Question
My landscaper wants to put an oil spray on our arborvitae.  He also wants to
spray all of our shrubs with an oil spray to kill insects.  I know there is an oil
spray for the insects, but is there an oil spray that will make the arborvitae a
nice healthy green color?  He says there is an oil spray to make them look
healthier and a bit greener.

Answer
Sandra,

Actually unless the oil is mixed at a low rate, the oil could damage the Arborvitae, and depending on the other plants, there could also be some concens. If you have any plants that are blue (ie blue spruce) or junipers, then there could also be damage to these.

If he insists on spraying, it would need to be a very light mist at a 1% rate of oil with a wide pattern. This will not damage the plants and it should give a small measure of control for any mites or scale problems.

As far as the oil making them greener, this will not happen unless he is mixing in liquid iron. I do not recommend this type of application since too much iron can cause foliage burn.

Good luck,
Ed Gulliksen