Plant care – Page 4 – Sticks & Stones

Non-Fall Hazard shade trees

It’s almost that time of year for digging trees. There are some risks when it comes to fall digging season and you might be wondering what those risks are and what is safe to dig.

When handled correctly, many trees can be safely moved in the fall; however we have a list of trees that are considered poor candidates.

Christensen's Plant Center Fall Digging Hazard Trees

For instance, if a freshly-dug tree is slow at regenerating roots or lacks new established roots, that tree could be considered high risk. Thin-barked twiggy trees like birch and willow are also at high risk due to having trouble retaining moisture during the winter months. Fall planted trees of any species still require water going into the winter and many losses can be blamed on the tree drying out.

Even though Red maple is on the Fall Hazard list, the Freeman Maple hybrids (Acer x freemanii ) like Autumn Blaze® (‘Jeffersred’) are not considered a poor risk. Being a cross between silver and red maple, they are tough, fast growing, adaptable trees. They are drought tolerant when established and hardy to Zone 3, making them good candidates for fall digging. Norway (Acer platanoides) and Sugar (Acer saccharum) maple also tend to move well in the fall.

Some others to consider are Ginkgo and ‘Ivory Silk’ Tree Lilac (Syringa reticulata) - even though that last is not technically a shade tree we do see demand for them in landscapes where space is at a premium.

Any of our knowledgeable staff would be happy to help answer questions or give you the most suitable substitutions regarding fall hazard trees.

Visit these links for more information about Fall Hazard trees:

Fall Hazard tree lists explained (Sticks & Stones, Jeff Good)

Transplanting and a Deeper Look at “Fall Hazards” (NYC Parks Director of Street Tree Planting Matthew Stephens and Taking Root Editor Michelle Sutton)

Boxwood Blight

You may have heard of a new fungus that has been damaging and killing boxwood in the US. It was first identified in Connecticut in 2011. Called Boxwood Blight, it has now been seen as near as Ohio. It has been predicted that it will continue to spread. Spores can be transferred by physical contact, splashing water, or wind.

Christensen’s Plant Center is taking the necessary steps to make sure that we have clean boxwood in stock for you at all times. This means following the best practices that have come from growers and distributors across the country.

Boxwood Blight is easily transferred by physical contact. Even brushing up against an infected plant means that you can transfer the fungus onto other plants later that day. To that end we must ask that you observe the following when visiting Christensen’s Plant Center.

Please do not bring Boxwood plants or parts of a Boxwood into CPC. We will continue to do our best to identify any plant material via a photograph, but we can not have possibly infectious plants brought into our clean nursery.
We will no longer accept any returns of Boxwood for any reason. Again, we cannot accept materials back once they have left our clean environment.

These practices are for your success as well as our own. Maintaining a clean facility ensures that we will be able to provide you with material that is free of Boxwood Blight for all of your projects now and in the future. Thank you for your help!

Click image for larger size

In the links below are PDFs with more information about this disease.

MSU Extension - Boxwood Blight Disease in North America (2.33 MB)

CAES - Boxwood Blight - A new disease for Connecticut and the U.S. (1.05 MB)

Mid-season fertilizing

Should I be fertilizing my trees and shrubs in August?

Ask five experts that question and be prepared for five different answers, at least that happened to me. Regardless of the type or size of your new landscape, maintenance will be required to ensure it stays healthy and looking the way it was designed to look. Although 95% of all problems with new plant material can be attributed to improper watering, fertilizers are going to play a big part in getting things established and staying healthy.

Early spring and late fall are obviously your major fertilizing moments, but let's look at right now. New plantings will be aided by the use of some starter fertilizer, especially at new housing and businesses where a lot of good soil has been stripped away. Some cities have poor soil to begin with, lacking nutrients to give plants a good start. We carry some great organic starter fertilizer containing bacteria and mycorrhizae to increase root mass and help avoid transplant loss due to difficult conditions. Light application of these starters and plenty of water will be key during this month.

Fertilizing established plants in August is a little tricky. To avoid stressing the plant, avoid fertilizing during drought or heatwave conditions. Know your soil and fertilize only when plants are truly nutrient deficient. Why? Because new growth forced by fertilizing during this period may not harden off before the onset of winter resulting in tip dieback that won't show until next spring sometime. That's a phone call you won't want to get!

Come by our store and we will help you choose the best product for your particular situation.

Why is my blue spruce turning green?

Colorado blue spruce is one of the most popular evergreens we sell. The straight species is usually green, but the cultivar 'Glauca' ranges from bluish-green to an eye-popping silvery blue. The color is genetically determined and before grafting ornamental trees became the norm, the brightest blue seedlings were known as "shiners" and were selected out and sold at a premium. Now we have numerous cultivars with consistent, bright blue color.

So why might you get calls from customers complaining that their expensive blue tree is turning green? Firstly, the blue color is only present on the new growth, weathering off in time. Pesticides can strip off this waxy blue coating from the needles as well. Other culprits can be air pollution, or poor growing conditions that keep new foliage to a minimum.

Once the blue color has worn off the needle, nothing will bring it back and the tree is going to look green until that flush of new growth each spring. However, you can encourage the best possible color by providing ideal growing conditions and care. Spruce prefer moist, well-drained soil, and you may fertilize established trees in early fall or mid-spring.

How to shear boxwood and yew

People are always asking me about the best time to prune the shrubs they've installed or are maintaining. For flowering shrubs the answer is easy - prune right after they’re done blooming. Late pruning in this case is bad since you’re removing the next season's flower buds and most of your clients would not be happy about that.

Boxwood (Buxus) and yew (Taxus) are a little different as flowers are not necessary or desired. First and foremost, always use very sharp pruners or shears, to make the pruning easier and reduce damage to the plant. To maintain trimmed forms and hedges you ideally need to shear twice a year. Once in late May or early June after the initial foliar flush, and then a second time around August. This causes the formation of lateral buds which help maintain denser growth.

Keep in mind that shearing a plant to the same exact size every year causes the outside of the plant to become very dense, leaving the interior bare. Allowing for a slight increase helps delay the need for an extreme renewal pruning or plant replacement. Try not to prune during a drought period, and to prevent foliar freezeback pruning should never occur in late fall or winter. If you’re only going to shear once a year, try to do it around August.

When shearing hedges, taper them so that the top is narrower than the bottom, so all sides will be exposed to sunlight. This will give you a slightly pyramidal shape. Avoid at all cost the inverted pyramid look, as this even further screens sunlight and eventually kills the bottom.

Both boxwood and yew are very tolerant of shearing and with proper technique will remain attractive and functional in the landscape for many years.

Are native plants always better?

Native plants have their place in landscaping. It is in native areas. Attempting to force native plants into landscapes in urban areas is difficult for everyone and everything. The plants will have a difficult time being successful in those conditions, and often the property owner and the landscape contractor are not prepared for the amount of maintenance it will take to make this successful. And neither are prepared for the financial commitment to make this successful.

For the last several years there has seemed to be a push to have more natives included in landscapes. To say that I am not a fan of this is not a secret. But it is always nice when someone with Ph.D after their name supports your position. Please read the below article by Dr. Linda Chalker-Scott about how native plants might not be good choice for most landscapes in urban areas.

Black Chokeberry (Aronia melanocarpa) a Michigan native

The Myth of Native Plant Superiority:

"Always choose native plants for environmentally sustainable landscaping."

by Linda Chalker-Scott, Ph.D.

Extension Horticulturist and Associate Professor
Puyallup Research and Extension Center
Washington State University

The Myth

In recent years, people have become more interested in native plants and landscapes as natural ecosystems continue to shrink. This admirable dedication to our natural world heritage has manifested itself in native gardens springing up in every place imaginable. At the same time, I see more of these native gardens suffering from disease, pests, and general decline. What’s happening? Aren’t native plants supposed to be resistant to local pathogens and parasites?

The Reality

There are some urban areas where many native plants just do not survive (or do so only with substantial maintenance). Such areas can include parking strips, traffic circles, and parking lots: in short, areas with limited soil area and a lot of environmental stress. Consider the realities of these landscapes:

Discontinuous, dissimilar layers of topsoils and subsoils with poor drainage and aeration
Significant compaction and other physical disturbances as a result of animal, pedestrian, and vehicular traffic
Alkaline pH due to leaching of lime from concrete
Inadequate or improper fertilizer application
Lack of mulch or other soil protection
Lack of adequate water in summer months
Increased heat load from asphalt reflectance
Air pollution

Many of the trees and shrubs native to our region evolved in thin, acidic soils with adequate moisture to maintain soil and plant water status. When these species are installed in urban landscapes with significantly different soil and water characteristics they are challenged by a new set of environmental circumstances. As landscape plantings begin to suffer from multiple stresses, they become prone to invasion from opportunistic insects, bacteria, and fungi. Stress can weaken a plant’s natural resistance to local pests; witness the recent decline in our native Arbutus menziesii (Madrone) populations.

Another example of the failure of native trees to survive in urban sites comes from Palm Desert, CA. Many of the parking lots there were planted in native mesquite. Mesquite survives in its arid environment by developing both a deep taproot and an extensive shallow root system. When planted into the very limited soil spaces typical of parking lot tree wells, these trees often tilt or topple as a result of insufficient lateral root development. The City of Palm Desert has recently looked to non-native tree species, including ash, to replace mesquite in these settings.

The Bottom Line

Native, temperate forest plants are excellent choices for unrestricted sites with acidic, well-drained soils.
For sites with limited, alkaline, and/or poorly drained soils, choose species adapted to environments with similar soils. Consider especially those species that tolerate clay soils.
For sites exposed to increased heat load, choose species adapted to hot, dry climates that can also tolerate cool, wet winters.
Instead of installing large trees into limited sites, consider smaller trees or shrubs that can be arborized.
Be sure to protect soils with mulch, especially where foot traffic causes compaction.
Site considerations should always dictate plant selection.

For more information, please visit Dr. Chalker-Scott’s web page at The Informed Gardener.

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA Certified Arborist. She is Washington State University’s Extension Urban Horticulturist and an Associate Professor in the Department of Horticulture, and holds two affiliate Associate Professor positions at University of Washington.

She is the author of three books: the award-winning, horticultural myth-busting The Informed Gardener and The Informed Gardener Blooms Again, and Sustainable Landscapes and Gardens: Good Science – Practical Application, a comprehensive approach to the science behind urban horticulture and arboriculture.

Two other books are in progress: How Plants Work – A Gardener’s Guide to Plant Physiology (Timber Press) and an update of Art Kruckeberg’s seminal work Gardening with Native Plants (University of Washington Press). She has published extensively in the scientific literature magazines as well as in popular magazines such as American Nurseryman, Organic Gardening, and Fine Gardening. She and three other academic colleagues host “The Garden Professors” blog and Facebook page, through which they educate and entertain an international audience.

This article was reprinted in The Michigan Landscape magazine, a publication of the Michigan Nursery & Landscape Association (MNLA.org).

Reprinted by permission to Sticks & Stones, June 2018

Don’t be “that” guy!

On my commute to work I pass a recently landscaped site that has a lot of plants still sporting their plastic tags.

I say "recent" but I really mean SEVERAL MONTHS. Seeing those tags flapping in the wind really detracted from a very nice landscape job!

Nursery growers and re-wholesalers put tags on plants for identification, not for decoration. I can see leaving the tag on for a few days on a residential job so the homeowner knows what was planted. But you probably gave them a landscape plan with everything identified on it, making those bright plastic tags unnecessary. On some commercial jobs I’ve seen tags left on for years, until they weathered off. It's not a good look.

Not only does the tag look bad, it is unhealthy for the plant. Plastic tags can girdle branches on trees, and large portions of smaller shrubs. I have personally removed tags that have become embedded in the bark as the plant grew. It does take a few extra minutes, but having your crew take those tags off will make your install look as professional as it should. Have them do this as the parting site-cleanup as they remove scraps of burlap, lengths of tagging ribbon, and snarls of tying twine. You want your client - and all his friends and neighbors - to admire your work without distraction.

Bad Karma

It has always seemed that many things were just meant to be. Peanut butter and jelly, perhaps the greatest love affair of all time. Romeo and Juliet, Desdemona and Othello, Mr. Darcy and Elizabeth, Ozzie and Harriet, Mork and Mindy, Gertrude and Heathcliffe, Joe and Kirsten, Bonnie and Clyde – the list is endless! But humanity is cursed with its fatal flaws. Peanut butter and jelly – they don’t really mix and the jelly oozes out the side of the bread. Romeo and Juliet are tragic star-crossed lovers. Othello has a serious problem with jealousy. Mr. Darcy and Elizabeth get past their pride issues, but eventually the book has to end. Ozzie and Harriet, as well as Mork and Mindy, get cancelled. Joe and Kirsten’s Days of Wine and Roses turns to Brandy Alexanders – not a good finish. And, a life of crime does not pay off for Bonnie and Clyde.

Plants, or combinations of some plants, can have similar tragic results. Some planting designs look great but eventually nature unleashes it’s fatal flaw. The design of some landscapes brings out the worst in some plant varieties. A number of these ill-fated arborial marriages exist but the coexistence of pears and junipers requires our attention.

The ubiquitous Callery Pears, strong and adaptive growers, are increasingly being bothered with Pear or Trellis Rust. To blame are junipers. And vice versa. Together they create a perfect storm scenario for the fungus, Gymnosporiangium fuscum. This is a dark, bare capsule on junipers which explodes with orange, jelly-like fingers during cold, wet springs. These galls cause dieback in junipers and rust colored spots and scabs on the leaves of pears as well as lesions on their branches. Proximate use of these plants is a marriage gone bad; under certain conditions they bring out their worst attributes.

Removal of affected plant material is part of the solution. Putting appropriate distances between host and parasite plants is another. Callery Pears are great trees for parking lots and streets where drier conditions prevent these fungal outbreaks. Systemic fungicide treatments are available. However, both groups of plants are fairly durable and recuperative. No matter how well they might look together their combination is just bad karma.

Plantings of Pears and Junipers are like the tit for tat relationship of Gertrude and Heathcliffe (if you’re not over 50 - look it up!). There is no real fatal flaw, but a lot of bumps and bruises along the way.

Please check out the linked article for more details.

Trellis Rust Management Update by Dr. David Roberts, MSU

Oh deer!

Whitetail deer are beautiful animals. It's surprising to see how successful they are in urban and suburban areas.

You'd better drive with caution, too, especially around dusk and dawn. And where there is one, there are usually others, so watch for deer number two or three to dart across the road. Car crashes are never good for anyone involved.

As nice as it is to see them up close, they come for one thing, to eat our landscapes. We have no one to blame but ourselves for invading their space.

So what can we do to protect our investment? Start by putting the gun down, your neighbor might complain about the holes in their garage.

There is a list of plants that are deer resistant in our new mobile app, but if you already have everything planted or can’t find the same look you want and need to plant those edible deer plants, there are products on the market you can apply to keep the deer out or limit the damage.

Christensen’s carries a couple of products that have been tested over the past 10+ years and have produced good results.

Deer Scram by Epic is a fine granular that is applied as a perimeter defense. This all natural, organic product is easy to use and does not have an offensive odor. The product will last 3-5 weeks before you need to reapply and it works year round. It has the added benefit of being a mild fertilizer.

Liquid Fence Deer & Rabbit Repellent is applied directly on the plants. It has an odor and taste the animals detest. This product will last 2-4 weeks depending on weather. The rain will dilute it quickly and it must be reapplied often.

Sometimes a physical barrier is required, so we also carry Deer Fence. It comes in a 7’ x 100’ roll and can be used to protect a large area.

Planting in heavy soils

Heavy clay soils are one of the toughest environments to plant in, but there are no hard and fast rules to follow. Whether the planting site is irrigated or not, and how much irrigation it’s receiving is crucial information. Here is an example: Concolor Firs will often decline and die in a heavily irrigated clay soil. In a lightly irrigated setting they will do fine.

Many planting guides will tell you to excavate 2-3 times the root ball diameter and amend the soil with top soil and peat moss. This is a big mistake! When you do this in a heavy clay soil you create a large “bathtub”, which can fill up with water in a heavy rain and drown your trees and shrubs. Digging a hole just large enough to hold the root ball reduces the amount of water around the plant.

Planting a little or a lot high to grade, depending on how wet the soil is, can be a good defense strategy. Just use a well-draining topsoil to feather out from the top of the ball to the top of the surrounding soil.

This columnar oak was planted at a correct depth in a raised bed. See below for a closer view.

One of the biggest mistakes I see is planting trees above grade on the top of a berm. Trees subjected to this treatment will almost surely die! Any rain (other than an all-day soaker), runs right off the berm. In this case create a shallow basin and plant below grade to capture those quarter to half inch mini rains.

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