I have loads of containers which I use to grow annuals. The first year they grew beautifully but last year they barely grew at all despite me feeding them regularly. I hadn't changed the compost from the previous year. Should the compost be replaced every year? I hope not, got about 30 pots! Will cost me a fortune!!
I would agree, i gave up on everything in my garden by july last year.
However, i always use old compost for my tubs. I just add whatever i can...this year will be mushroom compost but i always add a handful of growmore to each tub and mix it up well.