I have been using Neem oil for over 7 years and I love it. But I do not use it as a soil drench. I use it monthly as a insect and disease preventative. It is a systemic.
In a gallon pump sprayer I fill it with water. Then add a tbs of Neem and a few drops of dish soap. I spray my orchids up, down, over and under. It smothers bugs on contact. The soap helps it cling to the plant. After a few months my 175 orchids have absorbed it internally.
But in the beginning I sprayed once on say a Saturday. Early in the morning so it dried before the sun hits it. Then I sprayed a second time two weeks later and a third time two weeks after that. I had a horrible False Spider Mite infestation. Those three sprays were meant to smother adults, then kill hatchlings and a third spray for good measure. I would say 95%+ of the bugs died fairly quickly. Once those three base line sprays were made then it just became once a month spraying,
If you skip a month or forget to spray, it is okay. Just get it next month. The plants are fine in the meantime.
