Arborvitae is not growing and has brown areas
I have a row of arborvitaes and one of them is substantially shorter than the others. They are about 3-4 years old and this one has not grown as well as all the others on either side of it. It has brown or dead areas on it as well, which is worse in the back of the bush. What is causing this and how can I fix it? Some of the other arborvitaes also have some brown spots, but they are small patches. Please see the attached pictures. Thank you in advance for your help.
Oakland County Michigan
These shrubs are overcrowded and the smallest one is ‘losing the battle’ in the root zone. On its own it will never catch up to the others.
You can try a couple things-
Fertilize and water so that all have ideal growing conditions. Clip back the larger shrubs as the smaller one grows, and over 4-6 years it may catch up.
Or, replace the shrub- a difficult thing to do in that tight space, and can be risky to the roots of the neighboring shrubs.
Or, remove the shrub and allow the neighboring ones to grow into the space. A certified arborist can be consulted to help decide which approach would be most successful. You can find them here by zip code- www.treesaregood.org
The browning can be caused by dryness, or some fungal disease such as phomopsis or other tip blight, or possibly an insect such as one of the leafminers. Also, examining the base of the main stems may show some gnawing damage caused by rabbit, chipmunk or other rodents; damage will show above as browning needles.
Prune off all brown areas and discard in the trash.
If you want a positive I.D., clip a couple branches which include green and brown needles and submit to MSU Plant Diagnostic lab. They can diagnose fungal and insect issues. There is a fee of $20-25. The form, instructions and fee schedule are here- https://pestid.msu.edu
I hope this is of some help. Thank you for using our service.
Thank you very much for your response. Can you please let me know what kind of fertilizer I should use? How much and how often? I would also like to cut the tops of the bushes down since they are too tall. Can I just go ahead and cut off the top or is there a preferred method of doing this?
It is too late to fertilize this year. Fertilize once per year in spring when ground has thawed. A granular slow release fertilizer is best. Without a soil test, there is no way to precisely fertilize. However, products labelled for trees and shrubs will have a recommendation on the label, so, follow that if you don’t have a soil test. A granular slow release tree/shrub fertilizer with an analysis of 11-7-7 or 4-3-4 are two examples.
You can prune and shape the top if you don’t cut into bare wood. Bare wood on the shrub may not have dormant buds to leaf back out, leaving a bare spot. Take no more than 1/3 of total greenery off in any one season.
It is getting late to prune. Pruning now could generate fresh growth that may die over winter because it may not be hardened off enough by this fall. If we have a long, warm fall then pruning now may work- you can see that this is somewhat of a gamble at this point. It is best to prune in spring before new growth, or in late spring to early summer after the initial growth has come out. If you prune now, watch for some dieback next spring in those areas and prune it off. Always use sharp clean pruning tools. Ragged cuts do not callus over as quickly and can let disease in.
Here are links on pruning shrub evergreens. I am giving you a couple of video links that may have some advertising attached—- MSU Extension doesn’t endorse or recommend any retailers or products by name, these videos are linked here only for their instructional content.