Quinces, I would just use it at normal concentration exactly as you were planning to use the usual one without the addition of sequestered iron. Processed seaweed has a low salt content that will do no harm to the vast majority of plants. You would have to seriously overuse it to cause a problem and even then, any excess salts are highly soluble and will leach away rapidly. Same with the extra iron, it’s rarely a massive quantity in these liquid feeds to cause any harm and will help particularly in alkaline soils where plant take-up of iron is inhibited by the high pH.
Many rose growers including me use Vitax Azalea food (theoretically only for acid lovers) but exactly the same formula as the old David Austin food, designed for all garden soils. I also add powdered sequestered iron, which is far stronger, to counteract leaf chlorosis caused by my alkaline soil and you do have to be careful not to overdose with that.
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
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Many rose growers including me use Vitax Azalea food (theoretically only for acid lovers) but exactly the same formula as the old David Austin food, designed for all garden soils. I also add powdered sequestered iron, which is far stronger, to counteract leaf chlorosis caused by my alkaline soil and you do have to be careful not to overdose with that.
PS. I have now googled this and will look out for products and read the packs.
"Have nothing in your garden that you don't know to be useful, or believe to be beautiful."