NEVER>> EVER>>> fertilize a conifer ... unless a soil test shows something is lacking .... or that is some big block of limestone ... wonking up the soil ...

interior browning is ENTIRELY NORMAL ... and increased by the usual stressers.. like drought.. transplant ... new driveway .. etc ... and moisture in the last month.. does not really address what occurred the rest of the summer ...

IGNORE it.. before you kill it with too much love ...

it is not a shrub.. it is a conifer ... and there is a conifer forum.. where you might see many posts about interior browning...

good luck

ken

I'm not sure I'd agree with Ken's assessment :-) Standard American arborvitae often do display interior browning - it is simply a manifestation of the interior foliage being shaded out by exterior growth (plus the natural lifespan of healthy foliage) and is entirely common.

However, the threadleaf arborvitae has a very different growth habit that pretty much excludes significant shading of the interior growth, at least to the same extent as the denser, more upright forms. Plus, the plant in the photos is displaying some discoloration on more exterior growth as well, which leads me to believe that there may be some moisture issues involved, most likely a drier than optimum rootball.

Make sure drainage is adequate and the plant is sufficiently hydrated, especially as it enters winter. And not planted too deeply. Fertilizer is not indicated at this time but you may want to consider an all purpose fertilizer in spring as new growth commences. It is unreasonable to assume that any plant never needs fertilizing in a cultivated situation - that is entirely dependent on existing soil conditions, not the the plant itself - although for well-established woody plants, the need for supplemental ferts is typically quite small......that's well-established woody plants.......:-)

btw, a conifer can certainly be considered a shrub. That term - shrub - only refers to a habit or manner of growth, not a botanical classification, and can apply to conifers as well as any other woody plant.

We had two arborvitae in front of our house and our neighbor had a row of them. They started to die from the inside and got so ugly we cut ours down. When my husband cut them down, he noticed what looked like bagworms. Our neighbor's trees started doing this a few years before ours and we figured that it was probably the same problem.

Not saying that is what yours are suffering from, but we just didn't look close enough before to try to treat for the problem.

Vickie