pruning – The Garden Professors™

Why doesn’t my plant flower? Part 1

I often get horticulture questions from county extension agents, Green Industry professional, gardeners and my next door neighbors. One of the most common questions I get is why their plant did not flower that year. There are many reasons why a plant, either woody or herbaceous perennial, will not flower and both new and established plants can be affected. Some of the below reasons are obvious, some not so obvious.

There may be several reasons why a landscape plant does not flower (more to come next week):

Sun loving plants will not flower properly when grown in too much shade

1) Plants requiring full sun are not receiving enough sunlight.

Sun loving plants require at least six hours of direct sunlight per day to produce flower buds
Flowering is significantly reduced in areas with too much shade
Foliar diseases may be increased, such as powdery mildew, as foliage stays wet longer after rain
Growth is tall and “leggy” with most of the foliage and flowers occurring at the top of the plant

2) Transplant shock may result in little to no flowering 2-3 years after planting.

Transplant shock of 'Royal Red' Norway maple (Acer platanoides 'Royal Red') — Transplant shock of ‘Royal Red’ Norway maple (*Acer platanoides* ‘Royal Red’)

After planting, woody plants are using energy to establish a root system to support future leaves and flowers
Make sure plants are receiving enough water to encourage root growth and plant establishment
For trees, it may take longer than 3 years to produce new flowers

3) A plant may not flower because it is not cold hardy to your area.

Winter flower bud death on forsythia. Notice flowers at bottom of plant due to being under the snow line.

'Sunrise' forsythia blooms reliably each year in zone 4 — ‘Sunrise’ forsythia blooms reliably each year in zone 4

If you live in U.S.D.A. Cold Hardiness Zone 4 and plant is rated to only zone 5, buds may be killed over winter
For some plants, like forsythia, vegetative (leaf) buds can be a half to one zone more cold hardy than the flowering buds
Make sure to select a plant and cultivar rated to your cold hardiness zone

4) In warmer cold hardiness zones a plant may not receive enough chilling hours in winter to break dormancy.

'Dark Night' early flowering lilac (Syringa x hyacinthiflora 'Dark Night') has a low chilling hour requirement — ‘Dark Night’ early flowering lilac (*Syringa* x *hyacinthiflora* ‘Dark Night’) has a low chilling hour requirement

Chilling hours are the total amount of time during winter below a certain temperature, called vernalization
Required temperature are either below freezing, 0° C (32°F) or below 7°C (45°F) for temperate species
Plants suited for colder climates, like common lilac (Syringa vulgaris), require at least 3 months of cold temperatures in order to break dormancy and bloom in spring
In areas with mild winters, these plants may not flower or set fruit
Low chilling hour requiring plants are available for warmer areas
There is no definitive data on number of chilling hours required for all species

5) Severe late spring frosts can kill flower buds coming out of dormancy or emerging buds.

Late frost injury to new growth on boxwood (Buxus spp.) — Late frost injury to new growth on boxwood (*Buxus* spp.)

Developing spring buds are in advanced stages of development with minimal cold hardiness
Flowers can be killed or severely deformed
Especially damaging if the hard frost occurs after weeks of warm temperatures resulting in budbreak
Little to no fruit is produced that year; a serious problem for fruit growers

6) Pruning trees and shrubs at the wrong time of year will remove flower buds.

Beautiful flowers of Beauty of Moscow common lilac (Syringa vulgaris 'Krasavitsa Moskvy') — Beautiful flowers of Beauty of Moscow common lilac (*Syringa vulgaris* ‘Krasavitsa Moskvy’)

Flower buds are produced during the preceding summer for spring flowering plants
Prune within two weeks after flowering in spring
Avoid pruning in mid to late summer as next year’s flower buds are developing for next year’s bloom
Can prune large, suckering shrubs in dormant season, but realize flowering will be reduced that year
For summer flowering shrubs, late winter to early spring before growth begins is a great time to prune as flower buds have not developed yet for that summer

7) Flowering can decrease significantly on older, overgrown shrubs like lilacs, forsythias, chokeberries, and spirea.

Before renewal pruning of Chinese lilac (Syringa x chinensis). Notice larger diameter branches crowded together. — Before renewal pruning of Chinese lilac (*Syringa* x *chinensis*). Notice larger diameter branches crowded together.

After renewal pruning of Chinese lilac (Syringa x chinensis). Notice thinning of plant. — After renewal pruning of Chinese lilac (*Syringa* x *chinensis*). Notice thinning of plant.

Forsythia pruned as hedge copy — Shearing flowering shrubs into meatballs removes flower buds and destroys the natural arching habit

Larger diameter branches have reduced flowering as the stems age, especially for lilacs
Flowers may only be at the very top of the plant out of sight and smell
Large, suckering shrubs need renewal pruning, also called thinning
Depending on the species, every 1-3 years, remove about a third of the largest diameter branches (greater than 1.5” in diameter) back to the base of the plant to allow light penetration
Regeneration of new suckering branches will occur at the base of the plant that produce new flower buds the second or third year and fill in the plant
Thinning (renewal pruning) also preserves the overall plant shape
Never shear flowering shrubs as you will be removing flower buds and ruin the plant form
Renewal pruning should only be done for shrubs that sucker
Do not attempt this type of pruning on evergreens or slow growing plants

8) A tree or shrub may be alternate bearing with heavy blooming one year and sparse flowering the next year.

Sporadic flowering on CHINA SNOW Peking tree lilac (Syringa pekinensis 'Morton'). Many tree lilacs will flower heavily one year and sporadically the following year. — Sporadic flowering on CHINA SNOW® Peking tree lilac (*Syringa pekinensis* ‘Morton’). Many tree lilacs will flower heavily one year and sporadically the following year.

Common with some trees, such as Japanese and Peking tree lilacs (Syringa reticulata and S. pekinensis), and flowering crabapples (Malus spp.)
There is little a gardener can do to avoid this from occurring
If the fruit is not ornamental, removal of old flowers before fruit set may redirect a plant’s energy into flower bud production for next year’s bloom instead of fruit production this year
Select plants that reliably flower each year if you do not want to miss the show

Stay tuned for part 2 of this article next week!

Laura Jull, Ph.D. aka The Lorax

Pruning Overgrown Apple Trees

Ward Upham: Extension Blog Contributor
Extension Associate – Home Horticulture Rapid Response Coordinator
& Extension Master Gardener Coordinator
Kansas State University Extension
wupham@ksu.edu

Apple trees that are not pruned for several years will often produce so many branches that very little energy is left for fruit production. Overgrown apple trees are also difficult to harvest and spray. Gardeners who have such a tree are often at a loss as to how to get it back in shape.

Often the best (tongue-in-cheek) recommendation s for such a tree is to make one pruning cut at ground level and start over with a new tree. However, trees may have sentimental value that will make revitalization worth the time and effort. Realize that this will be a multi-year process because no more than 30 percent of the tree should be removed in one year. Here are some steps to follow:

Remove all dead wood. This does not count toward the 30 percent.
Remove suckers from the base of the tree.
Choose approximately six of the best branches to keep as scaffold branches. Remove all others. Branches should be cut flush to the branch collar. The collar is that natural swelling that occurs where a branch connects to the trunk or to a larger branch. Removing the collar would leave a larger wound that would take additional time to heal. Do not paint wounds. Research has shown that wounds heal more quickly if left open. Candidates for removal include branches with narrow crotch angles, which are more likely to break in wind and ice storms, and those that cross branches you will save. This may be all that is possible the first year if the 30 percent threshold has been reached.
Thin the branches on each scaffold branch. Remove crowded branches to open up the tree to light and allow humidity to escape. Shorten each scaffold branch by cutting back to a side branch. When you are through, the tree should have enough wood removed so that a softball can be thrown through the tree.

Severe pruning often will cause an apple to tree to produce vigorous side shoots from the trunk, called water sprouts. Main branches will also produce suckers that grow straight up. The suckers and water sprouts should be removed throughout the growing season so the center of the tree stays open.

In the case where a tree cannot be saved but you would like to preserve the apple tree variety, consider grafting. Scions taken from the old tree can be grafted onto a new rootstock to form a new tree. If you are not able to do so yourself, contact a local fruit tree nursery to find someone who may be able to help.

Pruning Overgrown Apple Trees pdf

Managing Diseases without Fungicides: A Focus on Sanitation (A Visiting Professor feature)

Submitted by:
Nicole Ward Gauthier, University of Kentucky Extension Plant Pathologist
PEOPLE: University of Kentucky Department of Plant Pathology Website
Kentucky Diseases of Fruit Crops, Ornamentals, & Forest Trees on Facebook
Amanda Sears, Kentucky Extension Horticulture Agent
Madison County Cooperative Extension Website

Alternatives to Fungicides

When diseases occur in urban landscapes, it is often presumed that fungicides are the most important and effective disease management tools available. However, a good sanitation program can help reduce the need for chemical controls and can improve the effectiveness of other practices for managing disease. This often-overlooked disease management tool reduces pathogen numbers and eliminates infective propagules (inoculum such as fungal spores (figure 1c) , bacterial cells; virus particles; and nematode eggs) that cause disease.

fig 1b marigold botrytis 1525420 (MC Shurtleff, UIll bugwd) (640x412) — Figure 1a. Marigold blossom infected with Botrytis

Figure 1b. Pathogen levels can build up on marigold flowers if diseased tissue is left in the landscape

close up of infecting spores — Figure 1c. Infecting spores on plant surface

Certain foliar fungal and bacterial leaf spots can become prevalent during rainy or humid growing seasons. When disease management is neglected, pathogen populations build-up and continue to increase as long as there is susceptible plant tissue available for infection and disease development (Figures 1a-c). Infected plant tissue infested soil and pathogen inoculum all serve as sources of pathogens that can later infect healthy plants.

Figure 2. Fallen leaves can serve as a source of inoculum (fungal spores) for additional infections. Many pathogens overwinter in fallen debris and then produce infective spores the following spring.

Reduction of pathogens by various sanitation practices can reduce both active and dormant pathogens. While actively growing plants can provide host tissue for pathogen multiplication, dead plant material (foliage, stems, roots) can harbor overwintering propagules for months or years (Figure 2).

These propagules can travel via air/wind currents, stick to shoes or tools, or move with contaminated soil or water droplets. Thus, prevention of spread of pathogens to healthy plants and the elimination of any disease-causing organisms from one season to another are the foundations for a disease management program using sanitation practices.

Sanitation Practices

Elimination and/or reduction of pathogens from the landscape results in fewer pathogen propagules. The following sanitary practices can reduce amounts of infectious pathogens:

Figure 3a. Cankers are common overwintering sites for disease-causing pathogens

Remove diseased plant tissues from infected plants. Prune branches with cankers (Figure 3a) well below the point of infection (Figure 3b). Cuts should be made at an intersecting branch. Rake and remove fallen buds, flowers, twigs, leaves, and needles.

Figure 3b. Remove infected branches, making cuts well below points of infection

Disinfest tools used to prune galls and cankers. Cutting blades should be dipped into a commercial sanitizer, 10% Lysol disinfectant, 10% bleach, or rubbing alcohol between each cut.
If using bleach, rinse and oil tools after completing work, to prevent corrosion.
Discard perennial and annual plants that are heavily infected and those with untreatable diseases (e.g. root rots, Figure 4; and vascular wilts). Dig up infected plants to include as much of the root system as possible, along with infested soil.

Figure 4. Heavily infected plants or those with untreatable diseases, such as black root rot (images left and right), should be removed from the landscape.

Trees and shrubs infected with systemic diseases (e.g. Dutch elm disease, Verticillium wilt, bacterial leaf scorch) that show considerable dieback should be cut and the stump removed or destroyed (e.g. by grinding).
If infected plants are to be treated with fungicides, prune or remove infected tissue (flowers, leaves) and debris to eliminate sources for spore production or propagule multiplication. This should be done before fungicide application. Fungicide effectiveness may be reduced when disease pressure is heavy, which can result when pathogen levels cannot be reduced sufficiently by chemical means (fungicides).
Discard fallen leaves, needles (Figure 5), prunings, and culled plants. Never leave diseased plant material in the landscape, as pathogens may continue to multiply by producing spores or other propagules. Infected plant material should be buried, burned, or removed with other yard waste.

pathogen 1 pathogen 2

Figure 5. Black fruiting structures of the pine needlecast pathogen contain spores (images left and right). Removal of infected plant tissue helps reduce amounts of inoculum in the landscape.

Do not compost diseased plant material or infested soil because incomplete composting (temperatures below 160˚ F) may result in survival of propagules.
Homeowners should be cautious about storing diseased limbs and trunks as firewood or using the woodchips as mulch. For example, wood from trees infected with Dutch elm disease should be debarked before placing in a firewood pile.
Remove weeds and volunteer plants to prevent establishment of a “green bridge” between plants. A green bridge allows pathogens to infect alternate hosts until a more suitable one becomes available. Be sure to remove aboveground parts AND roots.
Soil from container-grown plants should not be reused from one season to the next because pathogens can survive in soil.

Additional Resources:

University of Kentucky Extension Plant Pathology Publications

Photo credits:

R.K. Jones, North Carolina State University (Fig. 1A), courtesy Bugwood.org
M.C. Shurtleff, University of Illinois (Fig. 1B), courtesy Bugwood.org
David Cappaert, Michigan State University (Fig. 1C), courtesy Bugwood.org
Theodor D. Leininger, USDA Forest Service (Fig. 2), courtesy Bugwood.org
Joseph O’Brien, USDA Forest Service (Fig. 3, right), courtesy Bugwood.org
Elizabeth Bush, Virginia Tech (Fig. 4, left), courtesy Bugwood.org
Bruce Watt, University of Maine (Fig. 4, right), courtesy Bugwood.org
Andrej Kunca, National Forest Centre, Slovakia (Fig. 5, left), courtesy Bugwood.org
Robert L. Anderson, USDA Forest Service (Fig. 5, right), courtesy Bugwood.org
John R. Hartman, University of Kentucky (Fig. 3, left)

pdf Managing Diseases Without Fungicides

This gives “cutting the grass” a new meaning.

No, no, no.
NO.

Miscanthus sinensis, shaved into submission. — *Miscanthus sinensis* along the sidewalk in downtown Blacksburg, Virginia. Sheared into submission.

Textbook “right plant, wrong place.” Miscanthus sinensis is tough, drought tolerant, creates a nice screen, and if the late-blooming cultivars such as ‘Gracillimus’ and ‘Morning Light’ are selected, has little chance of seeding all over. After a few years in place, most cultivars are as wide (or wider) than they are tall. The lovely mounding/flowing habit is why this is the number one ornamental grass sold.

Mounded, rounded habit of Miscanthus as used at the Sarah P. Duke Garden (Durham N.C.). — Mounded, rounded habit of *Miscanthus* as used at the Sarah P. Duke Garden (Durham N.C.).

A better option – a very upright grass such as Calamagrostis x acutiflora ‘Karl Foerster.’ Regardless, this stuff needs to come out. Depending how long it’s been in the ground, a backhoe with probably be required. Or, they can continue carving it into a pillar.

The heartbreak of ‘Carrot-top’ syndrome

The perk of participating in a blog is you get a platform to vent on your pet peeves. Recently I’ve seen several classic examples of ‘Carrot-top’ syndrome. No, I’m not talking about the red-headed comic; though he tends to annoy me too.

Annoying Carrot-top #1.

The ‘Carrot-top’ I’m referring to occurs when white pine trees are sheared as Christmas trees but then planted as landscape trees. The typical result is that the side and lower branches remain suppressed while the terminals go crazy. I’m not sure why syndrome occurs in white pines and not other trees; it may be related to vigor of white pines and how hard the growers have to shear them to keep them in shape.

Annoying Carrot-top #2.

I love my friends in the nursery and Christmas tree industries and they work hard to grow quality trees, but this is one practice I’d like to see end. And, to be fair, they are giving customers what they want. If we set up a survey at a garden center and placed a 7’ sheared white pine next to a 7’ white pine that had been minimally pruned, 19 out of 20 people would take the tree that had been sheared to look like a Christmas tree. However, this is truly a case where less is more.

Random acts of horticultural violence

I’ve been traveling in Europe the past few days working on a project with some colleagues in the Czech Republic. While we typically think of our friends in Europe as being more progressive and cultured than us, it appears there are still a few areas where they have a ways to go – such as banning smoking from restaurants and bars – and in learning about the art and science of Arboriculture. (And before the hate mail from Europe starts pouring in; yes, I realize we can find plenty of scenes like this in the US – just hoped I’d find better on this side of the pond).

I’m not a big Forsythia fan, but really…?

Not sure what the desired outcome is here.

This is a black locust near Prague castle. Black locust, which is native to North America, was introduced to Europe for forestry planting in the 19^th Century. The trees were extremely well adapted and have become invasive in many parts of Europe, out-competing native trees and suppressing the development of understory plants. This particular specimen is one of the oldest in the Czech Republic, which presumably is the reason it has been allowed to linger on. A good example of when a tree’s quality of life has run its course. It truly pained me to look at this tree. And, of course, in the U.S. the tree would probably have been long gone due to liability concerns.

The tree is mostly hollow and was once cabled together. The cables were removed after the tree lost its tops in a storm 20 years ago.

It appears that the tree’s principle function these days is feeding woodpeckers.

OK, in the interest of international diplomacy, something Europeans get right is pollarding. In the U.S. what is passed off as pollarding is usually just topping. But when it’s done right (in this case with horseschestnut) and in the right setting (Prague Royal Gardens) it can create a striking effect.

Vote early and often!

In my last post I announced that we would be conducting the first landscape transplant experiment designed by social media. We have about 100 ‘Bloodgood’ plane trees in 25 gallon containers that are leftover from a recent nursery trial. The trees will be planted at our Hort station and receive minimal care after planting beyond an initial watering and a kiss for luck. I asked for some suggestions for potential treatments and got some good suggestions. Unfortunately, one thing I forgot to point out is that I have essentially no budget for this project. So trying to determine whether or not roots are mycorrhizal, or bringing in B&B trees for comparison, are beyond our capabilities at this juncture.

We did have some interest in determining the effects of manipulating rootballs for container-grown trees. These trees have been in pots for 2 years and I absolutely guarantee they are pot bound. Definitely a good opportunity to look at shaving or teasing rootballs.

There are a couple of other items that I am curious about.

One is crown reduction thinning. In forest nurseries trees are often top-pruned to reduce shoot-root ratio and increase transplant success. Obviously we would’t top landscape sized trees, but can selective pruning to reduce the ratio of crown area to root area reduce water stress and increase survival?

Along these lines, there is a lot of marketing of plant growth retardants to reduce transplanting stress. The most common is probably paclabutrazole – sold under various trade names including Cambistat http://www.treecaredirect.com/Cambistat-Tree-Growth-Regulator-p/3101.htm Does it work?

I’ve also been curious about hydrogels. I’ve long been a skeptic but have had several arborists tell me they’ve used them successfully – of course they didn’t leave an untreated control.

Then, of course, there’s Bioplex. http://www.bio-plex.com/pdfs/Bio-Plex2009Catalogue.pdf It might be easier to list what isn’t in Bioplex than what it contains. I suspect whatever effect it has is largely related to small amount of nutrients it contains.

Lastly, I still adhere to the notion that fertilizing trees at planting is not necessarily the source of all evil in the world and may even be a good thing. Here I get a chance to provide myself wrong and apply a dose of Osmocote in the planting hole.

OK that’s the background – time to vote. The link below should take you to a Survey Monkey survey. You can vote for more than one item, but please vote for no more than three.

http://www.surveymonkey.com/s/W3YGGSD

An unusual company

This week I’m in Charlotte, NC as a guest of Bartlett Tree Experts. In addition to providing tree services, this company also maintains the Bartlett Tree Research Laboratories and Arboretum. The latter includes over 300 acres of tree collections and ongoing research trials. Here’s a sampling of the tree research we had a chance to observe:

Demonstration espalier pruning…

…and pleaching

Comparison of root barrier materials. This area was covered with a sidewalk for a number of years and then exposed to observe tree rooting patterns. The purpose of the research was to find which barriers were most likely to prevent sidewalk lifting and cracking.

A control – no barrier, lots of roots!

Black plastic – lack of rigidity allows roots to grow over (and through) the plastic, then under the sidewalk.

18″ rigid root barrier. One of the more effective means of keeping roots out.

Removing circling roots before planting

A tree whose roots had been corrected before planting. I think this had been planted in 2007, then lifted a few weeks ago.

A tree without root correction. It didn’t grow any better than the corrected tree, and those circling roots are well on their way to becoming girdling roots.

This company employs a number of PhDs whose research is routinely published in arboricultural and horticultural journals. It was fun to finally meet these researchers whose work I’ve been following for years.

Wouldn’t it be great if more companies put this much effort towards research?

Tree terrors continue

You might remember back in October 2009 I gave one of the first Friday quizzes. The featured tree had epicormic shoots, and Monday’s answer revealed the neglected wire staking that was slowly girdling the main trunk. (Be sure you click on those links to see what the tree looked liked in 2009.)

I thought you might be interested to see what this tree looks like now:

A picture is worth a thousand words….many of those unprintable.

Update January 2022 – in response to a reader question, here is the tree in 2019 thanks to Google maps.

Unspeakeable Acts of Pruning

(Hey, I think it’s Tree Week on the GP!)

Our land has a nice buffer of big, old oaks, hickories, and maples between us and the two-lane highway. Power and phone lines thread through the middle of them. Thus, I have nightmares about orange Asplundh trucks.

So with much concern, I noted that utility crews and
subcontractors have been out in full force in our rural area,
inexplicably leaving one tree and then “pruning” another.

OMG that's awful

I pulled over and snapped this latest atrocity last night. The power lines are to the right (not in photo). As this is only a mere mile or two from our property, I may sit at home on the porch next week with the shotgun in my lap.