Question
I HAVE 40  EMERALD GREEN ARBORVITAES 4 YRS OLD  LINNING MY DRIVEWAY WITH 3-4 INCHES OF MULCH COVERING THESE   5-6 FOOTERS, AND DOING VERY WELL...I HAVE THEM SPRAYED FOR INSECTS, BUT I FERTILIZE MY SELF WITH HOLLYTONE...I HAVE BEEN FERTILIZING  IN EARLY SPRING  (MAY-JUNE)AND FALL (SEPT.- OCTOBER) DO YOU LIKE HOLLYTONE AND AM I OVER FERTILIZING?I QUESTION THE FALL APPLICATION. ALSO IS THERE ANY SPECIAL CARE FOR THE COLD, SNOWY WINTER SEASON ?  I AM VERY CONFUSED ABOUT THE PRODUCT WILT-PRUF( WHICH I HAVE NEVER USED...SO FAR THEY HAVE HANDLED THE WINTER SEASON USING NOTHING  VERY WELL...THANK YOU

Answer
Arborvitaes benefit from fertilization especially as young plants, but often there are enough nutrients in the soil if planted near lawns which the long shallow roots can extract. You can fertilize once per year with Holly tone (and this would be my very warm recommendation for choice of fertilizer for arborvitaes) but I would not exceed this. If color, growth, and form is ok, you can probably even cut back to every 2nd year.

I do not suggest you fertilize in fall. Arborvitaes are already subject to winter desiccation and the best way to avoid this is to ensure that the tree "hardens off" in late fall. To do this, do not keep watering regularily through first frost. Try to stop watering in late summer and graudally let the tree slow down and adjust. Continuing to water and fertilize will have the opposite effect. I am not saying you should expose the tree to draught stress (if no rain for a very long time you may want to water) but no weekly watering regime, etc.

If you follow above, you will let the trees slow growth and "close down" for the winter. They can usually go through winter then without any big problems.

I like wilt pruf for some plants like azaleas (especially if just transplanted) but I have never had good results with this product on arborvitaes. I would not recommend using it. Instead concentrate on "toughen" up the trees a bit before winter as above.

Winter desiccation occurs when the sun heats the needles and prompts transpiration. Transpiration is like when we sweat except that when soil is frozen, there is no water to pull up from the ground, and the moisture is lost inside the trees. This is particularly a problem in soft tissues and new cells which have not had a chance to harden off before winter.