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K-State Turf and Landscape Blog

Tag: ornamentals

Historic Dry Spells Lead to Tree Stress: Help Ensure Your Trees Are Healthy Enough to Handle It

Posted on by Teresa Roberts

By Jason Griffin, Professor, Extension Specialist

Extension personnel across the state have been answering questions about dying/dead trees and shrubs since early spring. Symptoms have ranged from dead, to partially dead, to unusual growth, and late leaf emergence. While it is always good to scout for damaging insects (bagworms anyone?), disease pathogens, and physical injuries such as repeated mower damage to the trunk or recent construction projects that compromised root systems, this year we can blame a lot on our old friend mother nature. Since late summer 2022 through May 2023 rainfall has been scarce, a hard freeze came early, and summer heat exposed any weak landscape plants.

The National Weather Service office in Wichita (@NWSWichita) describes the
period from July 1, 2022 to April 23, 2023 as the 5th driest in history and the driest since 1989. Under those conditions, trees fail to accumulate adequate carbohydrates for the approaching winter, making them more susceptible to winter injury.

As drought continues through winter and spring, trees lack adequate moisture required for new spring growth. The result is trees failing to leaf out in the spring or pushing new spring growth that looks abnormal. If the plants were compromised by pests or physical injuries, environmental stress effects are magnified.

Trees do have mechanisms to deal with elevated temperatures. Unfortunately for the plants, heat rarely occurs as a single isolated event, and it is impossible to talk about heat without mentioning its partners in crime. As seasonal temperatures rise, precipitation becomes less frequent (or absent). Additionally, the Kansas wind machine gets fired up and cloud cover becomes less abundant.  This quadruple whammy reduces a plant’s ability to tolerate elevated temperatures. Trees and shrubs use transpiration to cool themselves. When soil moisture is lacking, transpiration is reduced, thereby exacerbating the issue. If the situation does not improve, long-term damage can occur. What we see now are the effects of months of drought, a cold winter, and summer heat.

Of course, most plants made it into 2023 with little noticeable difficulties, attesting to their resiliency. What can be done to reduce the stressors that lead to tree decline?

Watering Landscape Ornamentals

Posted on by Brooke Garcia

By Dr. Cheryl Boyer

It’s that time of the year when it’s both very hot and, likely, very dry. While it’s important to water landscape ornamentals all year long, now is a critical time to make sure plants have all the resources they need.

We have several publications about best practices for watering:

Newly planted trees (within their first year) should be watered at least weekly but check the soil to make sure it’s draining well. Slow-release watering methods like micro-pore bags and 5-gallon buckets with small (1/8-inch) drainage holes are a good way to apply irrigation to trees and some shrubs. However, remember to remove the bags when they are empty to ensure good airflow around plant stems and reduce pests and diseases. Removing turfgrass and other ornamental plants to at least the tree dripline (or beyond) will help trees access more water and grow more quickly—make sure to mulch the turfgrass-free zone to help retain applied water.

Established trees will benefit from a thorough soaking (to a depth of 12 inches out to and beyond the drip line) every 3 to 4 weeks. Established shrubs need water every 2 to 3 weeks during this drought- and heat-prone time of year. Plants growing in raised beds and berms may need to be watered every 1 to 2 weeks. Soaker hoses work well for watering established trees and shrubs.

You may want to consider taking advantage of a light rainfall (if you get one in July and August) by watering immediately afterward to help moisture move deeper into the root zone.

Any way you slice it, watering is a good thing. There are many other factors to consider for successful planting, but right now watering is top of the list. Keep it up—plants are thirsty just like you!

Flower garden sanitation to improve plant health next spring

Posted on by kennelly

Many plant pathogens like to survive the winter in infected crop debris. One example is iris leaf spot.

 

Here is a zoom – the black spots are structures where the fungus produces spores:

So what can we do? Here are some tips from the Horticulture News (http://www.ksuhortnewsletter.org/):

Iris are known for a couple of common problems: a fungus disease known as iris leaf spot and an insect named iris borer. Though both cause problems in the spring, now is the time to start control measures. Both the fungus and eggs of the borer overwinter on old, dead leaves. Remove dead leaves and cut back healthy leaves by ½ this fall to reduce populations of these pests. Also remove other garden debris from the iris bed.  This can significantly cut down on problems next spring. (Ward Upham)

Another disease that lurks over the winter is peony leaf blotch (also known as red spot or measles) and you can find info on that disease here on the Common Plant Problems website.

 

 

(Photos by Megan Kennelly)

Pruning Trees and Shrubs in the Fall

Posted on by kennelly

(Ward Upham, KSU Horticulture & Natural Resources. Original source: http://www.ksuhortnewsletter.org/)

 

Pruning in August can stimulate new growth that is less hardy during the winter.  But what about pruning at this time of year?

Woody plants move sugars and other materials from the leaves to storage places in the woody portions of the plant just prior to leaf fall and we would like to maximize those stored energy reserves.  Even pruning later in the fall can cause a problem by reducing the cold hardiness of woody plants.  Dr. Rich Marini at Penn State Extension has written , “Based on everything that has been published we can conclude that woody plants do not attain maximum cold hardiness when they are pruned in the fall. Trees are affected more by heavy pruning than light pruning.”  However, this does not mean that woody plants pruned in the fall will necessarily suffer winter damage.  In most cases, I think you can get away with the old adage of “prune whenever your pruners are sharp.”  However, damage can occur if we have a sharp drop in temperature before plants are completely hardened off.  Also, marginally hardy plants are more susceptible to winter damage, especially if pruned in the fall.  Though light pruning and removal of dead wood are fine this time of year, you may want to delay severe pruning until spring.

Consider pruning to be “light” if 10% of less of the plant is removed. Dead wood does not count in this calculation.  Keep in mind that even light pruning of spring-blooming shrubs such as lilac and forsythia will reduce flowers for next year. We normally recommend that spring-bloomers be pruned after flowering.

Shrubs differ in how severely they can be cutback. Junipers do not break bud from within the plant and therefore should be trimmed lightly if you wish to keep the full shape. Overgrown junipers should be removed. On the other hand, there are certain shrubs that can be pruned back severely during the spring. Rejuvenation is the most severe type of pruning and may be used on multi-stem shrubs that have become too large with too many old branches to justify saving the younger canes. All stems are cut back to 3- to 5-inch stubs. This works well for spirea, forsythia, pyracantha, ninebark, Russian almond, sweet mock orange, shrub roses, and flowering quince. Just remember that spring is the correct time to do this, not now.

(Ward Upham)

Iris leaf spot – spring cleaning to disrupt fungal life cycle

Posted on by kennelly

(Megan Kennelly, KSU Plant Pathology)

Irises are a popular plant, often grown in large groups. Iris leaf spot is a fungus that can cause mild spotting to severe dieback.The fungus spreads by spores that are dispersed in wet weather.

Red-brown spots with yellow halo:

A closer view – the black bumps are spore-producing structures:

 

Another close-up view of one spot:

Spots can coalesce to cover a large area

More significant dieback:

Where does that fungus spend the winter? In old infected leaves. Get those outta there to reduce your risk of infection in the new year. Clearing out old infected plant tissue breaks the life cycle.

More information about managing iris leaf spot is available in a recent article by Ward Upham in the KSU Horticulture News

 

Goldilocks and the three trees. (Site conditions that are “just right.”)

Posted on by kennelly

When it comes to trees:

Trees need water. Not too much, not too little, but just right.

Trees need appropriate temperature. Not too hot, not too cold, but just right.

Trees need to prune. Not too much, not too little, but just right.

If you are looking for some cozy winter reading, you can check out our publication about Tree and Shrub Problems in Kansas.

In addition, I just came across a great publication from University of Kentucky that discusses tree and shrub decline. The information is similar to parts of the Tree and Shrub Problems in Kansas book, but sometimes it is helpful to read information from a new source since everyone presents information in a slightly different way. The reference is Stress and Decline in Woody Plants.

Happy reading!

 

 

Fall care of peonies

Posted on by kennelly

I love peonies! I’m lucky to have a neighbor down the street with an amazing display every spring.

Peonies do need some attention, though, including cutting them back. One reason to cut them back is to remove leaves infected with “peony measles.” By removing infecting the leaves from the site you can disrupt the life cycle. The fungus survives year-to-year in infected leaves, so removing them reduces infection risk next year.

peony-measles-ward-ipmimages

(Photo by Ward Upham)

 

Here are some tips from Ward Upham from the Kansas Horticulture News:

 

Cut peony foliage back to the ground if this hasn’t been done already. Compost or discard foliage. Fertilize peonies twice a year — in the spring shortly before new growth appears and then again in the fall after the plants have been cut back. A total of 1.5 to 2 ounces (3 to 4 tablespoons) of a 1-1-1 fertilizer such as a 10-10-10 or 13-13-13 per plant per application should be used. This amounts to 3 to 4 ounces of fertilizer per year. If a soil test reveals adequate levels of phosphorus and potassium, use a lawn fertilizer such as a 29-5-4, 27-3-3 or something similar, but cut the rate to 1/3 of the above rate. In other words apply ½ to 3/4 ounce (1 to 1.5 tablespoons) per plant. The lawn fertilizer should not be a “weed and feed.”
Never apply fertilizer directly on the center of the peony as the buds (eyes) may be damaged. Rather, place the fertilizer in a band from 8 to 18 inches from the center of the plant.  Water the fertilizer in so the plant can take it up.
Winter protection of herbaceous peonies is only necessary the first winter after planting to prevent alternate freezing and thawing from lifting plants out of the soil. A couple of inches of mulch should be sufficient. Any organic material that does not mat down will work and should be applied after the ground freezes. Avoid using leaves that will mat together. Remove the covering before growth begins in the spring.
The less common tree peonies have woody stems like deciduous shrubs and should not be cut back to the ground or pruned in the fall. Collect the shed leaves and place in the compost pile this fall. Though tree peonies are hardy to Zone 4, they do benefit from a light mulching over winter. Also, it is recommended that tree peonies be fertilized during November to get the plants off to a good start next spring. It is best to take a soil test to see what nutrients are needed. If the soil needs phosphorus and potassium, use a complete fertilizer (such as 10-10-10, 9-9-6, etc.) at the rate of 2.5 pounds per 100 square feet. This would equal 1 rounded teaspoon per square foot.
If phosphorus and potassium are not needed, blood meal makes an excellent fertilizer. Apply at the rate of 2 pounds per 100 square feet or 1 teaspoon per square foot. Turf fertilizers such as a 27-3-3 or 30-3-3 also can be used but at the rate of to 1 pound per 100 square feet or 1 teaspoon per 2 square feet.