Four and a half years ago, we planted 22 Emerald Cedars in a row, approx. 30″ apart.
Until this year, they have done quite well and have more than doubled in height (10′) and width.
Even though I’m on a shallow well, I have always watered periodically right into the fall. Also, I have fertilized every year with Nutrite 14-7-14, except for last year.
This year, two in the center of the row died and it looks like a third (next to the dead ones) is on its way out.
I know we had a bad winter (I live in a rural area on Scugog Island) but the ones I lost were more protected than the others, such as those on the ends.
A couple of months ago, I noticed in the adjacent field, several young black walnuts, some of which were growing about 4′ from the two cedars that died. Thinking they might be depriving the cedars of nourishment, I cut them down, drilled some holes in the stumps, and poured RoundUp into the holes.
I’m concerned about the remaining cedars, some of which seem fine but others which seem to be shrinking in height. This is what happened to the two that died and appears to be happening to the third which is failing.
Could you please advise whether the cause is due to:
1- the winter,
2- the fact that I did not fertilize last year,
3- their proximity to the walnuts, or
4- perhaps they are too close to each other.
5- have I made things worse by applying RoundUp to the nearby walnut stumps?
I am about to do the final application of Nutrite but will wait to hear from you in case this is not advisable.
Thank you for contacting the Toronto Master Gardeners with your inquiry.
Walnut trees produce a chemical called juglone, which inhibits the growth of many other plants by depriving them of the energy to grow well. Symptoms of walnut toxicity range from stunting of growth, to partial or total wilting, to death of the affected plant. The toxic reaction often occurs quickly where sensitive plants can go from healthy to dead within one or two days. Many alarmed gardeners often believe the cause of wilting is due to fungal or bacterial disease. Once wilting begins, the effect cannot be reversed. The severity of the toxic symptoms can vary depending on the plant species that is in contact with the juglone. However, according to the Morten Arboretum Arborvitae (Thuja spp.) are tolerant of walnut toxicity.
Glycophosphates the main componet of Round Up in general will not harm a tree that is a considerable distance away, as long as you didn’t spray during a windstorm or on a really sunny hot day. You CAN get enough drift during a moderately windy day for the overspray to go far if you aren’t uber careful about where you are spraying.
You did not mention if you noticed any pests on your cedars. Cedars can be affected by bagworm, leaf miner, spider mites. Check in between the leaves of your cedars. Cedars grow best in full sun (6 hrs direct light daily), or partial sun/shade (4-6 hrs light daily) in moist well-drained alkaline soil.
Cedars are susceptible to strong winds, snow and ice damage. The mild temperatures we experienced in February followed by the severe ice storm we had in April is most likely the reason your cedars have turned brown. I have a boxwood hedge which was totally brown from wind/sun burn this spring. This is the first time in 20 years that I have had this issue with my boxwood hedge. I did fertilize the hedge in the spring with a high nitrogen fertilizer, 30-10-10 and added a couple of inches of compost, it has thankfully recovered.
Emerald cedars should be fertilized three times during the growing season: May, June, and July. Refrain from fertilizing the hedge in late summer, as the hedge will require rest for dormancy during the winter. However, it is recommended that you apply a slow-release nitrogen and phosphorus fertilizer in the late fall as a hedge “health boost” for spring. Here is a detailed discussion of fertilizers for emerald cedar hedges from one of our previous posts: https://www.torontomastergardeners.ca/askagardener/fertilizing-emerald-cedar-trees/ This post itself contains other useful links.
Emerald cedars have been the topic of many questions for the Toronto Master Gardeners. If you wish, you could search on our “Ask a Master Gardener” website using “emerald cedar”, and you’ll find all kinds of useful information about this popular hedging evergreen.
Good Luck with your cedars