My boxwoods have a yellow leaf edge. Deficiency?

Boxwoods planted last spring in a shallow trench now have a distinct yellow leaf border.
Wondering if this is a nutrient deficiency? Or symptom of something else?
Any feedback would be appreciated

The variety is Buxus 'Green Gem'

 

Funny, I have 2 boxwoods given to me that look the same. I just assumed that was characteristic of whatever variety they are . . . really quite pretty.

 

Doesn't seem to be any of the usual culprits affecting Buxus from what I've researched. There are yellow-leaf-margined cultivars, but I suspect that isn't what is occurring here.

 

Possibly too much water? Mine look similar right now, and they’ve been solid green ever since they were planted five years ago.

 

I'm so interested to see this question and the comment that ones looking like this did not start out that way. I photographed a planting last summer that I was wondering about. They look so pretty like this.

 

This looks like winter chlorosis, a not uncommon phenomenon in the cool, maritime west of Canada and Pacific Northwest of the US. It is hard to diagnose precisely, but a variety of issues could be the cause. It is most common where roots have been damaged (e.g., from drought, drowning, disease, dog pee, etc.), and in cold, strongly acidic, nutrient-deficient, compacted or water-logged soils. Manganese toxicity, which is common in the winter in manufactured soils (especially when there is a high bark content), can look like this. It is usually most severe when soil iron and especially nitrogen are in short supply (as is common in winter). The chlorosis usually disappears when the weather warms in June.

 

I would not argue against the effects of winter chlorosis but, with my boxwoods, this is a year-round appearance. Even the tight new buds show yellow tips before they begin to unfurl. I read on Pests and diseases - Buxuscare.com that "Boxwood is a plant that needs a lot of nutrients to stay green. When the plant has received too little fertilizer, the plant will grow unsatisfactorily and the leaves will become a pale yellow with yellow edges." Since the leaves on my plants are a nice dark green with only the tips being yellow, I don't think more fertilizer would change that. I should mention that they are grown in pots and seem otherwise healthy. To me, the yellow tips give the plants a lively appearance which I like.

PS I found Dougas Justice's comment about Manganese toxicity very interesting because that may explain why a few other plants in my garden - especially rhododendrons - go so yellow in the late fall and winter. Thank you for that.

July 12, 2018 Followup:
The new leaves on my boxwoods are now unfurling a solid, dark green. I attribute this to the sprinkling of ammonium sulphate I gave them at the beginning of June. Apparently the slow-release fertilizers I had used in previous years did not supply enough nitrogen.

 

For anyone who may still be interested in this, the yellow edge on my boxwoods' leaves disappeared after I sprinkled some slow-release fertilizer and bit of fast-acting ammonium sulphate under them (they are in containers). The leaves are solid green now and larger than last year's leaves.

 

@Margot, I hope you're not missing your pretty leaf margins. Thanks for posting the results of your test. Can you edit your earlier posting and replace the photo? Or am I the only person not seeing it?

 

July 12, 2018 Followup:
The new leaves on my boxwoods are now unfurling a solid, dark green. I attribute this to the sprinkling of ammonium sulphate I gave them at the beginning of June. Apparently the slow-release fertilizers I had used in previous years did not supply enough nitrogen.