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Hort Update for March 1, 2022

Hort Update for March 1, 2022, Nebraska Extension,
Winter damage to late summer pruned yew. Growth initiated after late summer pruning was killed by winter conditions.

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Serious ConcernsMajor Symptom
1. Spring pruning of trees and shrubs Tips for shade trees, blooming plants and evergreens
2. Dry, warm winter conditions High potential for turf and woody plant damage by spring
3. March growing degree days (GGD) Lincoln Airport 2/28/22 - 1 GGD,  Understanding Growing Degree Days
Minor Issues
4. Revisiting fall armyworm What to expect in 2022 and is prevention recommended?
Timely Topics
5. Spring lawn care timing Advising customers and do-it-yourselfers
6. What not to plant Nebraska invasive ornamentals
7. Goji berry Latest fruit craze is a potential problem plant
8. Fruit tree pruning Common client questions and answers
9. Don't move firewood Make clients aware of the dangers related to moving firewood

1. Spring pruning of trees & shrubsTips for shade trees, blooming plants and evergreens

March is a fine time to prune most trees and shrubs - but not all. By waiting until just before new growth begins, pruning wounds are sealed more quickly and there is a reduced risk of cold temperature injury.

Spring & Summer Blooming Shrubs
Some exceptions to March pruning are spring flowering shrubs like lilac, mockorange, Forsythia, Weigela and some Hydrangeas and Spirea. These are best pruned just after they finish blooming. Spring blooming shrubs bloom on previous year’s wood. Pruning during winter or early spring removes blooming wood and will reduce or prevent blooming this season.

Summer blooming shrubs like Potentilla, rose of Sharon, St. Johnswort and some types of Spirea and Hydrangea, can be pruned when dormant. These shrubs bloom on new wood that grows each spring.

Some plants create confusion because they bloom on new or old wood depending on the species or cultivar. Hydrangea, Spirea and Clematis are examples. When buying plants, the tag or related information will state blooms on new wood or blooms on previous years wood.

If a plant blooms on new wood, it can be pruned in late winter while dormant. If it blooms on previous year’s wood, pruning at this time of year will reduce flowering. It will not harm the plant, just reduce or prevent blooming.

Pruning Shade Trees
When it comes to shade trees, March is a good time to prune. The later in March, closer to the start of new growth that a tree is pruned, the better.

You may have heard there is a time when oak trees should not be pruned. This is due to the disease oak wilt. The fungus causing oak wilt can be spread by beetles attracted to sap oozing from tree wounds. While oak wilt has only been found in far eastern Nebraska, it is recommended to avoid pruning oak trees from April through June, making March a good time to prune. In this case, the earlier in March is better. The same is true of plants infected with fire blight or other canker type diseases.

Evergreen Trees & Shrubs
As for landscape evergreen trees, it would be best if they were not pruned. Unless a tree is grown to sell as a Christmas tree, evergreens maintain a more natural shape if not pruned. With frequent shearing, the client ends up with a tree that is bare in the center with only an outer shell of green needles.

The only pruning that may be needed for evergreen trees is the removal of a double leader on young trees to avoid structural issues as the tree grows larger. The sooner double leaders are removed on any tree, the better.

For evergreen shrubs like Juniper or Yew, where size may need to be controlled or a client prefers a sheared form over a natural form, these can be pruned anytime except during very cold weather. Late winter, just before new growth begins is a good time to start. Be sure to stop around mid-August.

When pruning any evergreen, do not prune beyond the green needles on a branch. Most evergreens lose inner needles and will not generate new growth from bare wood. Once an evergreen is pruned too far back, new growth will not occur to cover bare areas.


2. Dry, warm winter conditionsHigh potential for turf and woody plant damage by spring

Drought Map, February 22, 2022Winter drought conditions are worsening across the state.   

Injury to turfgrass can occur. Desiccation injury is usually greatest on exposed or elevated areas where surface water runoff is great. It is also prevalent on poorly rooted turf that cannot take-up water from deeper in the soil profile. Winter watering is underway on most golf courses where it is feasible and professionals will need to continue monitoring turfgrass sites for dry conditions.

If winter irrigation is used, only water when the soil is not frozen and air temperatures are above 40 degrees F. Lightly irrigate high value turf on dry sunny days when the air temperature is well above freezing where feasible.  The goal is to rehydrate plant crowns (and lower leaves) back to a survivable level and restore soil moisture at the surface.  Avoid excessive quantities of water which may fill soil pores or runoff and present an icing hazard when cold temperatures return.  Also avoid trafficking high value turf areas as winter drought, like summer drought, increases the risk of traffic injury.  To prevent crown hydration injury, avoid watering before a sudden temperature drop is forecast, when the ground is frozen, or in low areas where water might collect and stand due to frozen soil or poor drainage.

Fighting Dessication: Should we water turf in winter?, Nebraska Extension

Trees & Shrubs
Winter dessication injury is often most severe on evergreens and broadleaf evergreens. Damage occurs when the amount of moisture lost through foliage is greater than can be replaced by roots from dry soil. Plant tissue dries out resulting in browning of foliage and dieback, which is often not seen until spring. Injury is found on the outer portion of the branches and is most severe on the side of the tree facing the wind or a source of radiated heat, such as a south or west-facing brick wall or street.

Watering mid-winter is recommended if soils are not frozen and air temperatures are above 40º F. 

When spring arrives, it will be important to remind homeowners not to be in a hurry to prune damaged tissue. While green needles may be brown, the buds on the branches may still be viable and will eventually open. If damage is not too severe and twigs are not killed, the area may eventually fill in. With evergreens, pruning cannot be done past where there is green leaf tissue. If this is necessary, consider replacing the plant with one better adapted to the site.

Green and Growing Tip: Broadleaf Evergreens, Backyard Farmer


4. Fall armywormWhat to expect in 2022 and is prevention recommended?

2021 was a very unusual year, in that Nebraska experienced one of the sporadic outbreaks of fall armyworm damage in late summer. So what should professionals expect for summer 2022? Is there any benefit to preventive insecticide applications? 

Fall armyworms are present every year, but usually in such low numbers later in the summer they don't cause any significant level of damage. The insects do not overwinter in Nebraska - this tropical species overwinters in the extreme southern tips of Texas and Florida. So even though this was a warmer than normal winter for Nebraska, we still had enough cold periods to kill off any fall armyworms. 

But the adult moths are good flyers and are either blown north on storm fronts or migrate north every summer. Spring and early summer storm activity - with storms blowing up out of the south - may be the best predictor of when fall armyworms will arrive in Nebraska. Watch for the adult moths, which are similar to cutworm moths, having dark gray forewings mottled with lighter and darker patches. Their wingspan is about 1.5 inches and they have a whitish patch near the wing tip. Adults can be found feeding on flower nectar. Also watch for egg masses, usually several hundred eggs laid together on flat surfaces like tree leaves, light-colored fence posts, fence rails, garden furniture, etc. Egg masses are light gray and fuzzy. 

The likelihood of another outbreak this year is low, early season preventive insectides are not recommended.  

More information on moth identification and control.
Fall Armyworms 2021, Nebraska Extension


5. Lawn spring care timingAdvising customers and do-it-yourselfers

For do-it-yourselfers, lawn care should not begin until after the grass breaks dormancy and begins to grow and soils have warmed. Mowing is not needed until after the grass begins to grow and requires mowing. Then maintain the same height of 3 to 3.5 inches from the first to the last mowing of the season.

Preemergence herbicides targeted at controlling crabgrass and other warm season annual weeds should not be applied until soil temperatures reach 50 degrees Fahrenheit. Soil temperatures across the state can be found at: CropWatch - Soil Temperature Update. 

Fertilization should not begin until soil temperatures are even warmer, ideally sometime in May. A well-timed fertilizer application supplies the turf with nutrients when they are needed by the plant and when the soil isn’t already supplying the nutrient. See Cool Season Lawn Calendar - Eastern Nebraska.


6. What not to plantNebraska invasive ornamentals

It's important for professionals to be aware of noxious or invasive plant species that homeowners should not be planting. The Nebraska Invasive Species Program is a great resource for in-depth information on the plants below and for all the latest news on Nebraska Invasive Species. 

State Noxious (Formerly Ornamental) Weeds - Legally designated by the Nebraska Department of Agriculture as harmful or destructive, posing a serious economic, social or aesthetic threat. Control can be enforced. 

Priority Invasive Weeds - These species are top priority for eradication of new and established populations. 

Established Invasive Plants - Prevention of spread to new areas is a priority. 


7. Goji berryLatest fruit craze is a potential problem plant

Goji berry, Lycium barbatum or L. chinese,  is a non-native fruit plant commonly found in garden catalogues in recent years. This perennial shrub has weak, slightly spiny branches which tend to sprawl in the garden and have low production. Unfortunately they sucker easily from the roots, which is often not a desirable feature for gardeners. Plants are hardy to USDA Zones 2-7, so seeds may also germinate in the garden, making this plant a pest. Buyers (and gardeners) should beware this potential garden thug. 

Goji Berry Culture, PennState Extension


8. Fruit tree pruningCommon client questions & answers

Many gardeners have questions about spring pruning. Specifically, is the time to prune affected by this year's warm winter conditions? Here are a few pruning -related questions you may be receiving from clientele right now.

  • Will early pruning cause fruit tree leaf and flower buds to develop earlier and possibly be damaged by normal spring frosts?
  • Should pruning still be done in March and early April or should it be done earlier since conditions have been so warm?
  • Does pruning too late – after warmth has caused buds to swell or flowers to bloom – have detrimental effects on fruit production in the home orchard?
  • What about shade trees? Should any adjustments in the time of pruning be made in response to recent warm conditions?

Let’s discuss each question, but first it’s important to understand woody plant leaf and flower buds were formed last fall. They are already present on branch twigs, so you should be able to find dormant buds when doing a close examination of your plant now. The presence of buds now is normal and does not mean plants are actively growing yet.

<p?Does pruning cause early leaf and flower bud development?No, pruning actually has a slight delaying effect on bud growth. After pruning, a plant has to adjust and begin sending growth hormones to new buds, since the preferred buds at the tips of branches removed are now gone. This process could take about 10 days, so bud development is slowed down a little. But it’s risky for growers to use pruning to slow down and "protect" flower buds.

Best time to pruneLess winter hardy tree fruits like peach, apricot and sweet cherry should always be pruned in late winter, usually mid-March to early April, no matter how much warm mid-winter weather we experience. Pruning is done just before new growth starts. This is also the best practice for the more cold-hardy fruits, like pear, apple, plum tart cherry and shade trees.

Why? Pruning at this time has two big benefits. First, there is less chance of cold damage at the pruning sites. Second, plants heal pruning wounds much faster if the cuts are made just before new growth begins.

There still plenty of time for cold late winter temperatures and freezes, which will slow bud development down. And early pruning leaves plant susceptible to cold temperature injury at the pruning sites.

Does late pruning, after blooming or growth has begun, have a detrimental effect on fruit trees?
Pruning can be done after growth begins, but it becomes very important to prevent the spread of common diseases, like fireblight and brown rot, with each cut of your pruners. That’s one of the main reasons dormant pruning is preferred.

Pruning after blooming begins does not reduce fruit production more than normal dormant pruning. Some flower buds are removed, but fruit trees do require annual thinning of fruits. In particular, peaches normally set many more fruits than the tree can support physically or develop to a good size. Breaking of peach tree branches under excess fruit weight is a common occurrence. Only 10% of peach flowers are needed for full crop set.

Fireblight is a serious disease of apple, cherry, crabapple, pear and plum. Watch for brown dying flowers and twigs dying back quickly with brown or black leaves. Prune out and discard all infected twigs and branches with cankers. Cuts should be at least one foot below the infected area. Pruning tools should be disinfected after each cut by dipping the cutting surface into a disinfectant such as 70 percent alcohol or a diluted household bleach solution (one cup household bleach to nine cups water).

Brown rot is a common disease of peach and apricot which results in stem cankers. Watch for signs of cankers during pruning. Cutting into an active canker could result in spreading the disease to new stems. Remove cankered stems by cutting back several inches into healthy tissue. As with fireblight, cleaning pruners between each cut is the most aggressive way to prevent spreading the disease throughout trees.

What about shade trees?
For homeowners who can choose the ideal time to prune, shade trees should also be pruned just before growth begins in spring. If you need to hire an arborist to prune a large tree, then anytime between now and early May would be a great time to prune.

<pMore information
Pruning Fruit Trees, Nebraska Extension 
Tree Pruning, Nebraska Forest Service


9. Don't move firewoodMake clients aware of the dangers related to moving firewood

EAB MapThe Nebraska Department of Agriculture (NDA) strongly advises that in general, no firewood be brought into Nebraska from other states to prevent the spread of pests. Arborists taking down trees for clients should make them aware of the dangers of moving firewood. They should use firewood at home and not take it camping with them. 

Nebraska rescinded the state quarantine related to emerald ash borer on October 29, 2020 and the USDA federal quarantine was rescinded on January 14, 2021. However, other states still maintain state quarantines and firewood restrictions. Arborists should contact NDA prior to moving firewood to another state to determine certification requirements. 

Entry of walnut wood into Nebraska is still restricted to prevent the introduction of thousand cankers disease. Other states also have quarantines in  place to prevent the further spread of tree pests like sudden oak death, gypsy moth and Asian longhorned beetle which makes it illegal to bring firewood into Nebraska from most out-of-state sources.

Don't Move Firewood


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.