Humic acid works by complexing metal ions in the soil, holding them in a form roots can take up instead of letting them lock away. It therefore does most on soil that has nutrition the plant cannot reach — and does not replace fertiliser on soil that is simply depleted.
The best moment is just after an organic application and while the soil is moist, so the solution travels down with the water to the fine-root zone. Drenched into dry soil it stays in the surface layer and most of the effect evaporates.
On concentration the rule is dilute and repeated rather than strong and once. Mix to the label — HUMICRIC comes in 1 kg, 10 kg and 25 kg so a smallholding need not buy more than it can use — and water around the drip line, not into the collar.
