Tirpitz claimed in his memoirs Germany should have crash imported strategic materials like fertilizers and copper before the war started (for copper sulfate used as a fungicide to spray on potatoes). By early July a fight was going to be likely to happen and the Germans wasted a good solid 3 weeks they could have imported stuff, brought home merchants, sent stuff to colonies etc.
Using their 1870 experience the French had been beat quickly but the war continued for some time after, so even if a German victory takes Paris, blockade conditions might last for some time so preparation would be reasonable even if a quick victory was thought to happen.
Certainly strategic metals and rubber could have been stored for years as a strategic reserve for an eventual war (unsure how long you could store nitrates). The seven years war being so much a part of Prussian military lore that it would seem negligent for a country who had been through that not to store up for a similar such war.
But failing that, I agree with Wilking's comment above, that the Germans made things worse by their own economy screw ups and USW closed any remaining blockade loopholes. Those things were easily avoidable.