Bert Cregg

Checking up on FreezePruf

As winter continues to hold its icy grip over the middle of the country, our thoughts don’t stray too far from plants and cold. Recently one of the graduate students in our department, Nick Pershey, brought to my attention a new product called FreezePruf that claims to improve plant cold hardiness by up to 9 degrees F. Since a couple of degrees of improved cold tolerance can be a big deal (just ask a Florida citrus grower after a 29 deg. F night), nine degrees F. is huge. At first blush, FreezePruf looks ripe for the Garden Professors’ picking. The promotional claims are sensational and are followed by the obligatory exclamation points. “Just spray it on. It’s like moving your temperature zone 200 miles south!” So the obvious questions are: What is it? What does it do? Does it work?

What is it? FreezePruf is a mixture of several fairly common compounds. These include WiltPruf (a film-forming anti-transpirant), SilWet (a surfactant – helps material spread and stick to leaves), AgSil (potassium silicate), polyethylene glycol (an osmoticum – PEG is widely used in cosmetics and laxatives), and glycerol.

What does it do? To understand what FreezePruf does it’s helpful to understand how freezing injury occurs in plants and how plants tolerate freezing. First, remember that water exists in plant tissues between plant cells (extracellular) and within cells (intracellular). When plants are exposed to freezing temperatures ice forms first between cells (extracellular ice) but not within the cells. This is due to the fact that water within cells contains solutes that depress the freezing point. Freeze damage can occur in a couple ways. One is ice formation within cells (intracellular ice). Tissues can also be damaged if cells become excessively dehydrated as a result of extracellular ice formation – the ice between cells acts like a salt or osmoticum to continue to draw water of the cell and into the intercellular spaces. The formulation of FreezePruf apparently acts to depress the freezing point within the cells (due to potassium ions and PEG) and to limit cell dehydration.

Does it work? At present the only data available on FreezePruf is from the product developers in their patent application. To date, nothing on the product has been published based on peer-reviewed studies; which always makes the Garden Professors skeptical. The product development team, however, is lead by Dr. David Francko, a plant biologist and Dean of the Graduate School at the University of Alabama. Data in the patent application show improved cold hardiness on the order of about 4-5 deg. F for a variety of cold sensitive plants, mostly palms, bananas and annuals. In some cases the protection was only a couple of degrees but in one case ranged up to 9 deg. F.

What’s the bottom line? For most gardeners the principle benefit of FreezePruf would be to protect plants from the first few early frosts in the fall. The question is whether you’d rather spray a relatively untested product versus relying on tried and true methods (e.g., bringing container planters in, covering sensitive plants with old bedsheets). The developers claim FreezePruf can last up to 6 weeks – that could save a lot of dragging bedsheets around the yard.

Caveats: FreezePruf is marketed as ‘Eco-Safe’ – whatever that means – although the MSDS sheets of some of the component products indicate eye and skin irritation are possible. Until a longer-term database is available I would be cautious of unintended results. For example, could this stuff make plants more attractive to pets or wildlife? We’ve seen reduced cold hardiness in conifers using WiltPruf alone, it would be interesting to see some data on Freeze-Pruf on conifers before recommending it for use on those.

The evolution of tree care

I’m one of those people who can’t resist things that are free. When you pass a yard that has a ‘FREE’ sign on a rusted-out lawn mower or an old piece of exercise equipment and wonder, “Who on earth would take that home?” Uh… that would be me. Actually, I blame my dad. The Old Man’s garage was crammed full with outboard motors missing pull-cords, mismatched lawn furniture, and all manner of secondhand tools in varying states of disrepair. So my defect is genetic. Only my hyper-organized wife prevents my garage from suffering the same fate as my dad’s. But, like a blind pig finds an acorn, sometimes a scavenger finds something interesting. Recently a retiring professor in our building was cleaning out his office and put a stack of old books on a table by his door. And there was the magic word: FREE. I sifted through the stack and found my treasure; a 1948 edition of Maintenance of Shade and Ornamental Trees by Dr. P.P. Pirone. Granted, I have ready access to several modern tree care texts plus an ocean of information on the International Society of Arboriculture (ISA) website, but after thumbing through a few pages I knew this one was a keeper. The main reason the Pirone book interested me was to see how tree care has changed over the years and how things have stayed the same.

What’s changed? The most obvious example of how tree care has changed in 60-plus years is that an entire chapter of the 1948 text is devoted to cavity filling. For those not familiar with the process; cavity filling, as the name implies, is the practice of filling hollow areas in trees with concrete, just as a dentist fills a tooth cavity with amalgam or composite materials. Filling cavities in trees was once a relatively common practice. Today we recognize that filling does not stop decay and there is little value in the practice (and it certainly complicates removals). If anything, we would replace this chapter with ‘hazard tree assessment’, seeking to determine if the tree has enough solid wood to be structurally sound.

Filling a tree cavity.

The finished job

What hasn’t changed? I was surprised to see a fairly lengthy discussion of problems related to girdling roots from 60 years ago. This actually causes me to eat a little crow. I have sometimes questioned whether the current ‘epidemic’ of girdling roots is actually related to the fact that arborists and urban foresters are spending more time looking for them and have better tools (specifically air spades) for finding them. Of course, Pirone’s text also suggests that girdling roots were an issue before the advent of evil nursery production systems such as container growing. The discussion of treating girdling roots points out another change in practices. In 1948 the arborist was advised to carefully dress the wound with paint or tar. Today we generally advise against treating wounds except for situations which risk certain exposures such as if oak trees must be pruned when they are at risk for infection from oak wilt.

Girdling root removed and wound dressed.

So there you go, another book to clutter my shelf and another example of one man’s trash turning into another man’s treasure. I think Dad would have been proud.

Blue Spruce Blues

One of the roles I’ve evolved into over the past decade as an extension specialist at MSU is that of ‘the Conifer Guy’. Conifers are great and fascinating plants. The oldest trees in the world are conifers, the largest trees in the world are conifers, and some of the most interesting (at least to me) landscape plants are conifers. Unfortunately, for a variety of reasons, in the Upper Midwest we have gravitated to Colorado blue spruce more than just about any other conifer. Part of this over-reliance on blue spruce in the landscape is driven by production (see, Linda, I’m not always an apologist for nurseries). Growers want to grow what they know and what’s easy to grow. As a nursery tree, blue spruce is a reliable performer that is well adapted to a relatively wide range of site conditions. Of course, growers also want to grow what they can sell, and there always seems to be a steady demand for blue spruce. In many neighborhoods it appears that there is an ordinance that every other tree has to be a blue spruce. So what’s the issue? In the Great Lakes region, blue spruce often look pretty good when young. However, as trees age they become susceptible to several major pests, especially cytospora canker and gall adelgid. So all those shapely blue Christmas trees that were planted 10 or 15 years ago are now a bunch of ratty-looking messes. So what’s the solution for blue spruce burn-out? Clearly landscapers and homeowners need to think beyond blue spruce and look for a greater variety of choices. Here are three to consider.

– Serbian spruce Picea omorika Whenever I’m asked to suggest a conifer, Serbian spruce is usually one of the first trees in the conversation. While the color may not be as striking as a blue spruce, Serbian spruce still has impressive needles in its own right – bi-color with dark green on the upper side and silver below. Adding to Serbian’s charm is its graceful weeping habit.

– Swiss stone pine Pinus cembra The late, great conifer expert Chub Harper used to remark, “I never met a cembra I didn’t like.” Chub’s fondness for Swiss stone pine was well founded. Here is an understated, consistent landscape performer. Few pests, dark green needles and stately upright form.

– Korean fir Abies koreana It would be a stretch to consider Korean fir an alternative to blue spruce. While Korean fir is more broadly adapted than many of its pantywaist cousins in the genus Abies, it will still do best on the Holy Grail of moist, well-drained slightly acidic soils. Nevertheless, Korean is tougher than the average fir and is a conifer with some character and worth a shot. Korean firs are often heavy cone producers, which can add an interesting element of color.

And now for something completely different…

From this week’s e-mail file…

“Dear Dr. Cregg:

As I’ve done for many year, this year I harvested my “wild” Christmas tree from the Huron-Manistee National Forest. I cut the tree at ground level. Soon after I brought it home, it started sprouting new light green clumps of needles at the tips of many branches. Is the tree actually growing? It doesn’t seem possible that it’s still alive, but it seems to be thriving and I hate to toss the tree to the curb if it’s fighting for life. I am tempted to leave it in the tree stand to see what happens….”

Pat M.

Midland, MI

Dear Pat:
The tree is dead, it just doesn’t know it yet. Depending of the species, some Christmas trees will break bud and begin to grow once they are brought indoors. The tree is still alive in the sense that its needles are still carrying out photosynthesis and water is still moving up the trunk to the needles. But since the tree has no roots and no way to produce any new roots, it has no prospect for long-term survival. The phenomenon you’re observing is common in some spruces and other conifers adapted to cold regions. Before you cut the tree, the buds were exposed to enough cold to meet their chilling requirement to overcome dormancy – the only thing that keeps trees in wild from growing at this point are cold temperatures. Once you brought it indoors, the tree ‘thought’ is was spring and started to grow. If you or a family member want to do a little science project you could keep the cut end in water and see how long the tree lasts. Eventually, however, the conducting elements at the cut end will begin to plug with resins and the tree won’t be able to move enough water to meet its needs and will expire.

Regards,
Bert Cregg

Do landscape trees need nitrogen fertilization?

I’m in Grand Rapids this week attending the Michigan Nursery and Landscape Association/Michigan Turf Foundation Great Lakes Trade EXPO. The topic for my talk today was Landscape Tree Fertilization. That might not sound like a subject that would generate controversy, but as with most things, there are camps emerging. There is a rising chorus of folks that suggest that landscape trees should not be fertilized with nitrogen. There are a couple of lines of evidence that bolster this point of view. First, many systematic studies on the growth response of street trees or landscape trees often do not show a response. There are numerous examples of this, for example, in Arboriculture and Urban Forestry (formerly J. of Arboriculture). The second line of evidence for not fertilizing landscape trees relates to the relationship between tree nutrition and susceptibility to insect pests. This argument relies on the ‘growth vs. defense’ hypothesis and suggests that fertilization promotes growth at the expense of defense compounds; essentially making fertilized trees tastier to insect pests.

So, in light of this, why do I suggest that landscape trees should receive 1-2 lbs of N per 1000 sq ft. every 2-3 years? First, we need to understand that nitrogen is constantly lost from landscape systems. In forests, trees take up nutrients from the soil, translocate them to leaves, shed the leaves, and the nutrients are ultimately returned to the soil in a cyclic process. In landscapes, leaves are usually raked or blown and removed from the cycle. Soil nitrogen is also lost due to nitrate leaching. Additionally there are often key weaknesses in some of the papers that purport to show no response to fertilization. For example, Ferinni and Baietto (Arb & UF 32:93-99) found no response of sweetgum trees to two levels of fertilization. However, the data show that the control trees, which were not fertilized, had similar (and fairly high) foliar N levels as the fertilized trees. This pattern can be found in several similar studies. The more appropriate conclusion for these papers should be “Trees that are not nutrient deficient do not respond to fertilization”. Similar issues pervade studies related to the growth vs. defense hypothesis. Why would one presume that a nutrient deficient plant would be better able defend itself against insects attack than a tree that has adequate nutrition? Ideally, fertilization decisions should be based on visual symptoms and soil and foliar samples. Nevertheless, low rates of N from either organic or inorganic sources will make up for losses from the N cycle and maintain tree vigor.

It should be noted that the rates I’m suggesting are considerable lower than those that are found in some older extension literature, which recommend rates of N up to 6 lbs for 1000 sq ft. As a point of comparison, Midwestern farmers apply 150-200 lbs/acre to grow a crop a corn. The 6 lb rate for landscape trees works out to around 260 lbs per acre!

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O Tannenbaum!

Twas the blog before Christmas… My last chance to post about Christmas trees for another year. I’m always surprised when I troll around the web or do interviews how many myths about Christmas trees still abound. So in the spirit of the season, a little Christmas tree myth-busting.

“Good grief. I’ve killed it.”

Using a real tree hurts the environment
Here’s a real post from the e-how.com website:

“Its so not fair to cut down all those baby trees, use them for a few weeks and then toss them by the curb for garbage removal. Everytime, i pass by a house and i see those poor trees just shoved out like that it breaks my heart. they belong in the forest or backyard where they were meant to be, growing old and improving the air and atmosphere. i used to like real Christmas trees but not anymore.”

Yes, Virginia, there are still people out there that think Christmas trees are cut from forests. The U.S Forest Service and some state forestry departments do offer permits to cut Christmas trees but this is a tiny fraction of the trees used in the U.S. Virtually all Christmas trees sold at tree lots and stores are grown on Christmas tree farms for that purpose. For each tree cut, growers plant two or three more. Moreover, many communities have programs for re-cycling Christmas trees into mulch or compost.

Christmas trees are a fire hazard.
The key here is water. Fresh Christmas trees that are properly watered are not a fire hazard. Trees that are allowed to dry can be a fire hazard. These are the ones your local TV station uses for their annual dramatic Christmas tree fire video.

Fire retardant sprays make Christmas trees safer.
Research by Dr. Gary Chastagner, a colleague of Linda’s at WSU-Puyallup, has shown that some fire retardants can actually increase tree moisture loss. Maintaining tree moisture is the key to making trees safer and improving needle retention. Making sure the tree stand never dries out is much more important than a fire retardant spray.

Injecting water directly into the stem is the best way to maintain tree moisture content.
This is a case where a little knowledge can be a dangerous thing. Since water moves up the tree through the xylem elements in the stem, wouldn’t injecting water right into the stem be the best way to water? That’s the logic behind the Tree I.V. As the name implies, this device is like an I.V. drip for your tree. Drill some holes in the trunk, attach some tubes to a jug a water, and voilà, a self-watering tree! We can thank Gary Chastagner again for busting this myth. He and some colleagues found that displaying a tree in a regular tree-stand with water maintained higher tree moisture levels that the I.V. technique.

So, if arborists can use trunk injection to apply pesticides and fertilizers to trees, why wouldn’t the Tree I.V. work? Actually, the tree I.V. does work in the sense that the tree will take up water from the jug. The problem is that the tree may not take up enough to meet its total water need. In a normal stand, the entire stem cross section is exposed to water. With the tree I.V. only a portion of the stem will be translocating water. Plus, conifers contain resin ducts which clog injection ports. This is one of the reasons why arborist’s trunk injections don’t work as well as on conifers as they do on most hardwoods.

Bottom-line, keeping your Christmas tree hydrated is the key to retaining needles and keeping the tree safe. A good rule of thumb is that a stand should hold a quart of water for each inch of tree caliper at the base. For most trees this means a stand that will hold at least a gallon of water. Check water in the stand daily and never let the tree go dry.

Have a very merry Christmas!

Are natives the answer?

Last week Jeff kicked off a lively discussion about invasive plants. Let me state up front that no one on this blog is promoting invasive plants. But the issues surrounding invasive plants are extremely complex and have profound implications for many groups with whom we work in landscape horticulture and urban and community forestry. It is essential in these discussions that we separate fact from hyperbole. In some quarters, lines have been blurred and people fail to make key distinctions and lump exotic, alien, or non-native species together with invasives. According to the Federal Executive Order on Invasive species “Invasive species” means an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health. All invasives are alien but only a small fraction of alien species are invasive (all humans are mammals but not all mammals are humans). Nevertheless, there is a temptation to ‘hedge all bets’ and promote only native species for horticultural planting since native plants, by definition, cannot be invasive. In addition, there is a ‘feel good’ aura that surrounds native plants – if they’re native they must be good – that clouds some of the logic in the argument.

Some examples:

Natives are more stress tolerant and better adapted than exotics.
Really. If native plants are always better adapted, why do we have invasives? Shouldn’t the “better adapted” natives out-compete them? Stress tolerance and adaption are a function of natural selection pressures of the environment in which a species or population evolves. The world is full of stressful environments and, therefore, lots of stress tolerant species. There is no a priori reason, for example, to believe that a native species needs less water than an exotic. The ability to withstand drought depends on the particular species in question. I’ve done a lot of research on stress physiology of Scots pine – few, if any, native species here in Michigan can match it for drought and cold hardiness. Moreover, as Jeff pointed out, most of our urban and suburban environments no longer reflect native conditions. Urban heat islands can result in temperatures 10-20 deg. F warmer than the native countryside. In our research on heat island effects in downtown Lincoln, NE we logged temperatures in tree canopies in excess of 125 deg. F. These temperatures were coupled that with the usual urban conditions of impervious surfaces and compacted soils – what tree species is native to that ecosystem?

Native restoration? This nurse-log ecosystem is typical of forests in western Oregon & Washington. Trying to keep it alive in downtown Portland requires constant mist irrigation..

Native plants are more pest resistant than exotics. This would be true if native pests were all we had to contend with. But the exotic pest train has already left the station. Emerald ash borer, Dutch elm disease, white pine blister rust, chestnut blight, Asian long horned beetle, and sirex wood wasp are here and here to stay. And their friends are coming. The continued expansion of global trade will almost undoubtedly mean that exotic pests, for which native trees have not evolved resistance, will become more, not less, of a problem in the future. Relying exclusively on native trees means more, not fewer, catastrophic tree failures. Heavy planting of green and white ash, which are both native in Michigan, has resulted in the loss of 30% or more of the urban tree canopy to EAB in some Michigan communities.

Natives increase diversity This presupposes that exotic species do not or cannot fill niches occupied by natives. Exotics can certainly add structural diversity and age class diversity to an urban and community forest. I would also argue that they add to species biodiversity as well. If we consider an urban community such as Lansing or Detroit, there are maybe six or seven native tree species that we could expect to have reasonable longevity as street trees. If we expand our choices to include non-natives we can expand the list to twenty or so. Not a huge number to be sure, but still a better hedge against catastrophic urban tree loss that the ‘native only’ policy.

Where to go from here? We cannot ignore that fact the invasive plants are a huge economic and environmental issue. Presently we do not have models that will accurately predict which exotics will become invasive and which ones won’t. Trees that are demonstrated to be invasive in a given environment need to be dropped from planting programs. Except for the desert Southwest and parts of the Plains, every region of the country has great native trees that can. and should, be an integral part of their urban and community forests. While it’s tempting to play it safe and promote natives only, this policy has significant shortcomings. Urban and community forests provide enormous economic, environmental, and societal benefits. In order for our urban forests to provide these functions over the long term we need as broad an array of trees species as possible, including appropriate exotics.

Friday quiz

Thought we’d take a break from the invasive discussion (I have some throughts I’ll weigh in with on Mon.) In the meantime, here’s a photo of dwarf Alberta spruce not too far from my boyhood home in Olympia, WA. I get 2 or 3 of these calls each year; usually with a homehowner exclaiming, “I’ve got a tree growing out of my tree!”.

Growing a greener Christmas tree

Among the many hats I wear, one of the most enjoyable is that of an Extension Specialist working with Christmas tree growers here in Michigan and surrounding states. I suppose part of the satisfaction stems from the fact that my first real job was shearing Christmas trees in southwest Washington during my high school summers. To give you an idea how long ago this was, the minimum wage when I started the summer between my sophomore and junior years was $2.20 per hour.

Today I’m involved in a variety of projects related to improving sustainability of Christmas tree production, particular water and nutrient management. One of our major focus areas has been the development of container production systems for living Christmas trees. For those not familiar with the concept, living Christmas trees are conifers that are sold with their roots intact as opposed to a cut Christmas tree. Living Christmas trees serve a niche market for people that think cutting a Christmas tree is wasteful or even harmful to the environment (never mind that virtually every Christmas tree cut in the US was grown on a plantation for that express purpose). Many Christmas tree growers have sold living trees by digging trees from their fields and selling them balled and burlapped or placing them in containers. In our current work we’ve focused on growing several species of conifers as container stock with the end goal as living Christmas trees. Container growing imparts a couple of advantage over the B&B method. First, container-growing eliminates loss of roots associated with field digging. Second container-grown trees are much lighter weight for consumers to handle than field-dug trees. Also, we have found the container-grown trees survive post-holiday storage and transplanting better than field-dug trees.

My former grad student, Wendy Klooster, shows off one on the Fraser firs she grew as part of her MS project on nutrient management.

If you’re considering a living Christmas tree here are some things to keep in mind.

If your ultimate goal is to plant the tree in your landscape, make sure the tree is a species that’s hardy in your location. There are several types of container-grown conifers such as Italian stone pine (Pinus pinea) sold in big box stores and super markets that are hardy in only the warmest parts of the country.
Limit display of living trees to 10 days to two weeks. Most conifers will begin to lose dormancy shortly after being brought indoors. We’ve observed that some, such as Black hills spruce (Picea glauca var. densata), will break bud if the weather has been cold and they’ve had sufficient chilling.
After the holidays, place the living tree in a protected but unheated space such as a garage or enclosed porch or patio. The key here is that the tree needs some exposure to light – but avoid direct sun.

As with just about everything these days, the environmental friendliness of Christmas tree production is receiving increasing scrutiny. One way to have the ‘greenest’ tree on the block is to bring home a tree that keeps on giving.

Salt solutions

Hopefully everyone got their filling of turkey and dressing over the long Thanksgiving weekend. I used our unusually mild weather on Saturday to celebrate a time-honored tradition around the Cregg farm: The annual cursing of the tangled Christmas lights.

Turning the calendar over to December in Michigan means another Midwest tradition is just around the corner as well: The annual dumping of the road salt. Although totals vary, at least one source estimates that road crews pour 8 million tons of salt on roads in the US each year. The effects of this sodium chloride are readily apparent on our vehicles – in Michigan it’s rare to see a vehicle more than 10 years old on the road – and drivers of those older cars that remain can usually see the road pass under them through a rusted-out floorboard. Of course all this road salt has profound implications for landscape plants as well. Sodium chloride can damage plants in several ways. Both sodium and chloride can cause direct toxicity, particularly from salt-laden spray drift from highways. Salt in soils can cause osmotic stress resulting in drought injury. Sodium in soils can displace potassium, magnesium, and other essential plant elements. High levels of chloride in plant tissue can reduce cold hardiness and make plants more susceptible to freezing injury. Suffice to say that salt is bad for plants.

So what’s a plant lover to do? In general I advise a two-phase strategy of Selection and Protection for homeowners and landscapers that have to deal with heavily salted roads. By Selection I am referring to planting salt tolerant plants (or at least avoiding salt sensitive ones). The poster child for a poor choice in Michigan is eastern white pine, which is extremely intolerant of road salt. Witness this planting at a rest area along I-96 between Lansing and Detroit.

Don’t you love to see your tax dollars at work? Even a cursory look at a list of salt sensitive plants would have been a tip-off that that white pines and highways are a bad mix. Most blog readers should be able to come up with a list of salt tolerant or salt sensitive plants for their area by Googling their way around the internet. A couple caveats about these lists: First, many are based on anecdotal experience, not hard data, so you may see inconsistencies between lists. If possible, try to consult several sources and look for a consensus opinion about the plants you’re interested in. Second, many recommendations are dated and include plants that may be considered invasive or no longer recommended for planting. One list I just looked at included Russian olive (invasive) and green ash (no longer planted in the Midwest due to Emerald ash borer).

Another approach to reducing salt damage to plants is Protection. Here I am referring to erecting a physical barrier to block salt spray or salt splash from reaching plants. The most typical form of barrier around here is a wooden frame or fence covered with burlap or canvas. Some people will actually wrap their evergreen trees or shrubs with burlap. This may help against winter desiccation but does little for salt since the salt-saturated burlap will still be in contact with the foliage. Obviously aesthetics go out the window with the protection approach but I’m noticing more and more people are willing to put up with a couple of months of looking at burlap to keep their plants looking thrifty the rest of the year. In northern Europe some road systems will line their roads with pre-formed plastic barriers to reduce salt splash to adjacent vegetation.

What about alternative deicers? This is a question I get frequently when I speak about salt and plants. There are several things to consider about alternative (i.e., not sodium chloride) deicers. First is the cost. All alternative deicers are more expensive than salt, some by a factor of 10 times or more. This often limits their widespread use for highway departments. Many road crews will use alternative products around bridges and other sensitive areas where they want to limit corrosive damage. Alternative products may also be useful for smaller scale operations such as parking lots and walkways. Secondly, many alternative deicers contain calcium and/or magnesium chloride. These may even be marketed as ‘plant safe’ since they contain calcium and magnesium, which are essential plant elements. The problem is the chloride. Chloride is a plant nutrient but is only needed in minute amounts (a few parts per million). At higher levels it becomes toxic.

A study in Colorado found tree damage due to chloride near roads which were treated with calcium and magnesium chloride for dust abatement. For safer alternative deicers consider chloride-free products such as calcium magnesium acetate.

In the meantime here’s hoping for a mild winter for everyone.