Silverskins almost always bolt, while under other growing conditions they almost never do."

According to this book, some Silverskins may fully bolt in northern climates, especially if they were grown in warmer climates and then planted up north. Since you are in Washington, I suspect this may be the cause.

Other cultivars that may or may not bolt according to environmental conditions include Creoles, Turbans, and Asiatics.

As an organic garlic farmer Travis, I'm sure you have a well worn copy of Ron Engeland's book "Growing Great Garlic", but if you don't yet have Meredith's book I highly recommend it! It is beautifully illustrated and very comprehensive.

TomNJ