Vegetation management

This research summary is part of the final deliverable for Report 2025-22, "Comparison of Compost and Proprietary Soil Amendments for Vegetation Establishment," Published in March 2025.

Post-construction roadside soils often suffer from compaction, low fertility, and poor structure, challenging vegetation establishment and stormwater management. This study evaluates the effectiveness of organic amendments (OAs) and proprietary amendments as alternatives to traditional methods. The study involves greenhouse experiments (pot and mesocosm) and field experiments to evaluate vegetation growth and water quality across different amendment and soil applications. Results show that compost amendments significantly improve vegetation growth, with yard-waste compost outperforming others. Biochar shows early growth potential but requires nutrient supplementation for sustained performance. Proprietary amendments support rapid vegetation establishment, enhanced root density, and reduced nutrient leaching, with Sustane 4-6-4 exhibiting consistent growth across application rates. The field study validates greenhouse findings and shows increased biomass and root density with compost amendments, while proprietary amendments result in high nutrient retention and runoff quality. This study highlights the potential use of OAs and PAs to reduce erosion and support long-term vegetation growth. The findings provide practical guidelines, benefits and implementation steps for managing roadside soils after construction activities.

This report fulfills the requirements laid out in Sec. 160.2325 MN Statutes. The goal of the Highways for Habitat Program is to enhance Minnesota roadsides with vegetative buffers and pollinator and other wildlife habitat. This is the first year of this report. More information is available on MnDOT’s Integrated Roadside Vegetation Management webpage.

The Mowing and Vegetation Control Peer Review Team spent five weeks during the summer of 1983 visiting each maintenance area in the state. During these visits questionnaires, sent out ahead of the visits, were discussed with the maintenance personnel as well as inspections made of the current mowing and vegetation control practices in each area. The information gathered by this peer review team has been assembled into this report. This report addresses standards, current practice, equipment, experimental items as well as problems encountered. Included are various figures (charts) which allow comparisons between maintenance areas of the various items under discussion. Finally, as a result of this review, a number of recommendations, that we feel would increase efficiency and productivity, have been included. They include items which may be implemented directly as well as items which may require further study. This report and the recommendations on the following pages have been reviewed by the Maintenance Advisory Committee.

The primary purpose for planting a vegetative cover on roadside areas is to prevent erosion of the soil. A secondary purpose is to create an appealing roadside for the motorist. The intent of this guideline is to reduce mowing to a minimum and yet obtain these objectives.

Minnesota is fortunate to have detailed descriptions of its landscape and vegetation immediately prior to extensive Euro-American settlement. These are contained in the records of the General Land Office’s Public Lands Survey. These records were used to develop an historic vegetation model for Minnesota using statistical modeling. The resultant high-resolution historic vegetation map in GIS format was used as input to the Minnesota Department of Transportation’s (MnDOT) MnModel Phase 4 archaeaological predictive models (Hobbs 2019).

Deicing salt, chiefly sodium chloride, has been identified as an important cause of damage to roadside vegetation. A 1973 investigation along Minnesota roadways attempted to quantify the extent of the damage to roadside vegetation by deicing salt. The 1973 study concluded that there was "no reason to expect widespread increases in salt damage" providing salt usage remained the same. The objectives of this study was to verify these conclusions and to inventory tree growth along Minnesota roads through a re-measurement of the permanent plot system established for this purpose in 1973. The purposes of the re-measurement were: (1) to provide data on species performance; (2) to determine how fast highway trees grow; (3) to ascertain the amount of damage attributable to salt damage; and (4) to determine the likelihood of increased salt damage in the future.

Boulevards are the open space, located just behind the curb, along a roadway. Boulevards serve the essential functions of providing snow storage space for roads and sidewalks, a place for rain and runoff to soak into the ground, and attractive green space in the neighborhoods of our cities. Street trees, or trees planted in the boulevard along a roadway are valuable environmental infrastructure as they save energy and lower temperatures, reduce greenhouse gases, reduce stormwater runoff, and improve aesthetics. Thoughtful planning ensures that the right tree is planted in the right place and with the right maintenance. However, boulevards are often a challenging location to plant trees because of the limited space, utility conflicts, and salt residue from winter maintenance among other factors. This guide will help evaluate the feasibility of the boulevard to support tree planting and suggest tree species with a higher survivability rate for use in the boulevard. Residents and business owners may be concerned about who is responsible for the care and maintenance of trees planted in the boulevard and the cost. City staff and elected officials who support healthy tree lined neighborhoods seek communication resources to convey the many positive attributes of planting diverse tree species. The following best practices are recommended for the successful tree selection for planting in boulevard locations.

The aim of this research is to produce a local, diverse mycorrhizal inoculum for commercial production for use in the Minneapolis/St. Paul area. In earlier studies, spores of several arbuscular mycorrhizal fungal (AMF) species were isolated from a Minnesota remnant prairie and identified by morphological features. For each species, single spore cultures were established and stored in the cold for 6 to 7 years. Objectives of this project were to produce pot cultures from the single spore cultures and to recommend AMF species for commercial production. To check the identity of the fungi before and after inoculum production, genetic identification of fungi used to develop the inoculum should be performed. The extraction and preservation of DNA of AMF species were done. DNA analysis showed general agreement between the morphological and molecular identification of the spores and their placement in genera. However, results suggested that some species placement might not be consistent where these comparisons can be made. Further research may result in the re-naming of some species. Several AMF species are recommended as candidates for commercial inoculum production based on production of spores in pot cultures, on their longevity in cold storage, and in some species on molecular traits.

Information was collected on amounts of deicing salts used and methods of application. Planting practices and investment were also surveyed. Techniques are presented for the recognition of soil-salt and spray-salt damage using visual symptoms and chemical analysis of leaves and soils. Proof was obtained that salt causes much of the twig dieback in hardwoods and needle browning in pines observed along certain Minnesota roadways. The locations are defined where salt-spray and soil-salt damage are likely to be high, moderate, or low. Species are rated for their sensitivity to soil-salts and winter spray-salts. A brief history of salt damage in Minnesota is presented, and the seriousness of current damage is evaluated in terms of mortality, reduced growth and disfigurement, and increased maintenance costs. Seven ways to reduce salt damage are presented including a planting guide to match species to site. Future prospects are estimated for salt damage in Minnesota. A permanent plot system is described that will monitor build up in plant and soil sodium and chloride as well as changes in the vegetation caused by salt damage.