Hort Update for November 1, 2022

1. How drought effects plants - beyond wiltingDeath of root hairs, reduced water & nutrient uptake, leaf scorch, reduced photosynthesis

Right now, November 2022, plants are drought stressed, especially trees and shrubs. It is helpful to understand when plants are drought stressed, how drought physiologically affects plants, and how long plants are affected.

A plant is drought stressed when its leaves lose water faster than roots can replace water, resulting in the plant’s water content being reduced enough to interfere with critical plant processes.  

Plant cells are made up of water. When water in plant cells is reduced, they lose turgor and plants wilt. This is an obvious sign of drought stress. Without adequate water, photosynthesis and transpiration are reduced. This produces less obvious stress signs but leads to short and- long term harmful effects.

Transpiration is the movement of water through plants. Water is taken up by roots, moved through plants via the xylem and lost as water vapor through stomates (leaf openings). Transpiration is essential for evaporative cooling of plants so plant tissues do not overheat. Soil nutrients are dissolved in water and distributed through plants via transpiration. Carbon dioxide (CO2) needed for photosynthesis enters plants through stomates during transpiration.

Transpiration is driven by a steady supply of water. When reduced, plant tissues overheat, dry out and often scorch. Fewer nutrients for plant growth are absorbed and distributed. Stomates close to conserve water and less carbon dioxide enters, reducing photosynthesis. As transpiration decreases, respiration increases. In respiration, plants convert photosynthates into energy for growth and other processes. When the rate of respiration exceeds photosynthesis, stored food reserves are reduced.  

Photosynthesis is a plant’s means of manufacturing its own food. It is the process of capturing light energy and converting it to sugar energy. Carbon dioxide and water are key. When reduced by a lack of water and CO2, plants produce fewer photosynthates needed for growth and many other functions such as defense against pest attack. Prolonged drought results in lower food reserves for plants to rely on during other stresses, such as pruning or pest attack.  

Another reason drought affects trees and shrubs over a long period is the loss of root hairs. These are tiny, delicate hairs that extend from feeder roots. They are responsible for the majority of water uptake in the upper 12 inches of soil. When soil is dry, root hairs are lost first and a plants water absorbing capacity is greatly reduced. Even after drought has ended, it may take months or years for plants to repair root systems, extending the stress period. This is often why we see an increase in canker, wilt and other diseases years after a drought, especially in spruce and maple trees.

With the majority of Nebraska experiencing severe to exceptional drought, encourage clients to water trees and shrubs this fall, up until the soil freezes and when soil is dry. Remind them that lawn irrigation is typically not deep enough and that tree roots extend outward 2 to 4 times a trees height. Watering right at or near the trunk of a large tree has little benefit. When watering, the soil is best moistened 10 to 12 inches deep for trees and shrubs. Homeowners can use a screwdriver to help determine watering depth. As a rule, use a soaker hose or hose end sprinkler under low pressure and be sure water is soaking into soil and not running off of the site.

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2. October 28, 2022 growing degree days (GDD)

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3. Perennial garden cleanupOptimize plant health; protect pollinators and other beneficial insects

Fall sanitation or clean-up is beginning to be frowned upon due to pollinator conservation, winter interest and even drought concerns. Alternatively, it is promoted as a management practice in the landscape to help reduce overwintering pathogens and some insects. And some gardeners prefer a tidy winter landscape, thoroughly removing all dead plant material in the fall.

What is the best recommendation for clients? There are good reasons for removing the tops of some plants after they are killed by a fall freeze; but equally good reasons for leaving the tops of some plants until spring. The trend is to leave the tops whenever possible. The ideal situation may be to do a little of both depending on the type of plant and other factors.

Reasons for leaving plant tops until spring:

• Catch snow to increase soil moisture as snow melts. After a dry year or drought, this would be especially important.
• Catch and trap plant debris, like leaves, which act as a mulch to protect plant crowns and roots from winter extremes.
• Provide nesting sites for pollinators. About 30% of native bees nest inside hollow plant stems over winter and emerge the next growing season.
• Provide seeds and protection for some overwintering birds.
• Avoids moisture reaching plant crowns through hollow cut stems which can lead to crown rots or freeze/thaw damage. This is a known problem for Chrysanthemum, Buddleia (butterflybush) and Caryopteris (blue mist spirea).
• Provide winter interest in the landscape such as the tops of ornamental grasses.

Reasons for removing plant tops in fall:

• Reduce overwintering sites for disease pathogens and some insects. Plants that have common disease issues, like peonies, are best cut back each fall. Other plants can be left most years and only cut back if they had a pest issue that season.
• Tidy up the appearance of the garden. For clients preferring a clean garden, opt to cut plants back by leaving at least 8-24 inches of stem to trap snow and leaf debris, and to minimize removal of pollinator nesting sites.
• Lower the fire risk during an open, dry winter if ornamental grasses are planted right next to a building.

Because native bee emergence from hollow stems occurs throughout the growing season, the stems of perennials should not be cut back to the crown in spring. This ensures pollinator nesting sites are not destroyed. Pruning to vary the length of remaining stalks from 8-24 inches will give emerging pollinators a fighting chance to survive. By early summer, emerging new growth will hide the dead stalks.

If plant tops are to be cut back in fall, encourage clients to wait until after a hard freeze. If foliage is green, photosynthesis is taking place and the plant is storing carbohydrates in roots and the crown for next season’s growth. In some instances, there is no ideal situation but to do some pruning in the fall and some in the spring. While there may be mitigating factors, where feasible, the recommendation is to leave the tops in place for winter.

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4. Evergreen winter watering and antitranspirantsContinuing dry conditions increase potential for winter desiccation; watering and anti-transpirant applications can help

Nebraska's dry fall conditions continue, with more areas of the state are advancing to moderate or severe drought. Continue to monitor moisture in turf and landscape plantings. Plants going into winter in drought stressed conditions have increased risk of winter desiccation. 

Use of an anti-transpirant product can also help protect plants, especially broadleaf or conifer evergreens planted in fall under dry conditions. The most commonly available product for home gardeners is Wilt-Pruf®, a natural pine oil polymer that forms a clear, flexible coating on plant leaves and stems. It slows the rate of water loss, but does not interfere with normal plant respiration or photosynthesis. The coating gradually weathers and degrades after application. Use the winter application rate and wait to make the first fall application AFTER plants have hardened off and become dormant, usually late November or early December. Allow at least 3 to 4 hours of drying time, with air temperatures above freezing to make an application. Spray plants thoroughly, covering both upper and lower leaf surfaces to the point of runoff. When the application is complete, clean the sprayer thoroughly according to label directions to prevent product residues from gumming up nozzle tips and other sprayer components.  

Additional anti-transpirant products include Transfilm®and Vapor Gard® (do not use on arborvitae, juniper, cedar). Refer to the label for a full set of restrictions. 

Note: The oil base of anti-transpirant products removes the waxy coating in Colorado Blue Spruce and other blue evergreens, which gives their needles the characteristic blue color, changing plants to green. New growth will emerge with the blue coloration.  

Read and follow all label directions carefully, particularly the re-application recommendations, to avoid plant damage and maintain the product's effectiveness throughout the winter. 

Terminology - The terms anti-desiccant or anti-transpirant are often used interchangeably in relation to these products, which can be confusing. Technically, an anti-desiccant prevents desiccation or drying of plant tissues. An anti-transpirant limits transpiration, a natural plant process in which water is released from natural openings in the leaf surfaces. Just remember, that if transpiration is reduced through the application of an anti-transpirant, winter drying or desiccation is reduced. 

Improving Tree And Shrub Health Through Fall Watering, Nebraska Extension

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5. Fruit tree fall fallow wateringBest practice for home and commercial fruit production

Checking the soil moisture for fruit tree plantings is very important in the fall, going into the winter and the next growing season.  The first 100 days of the spring growing season is critical for branch and bud development for new and established trees; if trees do not have good stores of moisture during this time, overall growth is affected.

In fall, to check for adequate soil moisture levels, shove a long Phillips head screwdriver or a rod with a sharpened point into the ground at least 12 places under the tree canopy and beyond the drip line. Measure how deep each test location can go down into moist soil. If there is little or no moist soil, then slow dripping irrigation can be used on warm days in late fall to help alleviate the lack of moisture in the first 12 inches of soil where water conducting roots will pull and store moisture. Use caution to not over irrigate, which can lead to promotion of weak and tender branch growth.

Next fall, consider planting short term cover crop for the purpose of water fallowing around fruit tree plantings. Water fallowing through growing annual cover crops around fruit tree planting is another option to help moderate soil moisture levels in the fall, winter and early spring. Some cover crop examples that are treated as short term annuals include annual rye, chickpeas, field peas, barely, alfalfa, and wheat. The cover crop reduces weed competition with the fruit trees for nutrients. Organic matter from the cover crop can be incorporated into in the soil the next spring to help improve soil microbial health, soil water drainage, and nutrient holding capacity when the function of the cover crop is finished for the year.

For more information on watering fruit tree, please refer to the  Water Wise Vegetable and Fruit Production NebGuide.

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6. Nuisance home invading insects, spiders and miceExclusion best control

These pests may enter homes in fall as temperatures cool and they begin to look for overwintering sites. Pests like boxelder bugs, millipedes and Asian lady beetles are common. Most are harmless but still a nuisance.

Exclusion is the best means of reducing nuisance pests and mice indoors. Caulk cracks, crevices and conduits of the home. Repair window screens and check that doors are tight fitting. If needed, insecticides can be applied to building foundations according to label direction. Ideally, apply the insecticide from the foundation out to five to 10 feet.

Accidental and Occasional Invaders, Nebraska Extension 
Insects That Overwinter in Your Home, Nebraska Extension
Keeping Occasional Invaders Out, Nebraska Extension
Boxelder Bugs, Nebraska Extension  
Controlling House Mice, Nebraska Extension 
Identification Guide to Common Spiders in Nebraska, Nebraska Extension 
Millipedes, Nebraska Extension
Multi-colored Asian Ladybird Beetles, Nebraska Extension 

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7. Wildlife damage preventionPrevention is best; visit wildlife.unl.edu for additional information

It’s the time of year to prepare for protecting landscape plants from wildlife damage during winter. When green foliage is no longer present, wildlife often turn to other plant parts, such as tree bark and inner wood of young trees. This type of feeding causes damage that is more harmful to plants in the long run.

Managing Deer Damage in Nebraska, Nebraska Extension
Managing Rabbit Damage, Nebraska Extension
Excluding Rabbits, Backyard Farmer
Controlling Vole Damage, Nebraska Extension
Vole Control, Backyard Farmer

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8. The myth of "winter" mulchApplying mulch in early fall does not delay development of winter hardiness

For many years Extension recommended not applying mulch in early fall. The theory originated from the knowledge that mulch moderates large temperature swings in the soil, thus it was predicted early fall mulch applications would keep soil warm longer and delay development of winter hardiness in landscape plants. However, research has shown this theory is not true - mulch does not delay development of winter hardiness. Dr. Linda Chalker-Scott, Washington State University, outlines this and many other properties of landscape mulch in the publication below in which she reviews research from multiple universities over the last 20+ years. 

Impact of Mulches on Landscape Plants and the Environment: A Review, Journal of Environmental Horticulture

Mulch provides several benefits to landscape plants during winter, most notably holding moisture in the soil and moderating soil from extreme temperature swings which could kill roots. But landscape managers do not have to wait until late fall or early winter to refresh landscape mulch. 

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9. Mowing tree leaves into lawnsUp to three inches of leaves can be mowed into turf at one time

While many homeowners bag tree leaves each fall, most professional turf managers mulch mow leaves. Mulch mowing can be easier and returns complex organic matter and nutrients to the soil. Some research suggests mulch mowing can even help control weeds. While this weed control benefit can be sporadic, it can help improve the health of your lawn and soil. Mulching leaves is also easier and less time consuming than bagging. Sometimes a double mowing at a slightly higher cutting height will help shred those leaves and bury them in the lawn. The ground tree leaves won’t add to thatch.  Sometimes tree leaves come fast and quickly pile over the lawn. If you need to rake and bag, compost those leaves and don’t put them on the street or other concrete surfaces. Leaves can leach nutrients that pollute waterways; or be carried to surface water through storm drains where they release nutrients leading to algal problems.

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10. Dormant seedingPrepare site now; seed after Thanksgiving or early March

The best time to seed cool season turfgrass is mid-August into mid-September, but dormant seeding can also be very successful. Dormant seeding is defined as such because seed lies dormant until soil temperatures warm in April or May. Dormant seeding can be done as early as Thanksgiving or as late as March in most locations. The key is to seed after the soil is cold enough that germination will not occur until after soils warm in spring. The benefit of dormant seeding is as soil heaves and cracks during winter, crevices are created for seed to fall into, providing ideal germination conditions in spring. Dormant-seeding may be easier to schedule than spring seeding, because spring rains can make it difficult to seed after March.

There are risks with dormant seeding. It is most effective if weather remains cold enough to delay germination until spring. Occasionally, extended warm periods in winter could allow seed to germinate, and seedlings may then be killed by ensuing cold weather. As with any seeding, soil preparation needs to be done prior to seeding. For dormant seeding, this would be in fall before the soil freezes. If using dormant seeding, monitor the area in mid spring for the need to do additional over-seeding.

Establishing Lawns from Seed, Nebraska Extension Turf iNfo

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.