Golden deodar tree
I have 4 golden deodars. They took a real hit in the Boise winter. Two losing all needles, two partial loss of needles. We had them planted as established trees 5 years ago. A local nursery suggested treating with Thrive and heavy watering. Having done this, the partial trees have regained some needles. The barren trees have regained 25% . My question is.....the ones that are barren, with flexible branches and a few new needles.....do I just give up and have them taken out ? Is there any other treatment to save these trees? Thank you.
There is not a lot you can do except continue with ample water management, wait and see. If the trees don't recover fully and develop a full foliar canopy by the end of August, I would expect them to to be even more susceptible to sub-zero temperatures this coming winter.
Soil fertility and plant nutritional support is important, but I would avoid repeated use of Thrive liquid fertilizer, primarily because or the Potassium chloride content, which can be detrimental to soil chemistry and soil biological activity. Thrive product information states that it is designed for aquatic plants. Go with a natural source complete organic fertilizer like 'Down To Earth' - All Purpose.
Boise is primarily zone 6 I believe, which is the coldest extreme for deodar cedar cold tolerance. Repeated winters with colder than 0 to -10 degrees F will make it hard for the trees to survive.