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.

You’ve just installed your plant material and now it’s time to decide which material to use to cover the soil. The two most common materials are mulch and stone. Aesthetic preferences aside, here are some pros and cons for each.

We’ll start with stone. Starting with the pros, stone does not break down and need replacing. Also, you have few issues with weeds initially due to the use of weed barrier fabric. One of the problems with stone is that it is much more expensive to install, though some would argue that the upfront costs are offset by the fact that it doesn’t have to be replaced annually.

The primary issues are maintenance. Though weed barrier is effective in the short term, eventually a layer of dust and plant material create a medium on top of the fabric that weeds can and will grow in. This can be mitigated somewhat by careful cleaning of the beds (the heavier the stone the better for cleaning), but eventually weeds will become a real problem.

Physically removing weeds is difficult. Chemical removal is an option, but then you still have to struggle to remove them once they’ve died. Also, stone does not benefit the landscape planting in any way, and though weed barrier fabric is designed to allow water to get through, if there is any kind of slope, more water will run off than soak in compared to not using it. Over time the fabric may degrade or show through, then you can have a real mess.

Also, stone in a sunny location can get uncomfortably hot for some plants. Adding or removing plants, as well as working on irrigation, becomes more difficult in a stone bed. For many though, the aesthetic value is worth any complications.

With mulch, I will start with the cons. It does have to be replaced as it breaks down. If you replace it yearly for aesthetic reasons, the old mulch might need to be removed to prevent a harmful build up. We've all seen towering cones of much piled against tree trunks, and it is not a good thing.

If you wait for it decompose sufficiently, removal of the old mulch may not be necessary. Mulch is also susceptible to more weed growth initially than stone, though the weeds are easier to remove physically. Mulch can become matted as the season progresses causing some water runoff, but a quick fluffing or cultivating of the mulch will break up mats to restore proper absorption. The best thing about mulch is its benefit to the plant material.

Mulch is good for water retention in the soil, provided there’s enough water to permeate the mulch in the first place. Mulch also provides a good environment for beneficial insects, fungi, and microbes in the soil. Some amount of nutrients are also made available to the plants as the mulch decomposes. Mulch also provides insulation for plant roots that is effective in hot and cold conditions.

It is a waste of money to use weed barrier fabric under mulch as you are defeating the purpose by immediately placing a medium in which weeds can grow on top of it.

Stone or mulch? The final decision I leave to you.

For those of you who don’t know, I have been a hairdresser for almost 35 years (...yes, I started VERY young). With the clientele I still maintain, spring is the time of year my customers want "a little more off the top". It's the time of year temperatures change and HUMIDITY can alter the decision of a new spring 'do. It’s kind of the same with my roses! 

Here at CPC, and for you and your customers, spring is the best time for cleaning up, shearing up, and shaping up your roses. After the snow is gone but before new leaves start to pop, it's the perfect time to give these beauties a bit of attention for top performance. While we are all looking forward to color and growth in our landscape, nothing holds court like a well-maintained rose bush.

Just as I cut off fried hair and split ends while styling my clients, when cleaning up roses I begin by removing last year's old leaves from on and around the plants. This reduces pests or disease carried over from last season. You'll want to cut back dead wood, broken or crossing branches, and anything smaller than a straw. It might seem like giving a pixie cut when you're going for long layers, but clearing out all this extra branching allows for better airflow - and airflow is key for keeping rose foliage healthy.  When trimming the remaining branches, cutting above outward facing buds directs the growth upward and outward for a more optimal vase-shaped form.

Knock Out® roses are considered a shrub rose and self-cleaning. However, they still benefit from a nice cleanup in the spring, especially after they've had a few years in the ground. I like to take them down to about 12-18". They are such vigorous growers that, if you don't show them who's boss, you'll find yourself with a plant much larger than you intended.

Climbing roses are a little different. They have main, upright branches and lateral ones. The main branches should be left alone as much as possible. If cut, the plant will focus it’s energy on recovering height before pushing out lateral growth, which is where you'll get flowers. When pruning lateral branching there is no worry where to cut around the buds, anywhere will encourage a push of new growth and those desirable flowers.

So have no fear when considering your spring maintenance program. Sharpen those tools and get pruning! Oh, and don't forget your gloves.

You’ll never really know your profits for this year until you finish your replacements next year! Winter protection can help reduce these.  Although we don’t mind selling you replacement plants, we do want your business to be as successful as possible

Three common practices we have covered in previous articles are applying Wilt Pruf on your broadleaf evergreens, putting up burlap screens as barriers to salt and wind, and using bark protectors to prevent deer and rabbit damage. There are two other recommendations I can give you.

Preventing frost cracks. Previous minor wounds, scuffs or scrapes on a tree trunk even when healed react differently to expansion and contraction from freezing and thawing repeatedly during the winter. The wood can split right open, sometimes with a sound like a rifle shot. This commonly happens on the sunny south or west side of the tree. One way to prevent this is to apply tree wrap each fall. This is a 4” wide waterproof, crinkled paper that you wrap around the trunks of young, thin-barked trees to protect from both sunscald and moisture loss. The death of the sap-carrying tissue from cracks or cankers can cause a surprising amount of damage higher up the tree. The tree wrap should be removed in the spring.

Provide adequate moisture. You may say “The plant has lost its leaves, why do I still need to water?” You may not realize that the optimum time for roots to grow is the fall season, right up until the ground freezes, which in some years is not until January. We often get rain this time of year but newly planted trees often need supplemental watering while they are replacing roots lost from being moved. 

Even during winter months plant roots continue to replace moisture lost to drying winds and sun. Evergreens, both needled and broadleaved are particularly vulnerable. Plants that take up enough water will have the best chance to survive our winters and be ready for the spring push. 

So water well, and mulch those beds to prevent desiccation during those below freezing weeks and hopefully your landscape jobs will look as good in the spring as they did when you installed them.

​Does Frost Really Crack Trees? by Michael Snyder​​​

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)

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.