Is neem oil harmful to butterflies , bees, or hummingbirds? Will they avoid plants treated with it? Will it keep deer from eating plants treated with it? I am planting a garden to attract butterflies, bees, and hummingbirds.
Baltimore County Maryland
Yours is a very good question. We typically recommend Neem oil or its derivative, Azadirachtin, as a safer alternative than some of the other residual insecticides, and we also recommend it as a repellent against some of the more difficult insect pests such as Japanese Beetles.
It is quite possible that Neem will repel many of the insects and birds that you wish to attract, but on the other hand, if used correctly, it should not be harmful to any of them.
There is no evidence that Neem oil will repel deer.
Having said all that, it would be helpful to know why you are interested in using Neem oil. If you are attempting to kill or repel insect pests, it would be much more useful to know the pests and then select the least lethal method of control.
The National Pesticide Information Center has an informative publication about Neem oil. http://npic.orst.edu/factsheets/neemgen.html
For additional information about insect control, you may find some useful tips on our website: http://extension.umd.edu/hgic/insects-annuals-bulbs-groundcovers-perennials-and-vines