Advice needed on purple leaved tomatoes

[Angeldon]

I have 12 tomato plants in an outdoor bed, 6 Ferline and 6 Super Marmande and all the plants have been growing strongly and flowering well. However, I noticed this afternoon that the underside of all the Ferline's leaves are turning purple but the SM's are green and healthy. I've been feeding all the plants once a week with comfrey feed. I know this can be a sign of potash deficiency but am baffled as to why it is only affecting one variety when they are growing under exactly the same conditions.

[Penellype]

What was the temperature where you are last night? Some places were quite chilly, and tomatoes can go purple if they are cold. Some varieties are more susceptible than others. I haven't grown either of your varieties so I can't be sure, but it would make more sense than magnesium deficiency, which tends to affect lower leaves first and makes them blotchily purple rather than just the undersides. You may find the stems have a purple tinge too.

[Angeldon]

Thanks Penellype, I think you've cracked it - the night temperatures here over the past few days have been extreme to say the least - one night warm and balmy, the next quite chilly for July. Looking at the plants again, most of the bottom leaves are still green so I suppose they're more protected. I'll have to choose a hardier variety next year.

[bario1]

I hate to be British and rant about the weather, but I'm so sick of seeing temperatures of 6, 7, 8 degrees at night - no wonder everything is way behind where it was last year. Nothing's being given a chance to thrive! I mean, I know i'm in Scotland but... IT'S MID JULY!!

Rant over.

[Penellype]

To be frank, I don't think this is going to improve in a hurry. The upper air temperatures look set to hold at about 5 degrees below average for around the next 10 days or so, and there is no sign of any real warmth.

In my (untrained but interested) opinion, the culprit can be seen on this map:



from Current Operational SST Anomaly Charts - Office of Satellite and Product Operations

This is a map of sea surface temperature ANOMALIES - ie the difference from average, as at 7th July. Although the sea around the UK is reasonably near normal, there is a huge pool of deep blue to the east of North America. This is exactly where our weather is coming from, and that is (in my opinion) why it is colder than normal. This has been getting slowly worse over the past few months and this latest chart is the coldest I have seen. This may or may not have anything to do with the developing El Nino, which can be seen as the dark orange streak to the west of South America, along the equator.

Sorry to be the bearer of bad news

[bario1]

Whatever happened to the Gulf Stream?

[Penellype]

Its still there, it won't show up on an anomalies map because its not an anomaly.

[bario1]

Of course. As long as it's still there!

[Penellype]

We would be in serious trouble if it wasn't, and that is one possible consequence of climate change that doesn't bear thinking about. The gulf stream is part of a global system of ocean currents which keep the water circulating not only on the surface but also vertically, and it is this which supports life in the seas, keeping the deeper water oxygenated. Without the currents the oceans would become stagnant and virtually lifeless. It has happened before.