Imagine a soil drench.......1 Teaspoon (5 ml.) to a quart (Liter) of water is the usual recommendation... as a "Soil Drench."
A few drops of liquid dish soap to emulsify the solution.

If using Soil/Organics and biological activity is still desired, do not use dishsoaps labeled antibacterial as they contain the chemical "Triclosan" which is very effective as an anti-bacterial, anti-Fungal agent)

Research has shown that neem has some systemic action in plants, meaning that the plants absorb it. When applied...to soils, neem can be taken up by the roots of some plants and translocated to other parts of the plant. Neem may remain active in the soil up to four weeks, depending on soil conditions.

When neem is applied to plant foliage, its systemic action is limited??new foliage must be sprayed periodically for adequate protection.