mf the soil is definetly well drained it comprises of grit sand50 %, granite dust 30 % and manure 30 %
vic i'm unsure what u mean by dead strike if u r referring to the yellowing of the bark then about 4 yearsish this is why i chose it over it's neighbours when thinning out a customers hedge i thought it might make a good feature but now i don't really like it.
it seems to have stopped or at least slowed down and their is a small new green shoot just where the die back begins i may just chop at that point and hope it doesn't happen again.
I seem to have unexplainable die back on boxwoods. Sometimes they're are quite vigorous and at other times they seem to have forgotten how to grow, and the twig-like branches lose their leaves and finally die.
Despite that, I continue working with boxwoods. I like their bark and shape.
Donkey, How long have you been growing bonsai in 30% manure. I'm not claiming to be an expert, but that would be my guess why your tree is dying. Your other ingredients, sand and dust is also a concern to me.
I've been experimenting with various mixes both the sand and granite dust (dust being misleading it is v small sharp flakes) are horticultural grade and are sold for drainage purposes. 30% manure is just a guess i give my trees a top dressing of the stuff every year for added nitrogen at the start of the season and they all seem to love it.
Your issue is mostly likely with the manure and possibly the granite dust. Manure, even composted manure, breaks down into extremely fine particles. Those particles can clog any drainage you've got. It can also be EXTREMELY difficult to re-wet after drying out once. It will actually shed water without rehydrating--unless you soak the pot underwater for an hour--which of course, will only worsen the drainage issue, as the manure holds onto water.
Granite dust, especially flakes with flattish sides, compacts. Granite dust is used as a compaction layer underneath paver stones. It serves to drain water from underneath pathways and such. IT IS MILLED TO compact easily--not what you want in a bonsai soil. If you use granite or other crushed stone, the granules must be irregular in shape (not flakes, which suggests flattened sides) so they cannot fit snugly against surrounding particles.
Since boxwood like very well drained soil, but are also prone to die back if their roots dry out, I'd re-think the manure entirely. It's got too many things that make it difficult to manage effectively in a soil mix. I'd also switch to crushed granite or flint used for poultry consumption. That's what we use here in the States.
For the last ten years or more, I've been keeping boxwood in soils that have only 10-20 percent SIFTED GRANULAR organic components (like composted pine bark mulch, or baby orchid mix--fine fir bark), and 80 percent soil-less ingredients like crushed granite, haydite or even turface.
Here's picture of one of my boxwoods. I don't know if the detail is fine enough to see the soil, but it's pretty coarse and granular, primarily haydite with some large particle swimming pool filter sand--which is crushed quartz and not really "sand". Also note the shallower pot. Boxwood can be grown in shallower containers. Deep pots--and yours is a bit deep--can make overwatering issues a bit worse, since they tend to hold onto more moisture.
Additionally, boxwood can tolerate lower pH levels, but can slow considerably, or develop issues with soil that's too acidic. ...I've used a sprinkling of garden lime on occasion to perk up boxwoods that are sulking. Manure is pretty low in pH. A soil that's 1/3 or so manure is bound to be pretty low pH.
Looking more closely at your pic, I think I see what is a classic sign of a boxwood in wet soil--what appear to be reddish dropping leaves. That's a tell tale sign--for me at least--that the soil is staying way too wet for root development and health. I had similar issues with a recently-acquired boxwood that was planted in soil that was too fine and a pot that was far too deep. It had partially red leaves, dropping dead red and brown leaves all over the plant. It also had die back on the twigs. I repotted it into my boxwood mix and a shallower pot. It stopped dropping leaves and pushed new growth in a couple of weeks after that.
I am very new to bonsai...but love and have lots of boxwoods. I would ask when it was re-potted last. Did you sift all of your soil? It may be a drainage problem, does the plant have any ants on it?. Unless you have scorching heat....you could pull from the pot and take a look and look for any buys or powder. Some one answered with a 80-90 percent inorganic. That is what i used with a little clay and water every 4 days....But my plants get morning sun and afternoon shade.
it was only potted last year. and the drainage was ok i think rockm has got it with the thing about the flakes compacting due to being flat sided. should i just water less for now and repot in a better mix next year.