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.

So far, so good. The Blight pathogen is slumbering

So far this has been a lousy summer - at least here in N. Wales. Yet there have been very few reports of blight in potato crops in UK.  So far, according to the Potato Council (now called AHDB Potatoes) website there is blight in 4 crops in Scotland, 4 in England and just 1 in Wales.  Undoubtedly, there must be more than this as lots of outbreaks remain unreported.

What is clear is that the amount of blight reported is a whole lot less than in any other year recently. Usually, by this time, blight has been seen most areas of the country and some crops are severely infected. Why can this be?

We certainly have had lots of dry weather that does not suit the pathogen and this has been combined with cold nights. Blight does not multiply and spread in these conditions.  However some districts have had Smith Periods (warm and moist), conducive to blight but the organism has not been around to take advantage and growers there have been lucky so far.

But we should not be complacent. We still have August and September left in the growing season and plenty of opportunity for blight to appear in force to cause havoc particularly in the maturing tubers. If the new potatoes get infected, they will not store and could start to rot soon after harvest. You can check on the incidence of blight in your area and the recent weather conditions here

A good method for controlling blight in a susceptible variety is to treat the crop with a liquid containing phosphite (phosphonate).  A product like Phi-Diamond produced by Emerald Crop Science showed good control when we used it in 2013. It controlled foliage blight and treated crops gave a good yield advantage. Phosphite is thought to act by stimulating the natural resistance mechanisms in the potato and is a benign chemical compared with other biocidal chemicals and a whole lot safer to use than the heavy metal poison that is copper.