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A third of my arborvitae trees died

last year

I had planted around 50 of Thuja Emerald Green Arborvitae (Smaragd) them in the following pattern. I planted them last August 2021. They were all nice and green up until June of 2022.

First one tree died, then 2 , then 3, then 5, finally 15 of them are dead in less than 4 months.


_ _ _ _ _ _ _ _ _ _ _ _ _

| (E) (W) |

| |

Ones in the E and W are doing okay. Half of ones in N dried out completely or they are yellow, about to turn brown.

I installed drip irrigation at the roots of these trees and have been watering them regularly about once a day. The soil type is clay in my area (pacific north west, seattle, wa)

I have attached the root portion of the dead trees. I sprayed insecticide / fungicide combo. I added slow release fertilizer. Nothing seems to recover or slow them down from dying.

Can someone call out what is happening and how can I prevent in the future as I am going to replace the dead ones by 15 new trees.

How I can treat / prepare the soil for the new trees and a recommended procedure for planting, so that I don't end up in same situation again.

started with becoming yellow at first

Root of a dead tree

Root ball

why do i see the tips have some sort of a dried flower ?

The pit

Comments (5)

  • last year
    last modified: last year

    Drip irrigation is insufficient- you have no idea how far down it is penetrating and from the looks of it not nearly deeply enough.

    Don't plant trees in August.

    Wait for cooler weather.

    And when you do plant trees water with a hose on a slow trickle for upwards of 30-45 minutes per tree. Then you dig down and see how deeply the water has penetrated. You do this a time or two until you know your soil better, but they will need deep watering the first year of establishment. Not daily- that's too often. But DEEPLY.

    Don't feed stressed plants or trees, it stresses them further.

    Don't spray fungicide unless you have confirmed a fungal problem.

    Last- when you plant trees- especially mass produced species like this, you need to get into the rootball with your fingers and break it up a bit and ensure that the roots are not tangled, circled, or otherwise a fat mess.

    I'm guessing August planting plus insufficient watering took out your trees.

  • last year
    last modified: last year

    It's your business, but I wouldn't want the front of my house blocked by a solid row of arborvitaes like that.....

  • last year

    note section one ... the trick is to plant in dormancy.. if you can get stock at the proper time.. if not.. plan ahead ...

    i presume you are trying to hide the road your house abuts?????


  • last year

    @Sri Suggest you post your question to the Pacific NW garden topic for replies from folks in your area - you mention Seattle so you’re in Zone 8a/b. You may have moved on & gotten advice locally since you posted 2 months ago but maybe not. I also live in WA & have some thoughts about your issue - which I have to tell you isn’t uncommon when doing a mass planting of these arborvitae or ’Emerald Greens’. I agree with much of what @cearbhaill (zone 6b Eastern Kentucky) told you except for the timing of planting. In our area August is ok as long as you water DEEPLY as was suggested, From the root ball pics you show, the primary & maybe only, issue with the plants was that they died from lack of water. When planted they should’ve been deep watered immediately & then once weekly until our winter rains started. That should’ve been restarted after spring rains stopped but with periodic checking deeply down into soil. We’re running hotter weather these past couple summers so watering is more than it used to be here.. The other thought I want to pass along is that you have way too many of those plants. They should not be any closer than 4’ on center & 5’ is better for plants under 6’ at planting. I promise you they will grow to create a solid green screen - and faster than you think! If they survive the first year, they take off as if on steroids because of our rain - thus the ’Emerald Green’ nic name for our state. I won’t comment on your choice of screening plants as others did but, you might think about adding a planting bed along the house side of your green screen. Add some flowering shrubs & shrublets to create a pretty view from your house. You asked what the dried flower tips were - those were new growth coming on. If the plant had lived, those little dried balls would be bright green new growth. No flowers on those arbs!

  • last year
    last modified: last year

    Whatever caused it the roots in your pictures of the balls are dead. And dead roots = dead tops, sooner or later. While failures of at least part of both new as well as long established hedges of 'Smaragd' are common here in western Washington, due to more than one potential cause the timing of your own problem with this variety may coincide with an abnormal blazing and early hot spell we had during a recent June. With even native wild living conifers near pavement getting scorched by it. And your new planting was near a large area of asphalt. With mostly bare dirt between it and the road.