Care and How-To Articles - Trees and Shrubs
Shedding, peeling, or splitting bark on trees in the landscape can be a concerning sight.
Understanding what is causing the bark loss is an important first step to preventing further damage in the future.
Summer is often the time of year Phytophthora root rot starts showing up in rhododendron and azalea plantings. The fungus is favored under extremely wet conditions and in heavy, poorly drained soils. The wet spring may have aggravated the condition more this year.
Phytophthora root rot of rhododendrons is caused by several species of Phytophthora. The pathogens, primarily P. connamoni, P. citriocola and P. cactorum, are soilborne and invade roots under wet conditions. Most cultivars of rhododendrons are highly susceptible to attack by Phytophthora.
Many trees and shrubs thrive in Iowa's fertile, well-drained soils. Most trees and shrubs, however, don't like wet soils. Fortunately, some plants tolerate wet soils better than others.
When selecting trees and shrubs for the home landscape, gardeners should select plants suitable for the site. Wet sites can be a challenge. However, the trees and shrubs listed below will perform well in wet soils.
When selecting annuals, perennials, shrubs, and trees, choose plants that are adapted to the growing conditions at the planting site. Most landscape plants prefer moist, well-drained soils in full sun. However, there are plants that will tolerate more difficult sites.
Lists of annuals, perennials, shrubs, and trees that tolerate dry soils, wet soils, and partial shade are provided below.
Some individuals consider shady sites to be problem areas in the home landscape. However, shady areas actually provide opportunities for home gardeners. Wise plant selection can turn a shady site into an attractive landscape area. A number of trees and shrubs can be successfully grown in partial shade. (Partially shaded sites receive 3 to 4 hours of direct sun but are in shade the rest of the day.)
Selecting and planting shade tolerant trees and shrubs, along with suitable annuals and perennials, can transform bare shady areas into attractive landscape sites. Below is a list and brief description of trees and shrubs adapted to partial shade.
Many plants grown in the home landscape require consistent moisture throughout the growing season without staying too wet. However, there are a few annuals, perennials, shrubs, and trees that perform well in wet soil conditions. This includes low-lying areas, water edges, or soils with poor drainage. Many of these plants will also tolerate periodic flooding.
Many plants grown in the home landscape require consistent moisture throughout the growing season. However, there are a few annuals, perennials, shrubs, and trees that perform well in dry weather or dry soil conditions. All of these drought-tolerant plants will require water initially to establish a good root system. Once established, however, they require little watering and will make it through the driest of years with little damage.
This page highlights shade tree options well-suited for the Iowa landscape. While it doesn't include every possibility, this list provides descriptions of many wonderful species and cultivars proven to be good options for many Iowa homeowners.
Occasionally the need arises to move shrubs within the landscape. Follow the tips below to have the best success moving deciduous shrubs like lilac, viburnum, dogwood, ninebark, panicle hydrangea, and others.
When to Transplant
Early spring (before growth begins) and fall (after leaf drop) are the best times to transplant deciduous shrubs.
How to Transplant
Shrubs are best moved with a ball of soil adhering to the roots. With a portion of the root system intact, transplanting shock should be minimized with faster reestablishment.
The soil should be moist when the shrub is dug. If the soil is dry, thoroughly water the area 3 to 4 days before digging the plant.
For some shrubs, taking cuttings is not successful as propagules may die before new roots can be formed. In these cases, layering is another option.
Layering is a form of propagation where new roots are formed on vegetative pieces (primarily stems) while the propagule is still attached to the parent plant. This form of propagation produces propagules that are genetic clones so your propagule will be the exact same plant as the parent plant with the same flower color, form, and other attributes. This form of propagation can be time-consuming, but because plants are supported by the parent plant while developing new roots, it is relatively low stress on the plant and has a good rate of success for home gardeners.
Several factors cause branch dieback on trees. Correctly diagnosing the problem(s) is the first step in managing an unhealthy tree. Below are some common causes of branch dieback on trees in the landscape. Use this guide to evaluate your tree and determine the likely cause of the branch dieback.
Stem girdling roots happen when a tree’s own roots either completely encircle the trunk or grow tangential to the trunk on one or more sides, causing stem compression and damaging important vascular connections (xylem and phloem). Learn more about how to address this all too common issue with trees in the landscape.
Buckeyes and horsechestnuts are members of the genus Aesculus. The true chestnuts are members of a different genus - Castanea. Members of the genus Aesculus have palmate leaves – meaning they have 5-7 leaflets that fan out like fingers on your palm. They have showy flowers in spring, which mature to large dark brown capsules in late summer or early fall. While the hard, shiny buckeye fruits are considered good luck when carried in your pocket, they should not be eaten since they are poisonous to people.
Overall, lilacs are easy to care for and problem-free shrubs. Occasionally, problems arise like failure to bloom, flowers opening out of season, powdery mildew, and other disease or insect issues.
More information about common lilac problems and how to manage them is presented below.
Lilacs offer gardeners a large variety of plant shapes, sizes, and flower colors. Hybridizers have worked extensively with the common lilac resulting in over 1000 different varieties. There are seven color classifications for lilacs: white, pink, violet, blue, magenta (reddish-purple), lilac, and purple. Flowers are also available in single and double forms.
Below are several species of lilac that grow in Iowa. They are roughly listed by bloom time from earliest to latest.
“What tree should I plant in my yard?” is perhaps one of the most frequent questions we get. It’s a perfectly legitimate question, but one that can be difficult to answer. Difficult because there are so many choices, and the fact that not every tree will succeed in every landscape situation. It’s a little bit like choosing a companion animal (dog, for example) for your family. There are an endless array of breeds, but not all will be suitable for any given family unit. Similarly, trees must be matched to the site. Spatial, environmental, and aesthetic needs and features top the list of important considerations.
The Colorado spruce does not do well in the less-than-ideal growing conditions of Iowa's hot, humid summers. Here are alternatives to consider.
Your smartphones can be wonderful tools, and several apps on our phones can help with plant identification. These apps are best utilized to aid in identification rather than as a tool to definitively identify the plant. Learn more about how to best utilize these convenient tools for plant identification.
While many woody trees and shrubs bloom in the spring, there are several great selections for Iowa that look their best in June, July, and August. Consider these shrubs to add color and interest to the garden in the summer.
Trees are valuable additions to the home landscape. When problems arise with the health of a tree, it can be difficult to determine what is causing the issue.
Occasionally the need arises to move trees within the home landscape. Follow these tips to move small, young trees successfully.
When to Transplant Trees
Early spring (before growth begins) and fall (after leaf drop) are the best times to transplant deciduous trees. Evergreens are most successfully transplanted in early spring and late summer (late August to mid-September).
How Large Can the Tree Be?
Home gardeners should limit themselves to transplanting trees with a trunk diameter of 2 inches or less. Trees with a trunk diameter greater than 2 inches should be moved by an experienced landscape contractor or nursery professional.
The weather can be erratic as it transitions from autumn to winter and again from winter to spring. It is common to have below freezing temperatures in late September or early October followed by a stretch of a week or more of warmer temperatures. When this temperature dip happens, protecting plants can be beneficial, allowing to continue harvest and enjoy them in your garden longer.
It is also common to have a period of warmer temperatures in late March or early April that can bring plants out of dormancy followed by below freezing temperatures that can potentially damage the new growth or emerging flowers.
Trees, shrubs, roses, and perennials are available bare root. That is, they come to you from the garden center or mail-order retailer with no soil around their roots. Extra care is required to make bare root plants survive and thrive.
As winter fades and spring arrives, several things can be done to prepare the garden for the upcoming growing season.
Below are tips for the perennial garden, vegetable garden, annual containers, trees & shrubs, and lawns.
Gardeners can brighten up the last few weeks of winter by forcing branches of flowering trees and shrubs indoors. Forsythias, pussywillows, serviceberries, crabapples, magnolias, redbuds, and many fruit trees can be coaxed into early bloom indoors, helping revive the spirits of winter-weary Iowans.
Manure is the oldest fertilizer known to civilization and can be a cost-effective soil amendment with many beneficial qualities. Many gardeners feel manure is superior to synthetic products. Careful and appropriate use of manure, especially in vegetable gardens, is important.
Iowa soils are very diverse and so are the chemical characteristics that make up these soils. Soil pH is one property that can vary widely across the state both naturally and due to how we manage the field or garden. It is also one of the most cost effective and easy to manage soil properties that can be modified to improve plant health and crop production.
Learn about how to decrease and increase your soil pH below.
February and March is the best time to prune most trees and shrubs in Iowa. The absence of foliage at this time of year gives you a clear view of the tree and allows the selection and removal of appropriate branches. Also, when pruned in the late dormant season the walling-off, compartmentalization, or sealing of wounds can begin as soon as growth starts in the spring giving the tree the most time to recover from the pruning cut.
Iowa State University has many resources available to help with pruning all your woody plants.
There is something special about a healthy, well-maintained hedge. A symmetrical wall of green creates visual and physical limits in the landscape and provides a softer effect than wood or plastic materials. Hedges are an effective backdrop for flower beds and borders or may stand on their own in a diversity of shapes and sizes. Shrub plantings can be allowed to grow into a natural, informal hedge or they may be pruned (sheared) into a formal hedge.
Best Shrubs for Formal Hedges
Shrubs suitable for small hedges (less than 5 feet in height) include:
The keys to pruning trees and shrubs are a basic understanding of pruning techniques and knowing when to prune plants. It's also important to have the right tools. There are various types of pruning tools. The best tool for the job is determined by the size of the plant material and the situation.
When buying pruning equipment, select high-quality tools. Good, high-quality tools are not inexpensive. However, if they are used and cared for properly, they will perform better and far outlast the poor-quality, less expensive choices.
Oak trees are valuable assets in the home landscape. Occasionally oak trees need to be pruned for health, safety, and appearance reasons. Pruning oaks makes them more valuable to infection from the fungus that causes oak wilt. By pruning oaks properly, you can reduce that risk and keep trees healthy.
Young or newly-planted trees require special care to ensure their establishment and rapid growth. Young trees must be protected from the careless operation of lawnmowers and weed-trimmers, from vandals, and from harmful construction activities. They also must be given appropriate amounts of water and essential mineral elements (fertilizer) and may benefit from staking, trunk wrapping, and mulching. But pruning may be the most important post-plant maintenance task to perform on young trees if they are to live up to our expectations. The time and expense invested in training a young tree will always be much less than costly and time-consuming corrective pruning of neglected mature trees.
Pruning is a common garden task and proper pruning is important.
Many gardeners have questions regarding the pruning of trees, shrubs, fruits, vines, and other woody plants.
Get answers to your pruning frequently asked questions (FAQs) below.
In spring, many gardeners will be at nurseries, greenhouses, and garden centers looking to buy plants. Selecting the right species and cultivar of a plant for the landscape by matching sun, water, soil, winter hardiness, and other growing requirements is important. Equally important is selecting high-quality plants. Below is advice on how to purchase high-quality plants from the garden center.
Growing trees from seed can be fun. However, the seed of most tree species won't germinate immediately when planted because they are in a dormant state. Dormancy must be broken before the seed can germinate.
Learn about the germination requirements for several specific tree species.
Heavy amounts of snow and ice on the branches of trees and shrubs can cause considerable damage. Improper removal of ice and snow can increase the amount of damage to trees and shrubs. Learn about how to manage ice and heavy snow on trees and shrubs.
An important aspect of pruning is knowing when to prune plants. Proper timing helps to insure attractive, healthy, productive plants. The proper time to prune trees, shrubs, and vines in Iowa is indicated below.
A shrub that flowers in winter? That sounds unlikely but witch hazels do just that - even in Iowa! Witch hazels (Hamamelis) are a group of shrubs that typically have the first (or last depending on what you are growing) blooms of the season in the garden.
During the holiday season, Christmas trees make appearances across Iowa and across the nation as part of the season’s celebration. But there’s plenty to learn about these popular trees. Below is information on the origins of the modern Christmas tree as well as facts and trivia about Christmas tree production.
The Origins of the Christmas Tree
Christmas trees are believed to have originated in Germany in the sixteenth century. There are several legends concerning the origin of the Christmas tree.
Cut Christmas trees are nearly synonymous with the holiday season. Fraser fir, white pine, Douglas fir, and other needled conifer trees are common species used for cut trees in Iowa.
When a cut tree isn’t feasible, rather than resorting to an artificial tree, there are several living Christmas tree alternatives. These not-so-common tree options are sometimes better sized, require less care, or live longer than the standard cut tree. More information about these living alternatives to the classic cut tree can be found below.
Many Americans decorate their home with an artificial, live, or cut tree for the holiday season. Learn more about some simple guidelines that will help ensure an enjoyable and safe holiday season, including where to buy cut trees, types of trees available, how to select, store, and care for the tree, as well as how to best recycle or dispose of it.
The predominate colors of the home landscape in late fall and winter are white and various shades of gray and brown. An excellent way to brighten the drab winter landscape is to plant evergreens (pine, spruce, fir, etc.) and trees and shrubs that possess brightly colored fruit. Growing plants with colorful fruit not only provide interest in the garden during the cold late fall and winter, they can also support wildlife such as birds.
The brightly colored fruit of many of the trees and shrubs will not remain throughout the entire winter. Extreme temperatures in mid-winter will eventually cause many of the fruit to turn brown or black. Hungry birds and squirrels will also devour the fruit. However, the display in late fall and early winter can be spectacular.
Deer, rabbits, mice, voles, and other animals can cause a lot of damage on trees and shrubs over the winter months. Prevention is key to managing these garden pests. By taking steps in the fall, you can prevent damage from occurring over the winter.
Cooler temperatures, crisp breezes, and beautiful fall foliage are some of the many reasons so many people love autumn. The yellows, oranges, reds, and purples seen on many deciduous trees and shrubs in fall come from compounds present in the leaves earlier in the growing season, but masked by the green chlorophyll in the leaves.
Crabapple trees are among the most widely planted ornamental trees in the upper Midwest.
When selecting a crabapple for the home landscape, consider all ornamental features (flowers, fruit display, growth habit, etc.) mature size, and resistance to insect feeding and disease-causing pathogens.
A sampling of some of the best crabapple selections is provided below.
Windbreaks are common sites around Iowa farms and acreages. A well-planned windbreak will moderate hot and cold temperatures, reduce dust and snow, save money in home heating costs, and add monetary value to your property.
Learn about siting, planning, planting, maintaining, and selecting the best tree and shrub species for your windbreak.
Many deciduous shrubs in the home landscape may be propagated by semi-hardwood cuttings.
Trees that can be propagated from semi-hardwood cuttings include willow, maple, tulip poplar, crabapple, and cherry.
Shrubs that can be propagated from semi-hardwood cuttings include rose, flowering quince. forsythia, and dogwood.
Time of Year to Take Semi-Hardwood Cuttings
Semi-hardwood cuttings are taken in mid-July to early fall from the matured current season’s growth. Cutting material should be firm with full-size leaves and has just become woody.
While spring is the traditional planting season in Iowa, late summer and early fall (mid-August to early October) is an excellent time to plant many landscape plants. Below is advice on fall planting of trees, shrubs, perennials, annuals, spring-flowering bulbs, lawns, and vegetables.
Boxwood (Buxus sempervirens) is a dark green evergreen native to southern Europe and northern Africa. It usually grows to a height of three to four feet in Iowa's climate and is popular for borders and hedges because of its dense, dark green foliage. Boxwood requires fertile, well-drained soils and prefers wind protection if grown on an exposed site.
Winter can be tough on boxwoods in Iowa. Over the winter, boxwood may see extensive damage or even die. Sometimes, entire hedges will succumb. Exceptionally low temperatures are to blame in most cases. Boxwoods are marginally hardy in Iowa and can suffer from foliar burn and twig kill in severe winters in exposed locations. Leaves turn brown and twigs die back.
Newly planted trees can eventually add great color and valuable cover to any landscape. But winter’s harsh conditions can hamper, delay or completely derail their development. There are several things you can do to help these new additions to the landscape survive and thrive in colder temperatures.
Water Newly Planted Trees Until the Ground Freezes
The roots of trees continue to grow until the ground freezes in winter. If the weather is dry, continue to water newly planted trees until the soil freezes. Small trees usually require watering for one or two growing seasons. It may be necessary to periodically water large trees for three or four years.