Plant Sarpo varieties now

The trouble with second cropping is that the shoots emerge at a time when late blight is likely to be at its peak. But if varieties have useful resistance, they can struggle through a blight attack and give a good crop of new potatoes in late September/October.

Planting in large containers is a good idea as the plants can be moved to a sheltered location or into a cold greenhouse/polytunnel if the weather turns nasty or frosty.

Seed bought in the Spring for normal cropping can be kept through the early summer in trays or egg boxes exposed to the light.  You can keep them in a cool windowsill indoors or outdoors, again somewhere cool. Watch out for aphids on the sprouts and for hungry rodents.

Seed that is stored this way is physiologically old and that means the plants produced may lack vigour and have a shorter growth period before producing a crop of tubers. It means that maincrop varieties will form a crop within 100 days instead of the usual 120 or 130 days. You can read all about seed age in Steve Johnson's Bulletin (Univ. Maine).  He also explains how you can cut seed into pieces before planting.

I have been planting a batch of Sarpo varieties in containers periodically over the summer and am planting a new batch now.  I prefer to drop single seed tubers into small (1 litre) pots of compost just to start them off.  They should emerge from the compost in a couple of weeks when they can be moved to a larger container.  I use 35 litre pots and set two plants in each.  Plant fairly deeply to avoid greening of new potatoes that poke through the surface of the compost.
One litre pots with one seed potato in each

Repotting the rooted up seed into 35L pots. Dave here is a volunteer and great supporter of Sarvari Research Trust

Pots should be carefully watered - don't let the pots dry out and don't waterlog the compost or you will induce rots.

Experts like Dan Unsworth have refined pot-growing of spuds over the years.  His YouTube videos are really entertaining and show how you can produce very heavy yields of Sarpo potatoes using a variety of composts including his own from his compost heap. He gets 13.4lbs of spuds from a 35L pot in this video. I like his horse whinnying in the background of some of his films.