The principal source was the USA, initially from New York State, later California and Oregon. But hops were imported from every region in the world. Large quantities of European hops were imported, too. Bavarian and Bohemian hops were considered equal to quality UK hops. Lower quality hops from Belgium and France were also used, despite brewers not much caring for them. They did have the big advantage of being cheap.
Despite the UK being one of the world’s biggest producers of hops, it was enough to meet the needs of brewing. The industry was dependent on importing large quantities of hops.
There was an enormous fall in the quantity of hops being imported, down to just a few hundred cwts. In 1918. Oddly, one country from which supplies continued to be imported was Belgium, despite most of the country being occupied by the Germans. The one corner still in Belgian hands just happened to include Poperinge, home to the Belgian hop industry.
You can see from the table below that hop imports came to an almost complete stop in the final two years of the war:
|Hop production and imports (cwt)|
|year||Acreage||UK production||yield per acre||Average price of English hops||net imports of foreign hops||exports of British hops|
|1928 Brewers' Almanack, page 119|
The price of hops also increased dramatically to around three times the pre-war level.
The above is an excerpt from Armistice, my this wonderful book on brewing in WW I.
a Kindle version.