yellow

I haven't been having much luck with cucumber seedlings. As soon as they get their third true leaf they start to yellow and die. I have tried two different brands and have tried jiffy pots, jiffy peat pots and direct to soil. Any ideas? I live in Bundy, subtropical climate. Thanks in advance.

Leaf #2 by Jarrett posted Apr 14, 2017 at 1:23 PMPlant #2 by Jarrett posted Apr 14, 2017 at 1:23 PMPlant #1 by Jarrett posted Apr 14, 2017 at 1:23 PMPlant #3 by Jarrett posted Apr 14, 2017 at 1:22 PMLeaf #1 by Jarrett posted Apr 14, 2017 at 1:22 PMLeaf #3 by Jarrett posted Apr 14, 2017 at 1:23...