When evergreen conifers like arborvitae turn brown, they do not recover, and it indicates the plant has died. Frustratingly, sometimes the event that pushed them over the edge of their stress tolerance (or an injury to the main stem, if that was the cause), occurred weeks or even months prior to the start of browning. This slow-to-dry trait is one reason cut conifer foliage is popular for holiday decorations, like a cut Christmas tree. It does make diagnosis challenging, though, since by the time symptoms of a problem appear, it may be too late to determine what the cause was.

Arborvitae roots are sensitive to staying too wet, and must be planted in soils that drain well. They similarly don't want to dry out too much, and last year much of Maryland experienced a period of drought (for some areas, this lasted just about all season). Was the plant installed last year, or several years ago? If so, was it monitored for watering needs periodically when rains were sparse? Feeling the soil about six inches deep and watering once that depth becomes somewhat dry to the touch, is generally the best approach.

Was the arborvitae planted from a container or burlapped root ball ("B&B")? If a container, were the roots loosened well prior to planting? If not, that tangled root ball has trouble establishing, and it can be harder to water them as needed since the interior of the root mass has a very different soil texture and drainage than the soil surrounding it. If it was planted from a burlap ball, was the burlap removed and any twine or wire cage removed as well? If not, that can impede root establishment, and also interfere with determining when to water.

It looks like much surrounding the base of the plant is in place, which is useful to keep a mower or weed-whacker from accidentally hitting the lower bark, which can be a fatal injury. Over-mulching can also bury the trunk bark and make it vulnerable to problems that can kill a tree/shrub, though it doesn't appear that mulch is laid too thickly here. (It's hard to see, but you want only a 2-3 inch deep, flat layer, and not a mound.) When you remove it, you can look for vole chewing on the bark around the soil line, though this doesn't look like a situation where they would be a primary culprit (more information in the linked page).

For the future, we recommend not applying any sort of treatment (insecticide, fungicide, etc.) to a plant without a diagnosis, since they will be ineffective if used for the wrong ailment and may even damage foliage if misapplied. In this case, your neem use and fungicide didn't cause much damage since it was already too late, but neem only affects insects the spray physically contacts (like aphids, leaf-chewing beetle larvae, and caterpillars) and has very limited uses for pathogens. Fungicides are sometimes broad-spectrum (targeting a range of fungal disease spores), but can only help to prevent infection before spores resting on the leaf surface enter the leaf; once that happens and infection has taken place, they have little to no impact on the disease. In cases like this, with drastic and complete dieback, if an infection is responsible, it's likely root-oriented and not in the foliage. Drenching the soil with a fungicide in that case, though, will not solve the problem.

A root rot infection is possible as the reason for the plant's loss. When soil stays too wet, roots don't get enough oxygen and can die off or become infected by opportunistic "root rot" pathogens. These organisms are common in soil but don't cause problems until the host plant is stressed. If soil doesn't drain well, for example, that can set up conditions conducive to infection. We can't say whether the dieback here is root rot related or the opposite (drought or under-watering), because the above-ground symptoms can look much the same. One way to detect if root rot was at least partially responsible is to examine the roots. After removing the plant and shaking off or hosing-off some soil, examine roots for a tell-tale trait: the roots will usually be mushy, where a light tug pulls them apart into two sections, an outer sheath and a stringy inner core. Roots dead from other causes tend not to do this, and it will take more force to break them, they won't be very mushy, and when pulled will snap in two more cleanly.

If you want to try replanting 'Green Giant' arborvitae in that area, now (spring) is a good time to try installing some. Young plants establish faster and catch up in growth to older plants, so resist any temptation to install a larger plant to make up for lost time. Loosen roots from container-grown plants, and don't be alarmed if a few break in the process of disentangling them; that's normal and largely unavoidable. Look for as minimally root-bound (tangled, matted roots on the inside of the pot) a specimen as possible to make planting and acclimation easier on both of you.

The advice you were given about nutrients lacking on a slope is not correct, nor would a nutrient deficiency have caused these symptoms. A laboratory soil test is the only reliable way to determine what levels of major nutrients are present (and the soil acidity, or pH), and you will likely find that many are plentiful or even "excessive" (not a problem needing reduction, but abundant enough that adding more is unnecessary). If you're curious and want to send out a sample for a soil test, the page above describes the process. We can help to interpret test results if desired. Labs can be busy this time of year, so receiving results might take 2-3 weeks.

The holly looks a bit sparse and yellower-green than they usually are, but otherwise fine. Hollies do normally shed some of their older foliage in spring as they prepare to put out new growth. Sometimes excessive shed is caused by either stress (like getting too wet or too dry) or even having had a very productive growth cycle the season or two prior, since it's leaves several years old that the plant is dropping. Some minor leaf spotting developing on those shedding leaves is also normal and not a health concern for the plant. Chinese hollies (what this type appears to be) have above-average drought tolerance for a holly, but similar conditions can stress them, such as not being watered if needed during dry spells while young plants are establishing in their first year or two in the ground, and not having loosened up any tangled/matted roots upon planting. Hollies appreciate acidic soil, so a soil test can reveal if the pH needs adjusting to bring it more in line with what the holly roots need in order to make better use of the existing soil nutrients. If the holly is close enough to the arborvitae (say, within a couple dozen feet) and you don't have reason to believe the soil in this part of the yard varies that much, one soil test would suffice for both plantings. There is no harm other than added cost to doing separate tests, though.

For now, just monitor the holly for watering needs and water only once the soil several inches down has become dry enough to need supplemental moisture.

Miri

Hello Aminata,

Yes, you can replant in the same spot, and if any soil amendment (compost) is still present, mix it thoroughly with the soil so it's blended well as that helps to keep drainage more consistent around the roots. "Young" is relative, but in this case, just avoid planting an arborvitae already 10 feet tall or so...the younger the better in terms of ease of planting and less stress for the plant, but nurseries tend to stock evergreens like this in a limited range of sizes, which is fine. We just wanted to caution you against picking a plant that's too big to start, since they can take much longer to settle-in. You definitely will not have to water daily, just whenever the soil becomes somewhat dry to the touch around five inches deep or so, next to the root ball. The root loosening doesn't have to be super extensive, just enough to disentangle what you can (it doesn't have to be perfect).

Miri