By: Jon Morgenson, Park Horticulturist
Conifers are an important component in our Nebraska landscapes both natural and created. They are a major component of windbreaks and of landscape design for the purposes of screening unsightly views, the framing of desired views and general beautification. Wildlife, including birds and mammals, utilize conifers for food, nesting and shelter. A winter landscape scene in Nebraska featuring snow mantled conifers is a beautiful sight.
Conifers are by simple definition, evergreen, cone bearing trees and shrubs with needle-like or scaly leaves. The family includes many groups (genera) including: pine, spruce, fir, “false hemlock” (Douglas fir), juniper, cypress, hemlock, yew, and a few others. With winter nearly past and spring approaching, I have noticed with increasing frequency dead conifers as well as plants with dead needles and branches. Actually, I began to notice plant death and die back with conifers late last summer and throughout the fall. Conifers are affected by many ‘ills’ and the lists are lengthy, but thankfully many of those ills in the forms of insects and diseases do not attack all conifers. Some are host specific by group (genus) and by individuals (species) within groups. For example, Pine wilt disease affects pine (group) but not spruce, and Pine wilt disease is more commonly found to affect Scotch pine (individual) versus other pines such as White pine; although, over time and with the addition of environmental stress (this past horrific summer) many diseases and insects are increasing their attacks and broadening their host base.
So what is going on? I can’t say for sure but I do have a few thoughts; first and possibly foremost, conifers in their ‘natural’ environments have, like most plants, specific requirements for healthy growth including: temperature, humidity, soil, water and light needs. Many conifers, especially in Nebraska, are found growing in ‘human created’ landscapes where the plants are more often than not from outside our region or from other parts of the world. The soils and environmental conditions where the conifers originate from can be drastically different than where they are being grown in Nebraska. As an example, western Nebraska generally has lighter soils (sandy and rocky), less annual precipitation as well as lower humidity and lower summer night time temperatures. There are six conifer species native to western Nebraska, including: two pine species and four juniper species. Compare this to eastern Nebraska where generally we have heavy soils, greater annual precipitation, high humidity and higher summer night time temperatures. Eastern Red Cedar is the only native conifer in the eastern three quarters of Nebraska and it is found natively growing much farther east and south in the US. Should we be surprised when we consider growing conditions, that our western species can have trouble when grown farther east? Apply this information (growth requirements) to most conifers grown in Nebraska and especially the eastern half of the state.
Conifers (generally) come from ‘uplifted’ or mountainous areas of the world, where they have well drained soils, adequate moisture, lower humidity and cooler summer and winter temperatures (with the exception of southern juniper species and southern pines). Think about spruce and fir in their ‘native’ haunts; we go to the mountains to see and enjoy them and then want to grow them in our yards and in our windbreaks under very different and unfavorable conditions. It is the adaptability and tenacity inherent of the plants themselves that have let them survive under these conditions and that may be changing. I don’t wish to gossip, but I have heard from other plantsmen that it is becoming too hot to grow spruce in western Nebraska. Believe it or not the ‘ills’ may have it and are catching up to our extraneous planting of conifers. Diseases and insects seem to be affecting a greater number of conifer species than in the past, plus we still have some of our old problems (who seem to be increasing their attacks), and some new (to us) problems moving into our area. Have we reached a ‘tipping’ point for the use of conifers in our Nebraska landscapes and windbreaks? I can’t answer that question, but time will tell. I don’t mean to be disheartening. I’m only reporting on my own thoughts and observations. Should we stop planting conifers? No, but we may need to refine our selections and really try to fit the plant to the site where it will be growing. Heat, drought, wind and high humidity all work against (stress) conifers and when combined these factors can become overwhelming. So, what can we do to improve conifer survival?
The saying that “an ounce of prevention is worth a pound of cure” provides us with a base to work from. Here are a few thoughts to follow concerning conifer selection. 1) Select an appropriate plant and planting site. For most conifers a site in full sun with well drained soils is a must. 2) Allow proper plant spacing for air circulation and growth and be prepared to remove or transplant individual trees as they grow if the original plant spacing was close. This will allow for continued good air circulation as the plants mature. 3) Mulch to conserve moisture, control weeds and to provide a cooler root zone environment. 4) Water conifers as needed and especially during times of drought. Conifers are very susceptible to winter desiccation and should go into winter well watered and young plants may need to be watered during the winter when temperatures are warm and the surrounding soil has no snow cover.
I have no doubt that conifers will continue to thrive in our Nebraska landscapes if we select the right plant for the planting site and provide quality after planting care. So what conifers should we plant in the Cornhusker State? I will follow up this article with another, listing some recommended species for spring tree planting projects.
Here are some photos illustrating conifers with problems that I have recently observed in Eastern Nebraska. All photos are of trees found on the campus of Nebraska Game and Parks State Headquarters in Lincoln, Nebraska.