Rhododendrons are considered among the more difficult plants to trim. Many sources of information about pruning Rhododendron come from the Southern and Western states. The usual complaint about Rhododendron is that they get too large. That is not a big problem in the Midwest.

"Disbudding" refers to two aspects of pruning Rhododendrons. The first is simply removing spent blossoms. I’ve heard arguments over the years that, unless removed, the old flowerbuds will inhibit production of new flowers. I found absolutely no reference to this in my research travels. Also, to me this makes no sense. Mother nature put those flowers there and she can take them off – the shrub will bloom again! The best reason to remove them is one of aesthetics.

The second aspect of disbudding is pruning a Rhododendron for shape, compactness, and size of planting area allowed. Most pruning recommendations include removing dead or damaged branches as well as removing branches along the ground. These danglers can be more easily affected by fungus and can be a highway for weevils.

Now for the tough part – pruning a Rhododendron for shape and size. In essence, any pruning one does is shortening the distance between growth years. You can prune the current year’s growth back by hand right after blooming when the new growth is sticky or by mid-June with pruners when new growth has hardened off a bit. Pruning deeper on bare wood does not usually give good results. That limb will often die back or result in new shoots that may be spindly. One aside is my own observation that some of the newer grafted Rhododendrons are producing growth buds on low, woody branches which may develop if apical branches are damaged or removed.

Rhododendrons also include PJM types and Azaleas - both evergreen (kaempferi) and deciduous (Exbury and Northern Lights series). Most of the pruning rules are the same, however, you can prune much deeper into secondary wood and even lightly shear with good results. Compactness for shape is encouraged but avoid the meatball-effect. Also, hard pruning can reduce respiration and recovery.

Pruning aside, the best results for Rhododendron will be had from good soil preparation (i.e. moist, well-drained conditions), the addition of organic matter, and application of acid fertilizers.

Boxwood blight is a fungal disease of boxwood that results in the defoliation and decline of boxwood plants. Once it’s in the landscape it is very costly and difficult to control with fungicides. The boxwood blight fungus has a short life cycle and infections can spread quickly between plants, especially under humid, warm and wet conditions that favor disease development.

The main way that this disease is spread is through the movement of infected plants, cuttings, and boxwood debris. The sticky fungus spores are also spread on contaminated tools and equipment, worker's clothes, and water. The spores are unlikely to travel long distances through the wind. All plants infected with the fungus should be destroyed, as the chance of further spreading the fungus is highly probable. Limiting the spread of this sticky fungus is very difficult and can only be accomplished by following good sanitation practices.

Boxwood blight has been found in Michigan. Because of this we will NOT accept any returns on boxwood once they have left the nursery. We will also ask that you do not bring any boxwood plants, leaf litter, or clippings into our nursery. We reserve the right to not load any vehicle that has boxwood or debris from outside of our nursery. Please do not bring in any samples of boxwood that you are trying to match - take several pictures of the plant you are trying to match and we will help the best we can.

Boxwood blight can look like many other issues that boxwood can have, such as leaf spot, winter burn, and other non-threatening fungal diseases. This means that:

The only way to confirm whether a plant has boxwood blight is to submit samples to a professional plant disease diagnostic lab.

...and I don't mean cider or donuts. No, it's COLOR TIME! 

Mums. Burning bush. Maple trees! You can probably name a dozen fall color plants without even thinking about it. But what about choosing from some of the lesser-known plants that also shine every autumn? Here are my top ten favorite fall color plants that may not be on your radar.

• Hydrangea quercifolia and cultivars: The large, rough-textured leaves are especially striking as they turn shades of red and purple every fall.
• Viburnum x juddii: Beloved for it's sweetly-scented spring flowers, this medium-sized shrub has great burgundy-purple fall color accented by blue to black berries.

• Itea virginica cultivars: This medium-sized native shrub deserves to be planted more often. The orange, red and burgundy fall color is outstanding and is extremely long lasting.
• Epimedium cultivars: An underused perennial tolerant of dry shade that gets brilliant red to purple fall colors.
• Amsonia hubrectii: This North American native perennial grows to about 3x3'. The fine, feathery foliage turns a striking golden-yellow in the fall.
• Clethra alnifolia ‘Hummingbird’: Usually planted for the amazingly fragrant flower spikes in mid-to-late summer, this smallish shrub turns a gorgeous golden yellow each fall.

• Fothergilla ‘Mount Airy’: This is a handsome 3-5’ shrub that gets wonderful fall color in hues of red-purple, orange and yellow.
• Amelanchier: OK, so this one is not that obscure but it has to be in my top ten.
• Vaccinium hybrids: These ericaceous shrubs (best known are blueberries) will surprise you with their beautiful red-orange fall color.
• Panicum virgatum cultivars: ‘Shenandoah’ and ‘Hot Rod’ are two that turn beautiful red or burgundy.

Various parts of the country are known for their vibrant displays of fall foliage colors, none more so than the Midwest, and in particular, Michigan. It seems odd that we get such joy from the annual death of leaves from deciduous trees, shrubs, and even some perennials. Why do leaves change colors in the fall, and why can’t we guarantee that fall color to our customers?

I'm going to super-simplify the scientific part of this explanation so here goes:

• Chlorophyll produces carbohydrates (sugars) plants need for growth and is responsible for the green color in leaves and stems.
• Carotenoids express as yellow and orange and are generated during the growing season alongside the green.
• Anthocyanins are only produced in the fall after sugars are trapped in the leaves, and create reds and purples. More reds, and earlier reds, can come from plant stresses, low nutrition, and near-but-not freezing temperatures. Freezing stops the process of making red pigments.

During spring and summer chlorophyll masks the other pigments so you pretty much just see green, however shorter days, longer nights, and cooler temperatures trigger an abscission layer to form, cutting off the flow of sugars and replacement chlorophyll. As the green color fades, the underlying yellow and orange colors are revealed, and reds and purples develop. Eventually all the colors break down, leaving brown tannins.

What colors are produced, and in what amounts, and when in relation to other plants, is due to the genetics of a particular plant, growing conditions, and weather.

Similar environmental conditions as those causing red color in leaves also may cause fall colors to come sooner, or later, or to last longer some years than others. Drought during spring and early summer may signal the plant to form the abscission layer early, shutting down growth and causing color change sooner than usual.

So while moisture is good earlier in the season, too much late in the season means more clouds, less sun, and more muted colors. Too much rain in fall plus strong winds, may cause many leaves to fall prematurely. Cooler temperatures in late summer, and plenty of sunshine, often leads to brighter colors sooner. Cool is good, but too cold (freezing) can be bad, killing leaves early.

So ideal for fall color would be a moist growing season early, dry late summer and early fall, with sunny warm days and cool nights during the latter.

Choosing cultivars with known fall color-producing ability will certainly help, but as you can see there are other factors that come into play, and you really cannot guarantee fall color.

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)

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!

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)

Guess what! We sell these! I don’t care how you say ‘em or spell ‘em as long as your check clears. I’m pretty sure my boss would agree with me. Hardly a day goes by that we don’t get contractor lists of hybridized and spell-’em-as-you-hear-’em names. I personally love the challenge! And yes, we do sell junipers - and yews.

In particular, Christensen’s sells a number of species of upright Junipers, the Eastern Redcedar. They are somewhat interchangeable with Arborvitae. Junipers require and tolerate hot, dry, sunny conditions but can have difficulties in poorly drained areas. They can be planted as backdrop accent evergreens or hedged into a living fence. A caveat is to avoid planting them too close to some members of the Rose family such as Crabs, Pears, Hawthorn, and Quince due to host/parasite rust occurrences.

The species of Juniperus that Christensen’s typically stocks are:

J. virginiana

• ‘Keteleer’ - a soft, green needle with loose habit; often used for native plantings
• ‘Taylor’ - a newer introduction with a bluish-green, tight habit; similar in form to Thuja occ. ‘Emerald Green’

J. chinensis

• ‘Blue Point’ - a bluish-green, full habit; often used for topiary
• ‘Hetz Columnaris’ - green needles with broad, architectual habit; best of the fruiting varieties we stock
• ‘Spartan’ - a green needled variey with a tight, upright habit

J. scopulorum (Rocky Mountain Junipers)

• ‘Blue Arrow’ - a soft, bluish upright with a very tight form
• ‘Skyrocket’ -a grayish, green variey similar in form to ‘Blue Arrow’
• ‘Wichita Blue’ - a broad, very blue form with very soft growth, but a rugged look

Availability for this genus is not quite as reliable as Arborvitae. We usually see periodic waves of uprights appear throughout the season. Junipers do, however, offer a greater range of color when compared to Arborvitae.

Next time you need an upright evergreen, ask to see some of the varieties just mentioned. Exact spelling not required!

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.

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.

Horticulturally speaking, the color blue is rare. So rare, that many of the flowers we call "blue" are in fact... purple. Blue iris? Purple. Blue roses? HA! Purple - and weak at that. Syringa, Campanula, Lobelia, Hyacinth, Baptisia... all have varieties CALLED blue, but they are... purple. I found this quite confusing when I started in the nursery business. Apparently we gardeners are DESPERATE for blue in the garden and we will call anything close "blue".

This tendency extends to foliage as well - blue spruce, blue juniper, and blue hosta, are all rather more silvery than blue, with the added insult of the color wearing off with weather and time! I still chuckle about the customer I had on the retail lot one day, who accused us of spray-painting the 'Moerheim' spruce because, "Look! It rubs off!" There wasn't much I could say because he was right, it did.

There ARE a few truly blue flowers we can grow in Michigan. Amsonia, Delphinium, Virginia Bluebells, the annual 'Black and Blue' Salvia, Forget-me-nots, Sisyrinchium, and Ceratostigma all have excellent blue flowers. Scilla siberica is a minor bulb that naturalizes and can give you an ocean of blue flowers every spring. Chionodoxa's pretty good, too.

In shrubs you can try Caryopteris - wait, that one's a bit on the purple side - heck, it's barely a shrub, more like a woody perennial. Hmmmm. Hibiscus 'Blue Chiffon' is pretty blue. Almost. OKAY, OKAY, FINE. You want blue? You'd best be planting Hydrangea. The old favorite, 'Nikko Blue' has been surpassed by newer cultivars like Nantucket Blue™ and The Endless Summer® line, with the original Endless Summer®, Twist-n-Shout®, and BloomStruck®  all of which bloom on both old and new wood. These plants can be coaxed into producing nice blue blooms with the proper soil pH.

So you do have some options. And take those photos of bright blue-flowering plants on Pinterest with a grain of salt. Most of them are Photoshop. Or perhaps dyed like those poor Phalenopsis orchids at the grocery store.