We are happy to look at photos (if you attached them already, we did not receive them), though plants that have been dead for a length of time are harder to diagnose, since symptoms either disappear or are muddied by secondary issues. The shrub with only partial dieback may be more informative. A common cause of failure of Japanese Holly in our area is a fungal disease called black root rot (Thielaviopsis). This pathogen can impact a range of unrelated plants, including flowering annuals in addition to other species of holly.

Infection is favored by poorly-drained or frequently-wet soil and cooler soil temperatures, so it may have set-in during spring or a prior season. Evergreens are known to sometimes take awhile to manifest symptoms, even for serious damage (such as that which cuts off the water supply between roots and foliage). There's more information about this disease in this publication: https://plantpathology.ca.uky.edu/files/ppfs-or-w-03.pdf

Have any conditions changed in recent years or months that may have stressed the hollies? This could be redirected moisture from grade changes or downspout relocation, increasing soil pH due to concrete leaching (or perhaps runoff from a limed lawn), or heavy fertilization (also potentially from lawn runoff combined with any applied to the hollies themselves). If they're regularly irrigated, was the pattern of watering changed? Was there any digging in the root zone, either for construction/repairs or installing nearby plants?

Do you notice any signs of gnawing or missing bark at the stem's base, near where the soil surface was? Voles are sometimes the culprit in relatively sudden shrub death, as their feeding on sapwood deprives the foliage of moisture and nourishment.

You should be able to attach image files to this reply, and if you need to share more than three (the system's limit), simply reply more than once to send additional pictures.

Miri

Dear Miri,

Thank you for your prompt and detailed reply.

Hopefully the attached pictures are helpful.

The roots seem OK on the “dead” one which seems to be trying to grow a healthy branch. Is the black root rot a readily visible disease?

Several months ago we did put in a new asphalt driveway adjacent to the bushes which they slightly regraded but mostly to flow away from the bushes/house.

In addition, we did have our grass treated with lime last fall which we do not do very often. We have minimal lawn service to control weeds and fertilize.

The bushes get watered with ½ in. Rain Dripper with ports spaced about 12 inches apart in the summer when it is hot and we go on vacation for some weeks. Otherwise when I am home I turn off the automatic water when we get enough rain.

There is no indication of vole damage.

It looks like the bush went into some sort of shock as we walk by the bush in our front yard daily and one day we noticed the all the leaves on the middle bush was brown. The bush next to the driveway is browning slowly is about ½ gone.

From your response I am inclined to think it is a damp-soil issue.

My question is: can I replace these bushes with the same type of plant or is the fungus in the soil?

I can raise the bed slightly but do not want run-off going towards the house nor the sidewalk.

What amendments would you recommend?

I know I should plant high and not deep.

I would appreciate any suggestions.

Diane

Hello Diane,

Thank you for the photos. We cannot determine the exact cause of death from the images (both because they're a bit small and, mainly, because the plant is too far gone), but the root system is definitely undersized for a plant with this amount of top growth. There should be a lot of fine roots growing off of the thicker roots, akin to twigs coming off of larger branches. This implies that they rotted away and caused the death of the branches, but it's also possible they disappeared  (due to secondary rot) after the shrub was already dead. The small stem of green growth is not necessarily a good sign; most likely, it just hasn't died yet. The plant which is half-dead/dying probably won't recover and should also be replaced.

Black root rot is somewhat visible in that the recently-dead or dying roots would have a stained color and be easy to pull apart (usually with root rots, the outer sheath of the root pulls off of the stringy inner core with a slight tug, rather than snapping in two). Confirmation of that particular pathogen would probably need to be made under a microscope, though, which is not something nurseries or most landscape companies would be able to do. It's such a common ailment, though, and an organism fairly ubiquitous to soils in our area, that doing lab analysis it not very practical or cost-effective.

As with most plant infections, the three key points on the "disease triangle" that permits the development of disease are: (1) having the pathogen present in the environment, (2) having a vulnerable host plant, and (3) having conditions suitable for infection. Eliminating the pathogen is not practical or achievable in this case, so minimizing host plant susceptibility (by reducing stress from its growing conditions) and impacting what environmental conditions you can (mainly via irrigation choices and siting the plants where they have room to grow) are the methods by which you can break that triangle. Without all three conditions aligning, diseases won't be an issue.

You can try again with Japanese holly if you prefer (especially since few alternative shrubs will closely match its look). The plants appear to be confined to a smaller space then they'd prefer with regards to their potential for growth, but that may not be something you can alter at this point. One of the smallest-growing Japanese holly varieties is 'Soft Touch', which matures around two feet high and three feet wide, and therefore would require the least intervention for size control. Trimming is well-tolerated by hollies, but reduction of a plant's size by a significant proportion when compared with its mature potential can cause it chronic stress. (Granted, bonsai are treated this way and can live very long lives, but they are also meticulously monitored and somewhat pampered in other ways.)

The likely greater issue is one of soil moisture and drainage, so yes, amending the soil a bit upon planting may help with this to some extent. Compost is useful for this, but be sure not to add excessive amounts - you only want to "fluff-up" the soil a bit while not creating a markedly different zone of two distinct soil types, as, ironically, this might interfere with drainage. Mix in whatever amount you use well.

Loosen the roots on the new plants well before planting, as leaving them matted in the shape of the pot can delay or prevent establishment. Try to keep plants at the same level they were growing in the pot; in other words, don't plant too high or the exposed roots can desiccate before the soil settles. If mulch is used, keep it a few inches away from the crown (where stems emerge from the soil).

Going forward, you may need to more closely monitor and adjust the irrigation system. We can't say how long it would need to be run to adequately soak the root zone, so check it after at least an hour or two and feel how far down the soil has been moistened. Your goal should be several inches. How often the system will need running depends on weather and how well the soil retains moisture; feel the soil around five inches deep (not including any mulch) and water well when it's drying to that depth. As a rough guideline, most gardens that use sprinklers tend to need to water once a week during hot, dry stretches of weather. (Properties that run their sprinklers daily for only about fifteen minutes or so - commonly a default setting on irrigation systems, it seems - are doing the opposite of what effective irrigation would be, unless they're specifically trying to germinate turfgrass seed.)

The final option is to use different species to replace the hollies, though which candidates are the most appropriate will depend on a range of factors, starting with what conditions in this planting bed seem unsuitable for the hollies (staying too wet, drying too often, etc.).

Miri