CSI: Milwaukee – Browning Evergreens

What happened to the evergreens? The last three weeks I have been on assignment. I am leading an important investigation for Johnson’s Nursery on browning evergreens. Why are they brown??? Who or what caused this death of foliage? How could this happen? What was involved? Was there in fact wrong doing in this case? Was there intent to kill or be killed? Did the sun, snow, and cold temperatures conspire to destroy life? This Plant Talk will be a report of my findings based on the use of the latest forensics methods that I know of, namely looking at the plants from my truck window and then jumping out and closely inspecting the victims.

I first began noticing something was wrong in mid-March. The yews were brown. Little did I know that a month later other casualties would show up. Chamacyparis, Scots Pine, Vanderwolf’s Pyramid Pine, Douglas Fir, Concolor Fir, ‘Mucronuta’ Norway Spruce, and Alberta Spruce. The last plant to reveal its damage were the Junipers. Various cultivars of Upright Junipers were scorched. Even the native ones along the sides of the roads in our area showed damage.

Concolor Fir were severely burned here, at Johnson’s Nursery.

I have been a CSI plant evaluator for over 34 years. 2014’s browning evergreens is the most extensive damage I have ever seen in our area. In order to make a determination of cause of death or damage I must analyze the evidence.

I scanned the weather records for our area, starting in September and going through the winter. The weather can have a profound effect on the condition of plants going into winter. So what happened? In September, it was dry. We had one half the normal precipitation. This lead to a later than normal shutdown for numerous plants because above average rains in October kept certain plants active. Warm temperatures and good moisture levels in early November didn’t help matters. In late November and December we had a quick onset of cold that quickly stopped any active plant processes and was shortly followed by below zero temperatures just after Christmas. Some of the evergreens were perfectly set up to be hurt. They hadn’t hardened sufficiently. In addition, the winter was very dry. We didn’t have the typical heavy wet snows typically associated with Wisconsin. Almost all the snowfalls were light fluffy ones, demonstrating the drier, colder condition we had. We had an above normal snowfall measurement with below normal precipitation, meaning snow melted down didn’t amount to normal. I wonder whether the fact that the snow was so dry with few melting events that plants had less opportunity to absorb moisture through their foliage like they would in a normal winter. I haven’t ever heard of this method of water absorption discussed as it relates to winter desiccation (water lost from the foliage) of evergreens. I suspect it does occur.

In any investigation the victims themselves provide a wealth of evidence as to what happened to them. Let’s look at the specific groups of plants that had some severe damage.

Japanese Yews – Taxus

These are perhaps the most noticeable of the browning evergreens this winter. It seems that the south and southwest sides of most Japanese yews in our area were brown this spring. In fact, I have seen plants on other exposures looking bad as well though most plants that were sited on north or east exposures suffered minimal damage in comparison. My explanation for this is that the sun hits the south side of the plant for the longest period of time. It warms the foliage and along with the wind draws water from the plant into the air. The warmer the temperature of the foliage the more water is lost. In addition, the drier the air the more prone to drying the plant is. When the ground is frozen a plant can no longer replenish its water resource in its foliage via the vascular system including the roots. Everything is frozen both in the ground and the plant itself. So the foliage that is most exposed to these conditions dies. That would be the outermost leaves on the outsides of the plants where the conditions are the worst—the south and southwest sides.

Image caption. Left: Exposure played a big role in how much damage plants incurred. Above is a spreading yew hedge with an east exposure to the left and a south exposure to the right. Right: The overhang from building caused a water deficit on the side of the plants nearest the building. That side burned.

Our display beds had browning evergreens on the plant’s east side but not the west even though it is shaded by a building. Browning evergreens in this case is due to the overhang from the roof keeping the damaged side too dry. The needles had less water in them than on the other side so when the drying occurred in the winter that part of the plant was the most severely affected. I also noticed some plants in our nursery that were not damaged to any great extent even though they were grown in full sun.

I have noticed profound differences between cultivars as relates to their resistance to the ‘burn’ or browning caused by the winter’s desiccating conditions. The cultivars ‘Taunton’ and ‘Everlow’ showed minimal winter damage while the cultivars ‘Hicks’ and ‘Densiformis’ were fried. ‘Taunton’ and ‘Everlow’ are certainly two cultivars to remember for future use.

Cultivar differences in burn resistance were quite evident at Johnson’s Nursery. ‘Everlow’ Yew is on the left and ‘Densiformis’ Yew is on the right.

So what can be done with the yews that were damaged? Will they recover?

My advice to those that have experienced this burning on yews is to be patient. Wait for your plants to show their buds. Once you see these buds beginning to pop, you will know how far back into the plant there is live tissue. Then you can prune them back to that point and let the new growth cover up the damage. As the season moves on, the plant will shed the remaining brown foliage or it can be shaken off with little effort.

The depth of which the burn affected Yews varied from plant to plant. Check the level of burn inset and shear back to green foliage as illustrated in the right-side image.

An over-reaction to winter burn on Japanese Yew. They would have recovered!

Spruce – Picea

Not all spruce were damaged but some were. Alberta Spruce, Picea glauca conica probably took the biggest hit. Similar to the yews, the South and Southwest sides of plants were damaged the most severely and for the same reasons that the yews were hurt. However, one thing I find very interesting is that most spruce were not damaged. I saw a couple of Alberta Spruce plants in a cemetery in Milwaukee, us CSI investigators spend inordinate amounts of time in cemeteries, that had reversions that hadn’t burned at all while all the normal foliage around the reversions was toast. A reversion is just a branch sport, a mutation from a bud that reverts to a slightly different form. I find reversions fascinating! Anyway, I was thinking about why the reversion had not burned even though the plant it reverted from was fried.

Image caption. Left: Dwarf Alberta Spruce, Picea glauca ‘Conica’ were severely burned. Notice that the reversion on the burnt side was not affected. Why? Right: Alberta Spruce foliage on the left (much thinner!) Needles from the reversion growth on right (thicker!)

I asked my friend, Bill Reichenbach, another CSI investigator, what he thought the difference could be between the Alberta Spruce and its reversion. He thought the needles were different. He has noticed that the foliage on the reversions is usually thicker and may have a broader layer of cuticle on the leaf that lessens the amount of water loss compared to the mother Alberta plant. I think that the mass of the leaf itself would allow it to preserve more of its water resource as well. It is certainly interesting to think about.

We must always remember in this kind of investigation, it is a combination of all elements that causes the result—the weather, the other environmental conditions (soil, grade, sun exposure, salt exposure) and the condition of the plant itself (its genetics, its physiological condition, and its age). Few other spruce were damaged during the winter in the nursery with the exception of some ‘Mucronuta’ Norway spruce and sporadic burning on the south sides of some Norway and Serbian Spruce seedlings. This damage wasn’t major as the brown needles will drop off but the buds on the burned shoots are still viable. They should grow out of it. The Alberta Spruce on the other hand look to not only have lost foliage but the buds on the burnt branches look dead as well. I’m afraid the entire sides of plants will not regenerate new foliage thus disfiguring the plants for a long time. They could be ugly for five to ten years or more depending on the severity of the burn. Replacement may be appropriate for many of these plants. If you are unsure as to the extent of the damage just wait to see how they bud out before cutting on them.

Alberta Spruce buds close up. Healthy Alberta Spruce buds from the north side of the plant; Dead Alberta Spruce buds from the south side of the plant.

Pine – Pinus & Fir – Abies, Psuedotsuga

Relatively few Pines were damaged this past winter but some were. Lessons can be learned from these occurrences. New plantings that were put in late in the fall were particularly punished. I’ve observed numerous landscapes that were installed late that have nearly totally brown Pines in them. The common practice in our industry is to install Pines, Spruce and Firs early in the fall or late summer for best establishment. At our company we don’t recommend planting most B&B conifers after October 15th and prefer to get them in before October 1st. The absolute best time for planting these materials is between August 15th and September 15th. Normally this is the time when summer temperatures have started to moderate and the ground is good and warm. Conifers planted then will have enough time to readily root in before cold temperatures halt growth. It gives the plants the ability to maintain its water resource right up until the ground freezes. This is why watering evergreens right up until freeze up is important.

South facing White Pine, Pinus strobus, along a busy road with heavy exposure to salt spray.

I noticed burn on White Pine in isolated areas. Most susceptible seemed to be plants along roadways that were planted on the top of retaining walls or berms. It seemed to me that these plants probably lost access to water earlier than those planted at flat grades where the frost would likely have driven in considerable later than on these raised sites. In addition, locations along roadways usually get salt spray from the splashup by cars. This will likely affect the water balance in the cells of the plants as well—or as my wife Lori said to me when we were discussing this, “It will add insalt to injury”.

Concolor Fir, Abies concolor (left), and Douglas Fir (right), quickly lost their brown needles this April. Their buds looked plump and alive!

The various Firs in the nursery were browned out rather severely. Some individual plants were spared but most had some damage on them. Douglas Fir was quite erratic with some plants being totally defoliated when I observed them in late April while other individuals had some browning on the outside of the South and Southwest sides but were OK otherwise. Concolor Firs had similar symptoms, though they still had their brown needles. When I looked at the Concolor Firs up close and touched them to see if the wood looked alive, the needles dropped into my hand. I’m sure they have all shed by now. The buds looked alive on all the firs I looked at. So those of you with Firs, please be patient. I think the buds will pop new growth this spring. The plants will look goofy for a couple of years, with bald interiors and just twigs of new growth on the extremities. They should be fully recovered after three years.

Junipers – Juniperus

Canaertii Juniper, Juniperus virginiana ‘Canaertii’ burned severely at Johnson’s Nursery while Juniperus virginiana ‘Hillii’ to its right was untouched.

Of all of the browning evergreens this winter, this is the group that most surprised me. I had never seen damage as extensive as this to Junipers in my 35 years of observing woody plants. These are usually very tough durable plants and can take any winter that Mother Nature can throw at them.

This past season was different.

Junipers are one of the latest growing conifers if not the latest growing conifer in our area. My theory is that the dry September in combination with the warm moist October and November, followed by the quick, dramatic freeze up in late November and early December caught many of the Junipers before they could get fully prepared for winter. I think this is why we see many plants with the brown tips on them this spring. This foliage wasn’t completely hardened when the winter hammer came down.

There were considerable differences between cultivars in our nursery. We only field grow Upright Junipers so those are the ones I assessed most extensively. Those cultivars which were most severely burned were: Juniperus virginiana ‘Burkii’, Juniperus virginiana ‘JN Select Green’ — Emerald Feather™ Juniper, Juniperus virginiana ‘Cupressifolia’, Juniperus chinensis ‘Hook’s #8’, and Juniperus virginiana ‘Glauca’. Some others at the nursery had spotty tip die-back but not as severe as the cultivars I have mentioned. Young plants that weren’t under the snow were particularly hard hit. They are often the last to stop growing and don’t have as deep of roots as the big guys. At least that’s what I think explains the difference in burning.

I noticed extensive browning evergreens in landscapes around the Milwaukee area on: Juniperus virginiana ‘Canertii’, Juniperus sabina ‘Sea Green’ — Mint Julep Juniper, Juniperus chinensis ‘Pfitzer Compacta’, Juniperus chinensis ‘Pfitzer Glauca’, Golden forms of Juniperus chinensis and several other cultivars I couldn’t identify. I suspect a lot of this damage had to do with the locations of the plants or late pruning because I also saw specimens of these plants that had little to no burn.

The native Juniperus virginiana — Eastern Red Cedar growing along roadways throughout Southeast Wisconsin were impacted to various degrees by the winter. I observed browning evergreens that were burned completely on their outer extremities while others in close proximity were just fine with little to no burn. I suspect there is genetic variability among seedling Juniperus virginiana in their ability to withstand such a winter. Salt spray also likely played a large role in the damage on these roadside plants.

It looks like the junipers were just damaged on the outsides of the plants and can be easily fixed up by shearing off the burnt foliage.

Arborvitae – Thuja

Image caption. Left: Thuja plicata ‘U.W.’ are the green plants to the front and right. In the back of the first row is Thuja plicata ‘Excelsa’ with severe burn. Right: Thuja x ‘Green Giant’ suffered severe burn in the fields at Johnson’s Nursery

Arborvitae held up surprisingly well this winter with a few exceptions. Some plants of Thuja occidentalis, Eastern Arborvitae in extremely exposed locations burned on the Southwest sides of the plants. I saw minimal burn in our nursery on the Eastern Arborvitae. Some cultivars derived from the Western species, Thuja plicata had some major burn. ‘Excelsa’ and ‘Green Giant’ were severely burned on the South and Southwest sides of the plants. I had seen burning on small plants of these cultivars several times in recent years but never on plants 3’ and up. This year all sizes were severely damaged in the nursery. Most interesting to me was the fact that the Thuja plicata ‘Fastigiata’ and Thuja plicata ‘U.W.’ planted right next to the burned cultivars were unscathed.

I am not sure whether the damaged cultivars of Thuja plicata will recover. I will wait to see where the new growth comes from to make a determination if they are salvageable.

My investigation of this year’s tragic set of events involving browning evergreens has been intriguing. I have come up with the usual set of guilty parties in association for this caper, namely, the sun, the cold, the wind, insufficiently hardy plants, and unfortunate sittings of plants, salt spray, and inferior genetics. It was definitely a conspiracy! What I have found to be the most interesting thing of all through this investigation is that the plants themselves are the greatest teachers of horticulture out there. Their relationship to each other and their environment provide all the important clues for me and you to understand their strengths and weaknesses and which are best suited to our challenging world.