When I see yellow, I usually think nitrogen deficiency, especially if it is starting in the lower leaves. Nitrogen deficiency can be present early in the season due to low temps, as the soil organisms aren't up to speed in decomposing the organic matter that is present.I usually give my plants a drink of fish emulsion which corrects it fairly quickly, but as I don't put it through my drip system, can be fairly labor intensive. If you are worried about pH, you can quickly check that with a home soil kit, or through your extension office. Good luck- diagnosing plant maladies can be a challenge sometimes.

We have found exactly what you describe, and, usually suspect phosphorus deficiency. With the low temperatures and lack of sunlight, we had this problem with one variety of Karma dahlias in the unheated hoophouse. The other nine varieties of Karma dahlias were not affected. The pH of our soil here in Michigan is fairly neutral. The use of fish emulsion is a very good idea indeed.

Thanks guys- as it happens that was in my head as my next line of attack: fish emulsion. There are only 30 to 40 plants or so, doing it by hand should be easy (I did about 300 strawberry plants by hand yesterday)

Thanks,

Kristne

An iron deficiency might still be involved, as it seems quite common in alkaline soils. In the desert where I used to live, people commonly used Ironite. But a friend of my brother's says he uses the fine shreds that brake repair places have as waste when they grind something in the wheel (?) to smooth it. He said it doesn't have the bad stuff that Ironite does (I don't know what that is).

Sue