Planting potatoes in old compost | How to rejuvenate old potting compost

We are late with our first planting of potatoes this year. Usually we start in early February and get our first harvest towards the end of April. This year we should get the first crop towards the end of May. Once again I am planting up 15 litre pots along with a few 25 litre pots - good sizes for first earlies. I am reusing some old potting soil and rejuvenating it by adding some fresh organic matter and some feed.