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Hort Update for March 27, 2019

Hort Update for March 27, 2019, Nebraska Extension,
Serious ConcernsMajor Symptom:
1. Flood damage & recovery Turf, landscape management and recover resources at FLOOD.UNL.EDU
2. Ice encasement - turf May lead to soil oxygen deprivation and root death
3. Crown hydration - turf Loss of winter dormancy and hydration of turf crowns can lead to damage when freezing temperatures return
4. Dormant seeding vs. spring seeding of turf Dormant seeding can take place when soil temperatures are 40 degrees F. or below
5. Wildlife damage - trees & shrubs Damage prevention is best; visit for additional information
6. Delay fruit pruning Recommend clientele prune fruit trees and grapes as late in spring as possible before new growth starts
Minor IssuesMajor points:
7. Snow mold Fungal diseases of turf, seldom warrant chemical control
8. Growing healthy transplants Good growing techniques and tips for clientele trying to grow their own spring transplants
9. Landscape sanitation to prevent water pollution issues Clean up winter accumulations of pet waste and leaves 
Timely TopicsMajor points:
10. Spring preemergent application timing Too early to make applications for crabgrass control
11. Use soil temps to determine vegetable garden planting

View current soil temperature averages at CROPWATCH.UNL.EDU

1. Flood damage & recoveryTURF, Landscape management and recover resources at FLOOD.UNL.EDU

Whether it's a flash flood or a slow onset flood, excessive amounts of water can cause signficant damage. Nebraska Extension is your trusted source for flood-related information. Our campus and county-based experts are ready to help you get the answers you need.



  • Managing Storm and Disaster Damage in Landscapes & NurseriesNorth Carolina State University Extension. Helps professional garden center and nursery staff evaluate the effects of flood damage to nursery stock. 


  • Caring for Flooded Lawns, University of Missouri Extension. Evaluation of damage and management of turfgrass effected by flooding.

Fruits, Vegetables and Food Safety

  • Flooded Vegetable Garden Sites and Food Safety Considerations - Nebraska Extension. The garden season may not have started yet in the heartland, but as the waters recede and clean-up efforts continue, there’s one area of concern that many may not have thought of: the safety of garden produce from flooded areas.


2. Ice encasement- turfMay lead to soil oxygen deprivation and root death

If turfgrass becomes encased with a thick covering of ice for a long period of time (at least 45 days), turf death can occur.  According to Penn State University, as semi-dormant turf under ice continues to respire, oxygen is depleted, and a buildup of toxic gasses such as carbon dioxide occurs. Oxygen depletion and toxic gasses can kill turf when thick ice coverings last for weeks or months during the winter. The most serious damage would likely be on perennial ryegrass and tall fescue.

To determine if a turf area is damaged, take plugs from suspected areas, bring indoors and place in a sunny window or well-lit area under a lamp. Keep the plugs watered and watch for regrowth in about one week. If no regrowth, reseed in spring.


3. Crown hydration - turfLoss of winter dormancy and hydration of turf crowns can lead to damage when freezing temperatures return

Crown hydration is the most common and destructive type of abiotic winter injury and usually occurs in late winter following periods of thawing and freezing, according to Penn State University. During late February and March, temperatures often rise above freezing for a few days at a time. When this happens, some turfgrasses begin to de-acclimate and crowns become hydrated. If a rapid freezing event follows the thaw, ice forms inside the crowns of hydrated turfgrasses and will either rupture cell membranes (when ice forms inside of cells) or draw moisture out of cells (when ice crystals form between cells).

Crown hydration injury is most pronounced on turfgrasses growing in depressions and poorly drained soils. During warming periods in late winter, surface soil temperatures rise, and some thawing takes place. However, the soil remains frozen beneath the surface and water does not drain from depressions. As water from thawed snow and ice collects in depressions, turf residing in these areas becomes super-hydrated. When water refreezes during a rapid and dramatic drop in temperature, these super-hydrated plants are killed.

Winter Kill of Turfgrasses, Penn State Extension


4. Dormant seeding vs. spring seeding of turfDormant seeding can take place when soil temperatures are 40 degrees F. or below

The best time to seed cool season turfgrass is late summer, however spring seeding may be needed. If spring-seeding is necessary, consider seeding before the ground thaws. This is defined as "dormant seeding" because the seed will lie dormant until the soil temperatures warm in April or May.

It is already getting late for dormant seeding. Dormant seeding can be done as early as Thanksgiving and as late as March in most locations. The benefit of dormant seeding is that as soil heaves and cracks during winter, crevices are created providing ideal germination conditions in spring. Additionally, dormant-seeding is easier to schedule than spring seeding, because spring rains make it difficult to seed after March in much of the Great Plains states.

Dormant seeding is more effective when weather remains cold enough to delay germination until spring. Occasionally, extended warm periods in winter could allow for germination and seedling death with ensuing cold weather. Thus a fast-germinating species like perennial ryegrass is rarely used for dormant seeding. If late summer or dormant-seeding are not possible, seed cool-season grasses as early in the spring as possible to take advantage of spring rains and cool temperatures.

Establishing Lawns from Seed, Nebraska Extension


5. Wildlife damage of trees & shrubsDamage prevention is best; visit for additional information

Rabbit, deer and voles commonly damage plants over winter. In most urban home landscapes, the principle culprits are rabbits and voles. On farms and acreages, whitetail deer are also a problem. Economic damage is most common on young trees if they are girdled and killed. Shrubs may die back to the ground but will often regenerate new stems from the base to recover. Vole feeding on lawns will repair itself during spring growth. To prevent a repeat next spring, plants must be protected this coming fall with a physical barrier that will prevent damage.

For information on identifying wildlife damage and exclusion/control methods, go to


6. Delay fruit pruningrecommend clientele prune fruit trees and grapes as late in spring as possible before new growth starts 

The ideal time to prune fruit trees and grapes is late spring, right before they start new growth. Winter damage to fresh cuts is avoided and repair of the cut surfaces is fastest when pruning is done at this time. 

Excessive dormant pruning may cause trees to produce many water sprouts diverting energy from fruit growth and development. Therefore, it is best to limit dormant pruning to cuts those that remove dead, diseased or damaged branches and those the develop the desired tree shape.

Grapevines produce shoots from buds on the previous season’s growth; each shoot will produce the leaves, flower clusters, and tendrils for the current season’s growth. Most healthy mature grapevines will have 300 or more buds that are capable of producing fruit. If all buds are left to grow, the number of fruit clusters would be excessive. Hence, pruning is necessary to create a balanced vine that has neither too heavy a crop nor excessive vegetative growth. A well-pruned vine allows for adequate light interception; good air movement through the vine, which helps minimize disease problems; and facilitates ease of management, including spraying, 

Pruning Fruit Trees, Nebraska Extension
Grape Growing for the Home Landscape, Nebraska Extension


7. Snow moldFungal disease of turf, seldom warrant chemical control

With heavy amounts of snow received in many parts of Nebraska this winter, snow mold damage may be a common sight this spring. Snow molds are fungal diseases active in winter, resulting in nearly circular patches of dead matted turf blades. Damage does not become evident until snow melts in spring.

  • Gray snow mold requires snow cover for infection and patch development. Favored by cool conditions - 32° to 36º F. Mild patch development can occur with 40-60 days of snow cover, moderate damage with 60-90 days, and severe damage with over 90 days of snow cover.  
  • Pink snow mold does not require snow cover and is active under a wider temperature range - 30º to 60º F - so the fungus can be active in late fall and early spring, as well as during winter. 

Snow mold is most likely to develop on tall turf, over 3", that becomes matted under snow after it fell. Continuing to mow lawns in fall, at 2.5 to 3" height, until growth ceases can reduce the potential for snow mold. 

Chemical control of the fungal pathogens is usually not necessary. Rake up matted patches of turf in spring and allow the turf to regrow naturally. A lawn would need to have a history of serious snow mold damage to justify the use of a fungicides.

Gray Snow Mold, Purdue Extension
Pink Snow Mold, Purdue Extension


8. Growing healthy transplantsGood growing techniques and tips for clientele trying to grow their own spring transplants

Some homeowners are interested in growing their own flower or vegetable transplants and need help dealing with common problems. The goal is to produce short, dark green transplants with thick sturdy stems. Below are tips and good growing techniques, along with methods for handling common transplant problems.  

Starting Plants Indoors from Seeds, University of Missouri Extension
Growing Vegetable Transplants, Oklahoma State University 


9. Landscape sanitation to prevent water pollution issuesClean up winter accumulations of pet waste and leaves

When rainwater, often referred to as stormwater, flows over surfaces, it collects what is laying loose in its path, such as grass clippings, soil, or fertilizer and pesticide granules on pavement. This is then carried to surface water. Referred to as runoff or nonpoint source pollution, this is currently the number one cause of pollution of streams, rivers and lakes. To help reduce impaired waterways, do your part by sweeping grass clippings and fertilizer or pesticide granules off pavement; raking and recycling tree leaves; keeping bare areas covered with plants to reduce soil erosion; and cleaning up pet waste which can contribute harmful bacteria to surface waters.

Water Pollution and Our Own Yards, Nebraska Extension


10. Spring preemergent application timingTOO EARLY to make applications for CRABGRASS control

The seed of crabgrass, a summer annual, begins germination when soil temperatures reach 55 degrees F at a two to four inch depth for a few consecutive days. In most years, this typically does not occur until May in Nebraska. The targeted window to apply preemergence herbicides for crabgrass in eastern Nebraska is April 20 to May 5. This year, with continuing cold temperatures and cold soils, delaying application until May will likely be ideal.

Crabgrass Control in Home Lawns, Nebraska Extension Turf iNfo 
Lawn Care Pro Series: Crabgrass and Other Summer Annual Grassy Weeds, Nebraska Extension Turf iNfo


11. Use soil temperatures to determine vegetable garden planting timeView current soil temperature averages at

Many gardeners are anxious to start planting their vegetable gardens, but planting too early is not a good idea. Using specific planting dates, such as planting potatoes on Good Friday, is also not the best practice due to the variable tempertures we experience in any given Nebraska spring. Measuring and planting based on soil temperatures is a better practice.  

To view current soil temperatures, visit Crop Watch

Vegetable Seed Storage and Germination Requirements, Nebraska Extension
Determine Soil Temperatures Before Planting Vegetables for Improved Results, Michigan State University Extension


Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by Nebraska Extension is implied. Use of commercial and trade names does not imply approval or constitute endorsement by Nebraska Extension. Nor does it imply discrimination against other similar products.