yeah it is washable but honeslty i wouldnt want to risk it.u can get pockets of old nutes and saltes if u dont get it completly flushed. if money is an issue u can go to home depot.they selll the biggest fucking bags of per/verm i have ever seen.there about 10 dollers a piece and its enough to do a 50/50 mix for several hundred plants.i shit u not"these bags are huuuugeee.there on the verry top shelf.i would pick up one of each and toss the old stuff,but thats just me