That looks like a pH issue to me. If it is, adding nutes won't help and could actually make it worse. I'm also wondering that since it's outdoors and the weather is still generally cool if the soil isn't staying too wet and possibly effecting the roots ability to uptake nutes. I put 3 plants outdoors early this year, in pots, and they aren't drying out at all. They have been outdoors for almost 4 weeks now and I've not had to water them once. I'm seeing pH related issues on them from the roots staying wet all the time.