Im putting in some plants-violas etc - inot pots on my patio. How often should I replace the compost or can I just top it up when required? I also have a large bag of compost in my garden box which has been open for a year or more. Is it OK to use that?
In a big tub, i usually change 25% each may time. I mix the new compost with the existing old stuff and add either growmore or fish. blood and bone as mentioned above. Mix the fertilizer in well.