potato help

The plant looks pretty good in the photo but...... some of the lower leaves seem a little crinkled.

A daft suggestion I expect but are there any greenfly quietly munching away in the warmth of your greenhouse?

Or... are the plants too damp?

Perhaps you could try upping the daytime ventilation and see if that helps.

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Someone more knowledgable will come along soon I'm sure. 

I  may well be wrong about the greenflitters....... but it's worth a quick look. 

It's probably too hot for them
Also, you can over water if you don't have good drainage

It could be either of those..... but the lack of drainage is perhaps more likely as, at this time of year, not many greenhouses reach summer temperatures unless they get sun through out the day and no ventilation at all.

Another couple of good ideas worth investigating.