Salt Damage on Trees

Winter 2010 lingers on across Tennessee, Virginia and North Carolina. The white coating of de-icing salts over streets and highways can damage many trees and shrubs. Salt spray and salt deposits may also leach into the soil and become equally damaging. Plant species vary in their sensitivity to salt injury.
Browning of the tips of needle and broadleaf evergreens is a typical symptom of salt injury. Needle loss can be an extreme result, with evergreen branches becoming progressively bare. Often, evergreens become so weakened and stressed that new spring growth does not slow the needle/leaf loss. Overall tree health gradually declines.

The following practices can minimize salt injury to trees and shrubs:
1. Applications of water will leach some salt out of the root zone. Plentiful spring rainfall will help in this leaching/cleansing process. As much as 6 inches of water is needed to leach about half the soluble salts. In addition, applying gypsum (calcium sulfate) displaces the sodium in the soil.
2. Plant trees in salt-prone areas that are less vulnerable to salt damage. All trees are affected by salt to some degree, but some species are more tolerant than others. A listing of the susceptible and resistant trees to salt (University of Tennessee Extension publication SP-610) appears below.
3. In future plantings, avoid setting salt susceptible tree species in areas where salt-laden brine and slush are likely to accumulate.
4. Plants that are injured and exhibit dieback should be watered, pruned and fertilized.
Fresh mulch may be applied to help reduce water loss during the normally dry summer ahead. Weakened or stressed trees are also more susceptible to disease and insect pests.

Table 1. Salt Susceptibility of Trees
Vulnerable to Salt
Red Maple - Acer rubrum
Sugar Maple - Acer saccharum
Mimosa - Albizia julibrissin
Serviceberry - Amelanchier spp.
American Hornbeam - Carpinus caroliniana
Dogwood - Cornus florida
Hawthorn - Crataegus spp.
American Beech - Fagus grandifolia
Yellow Poplar - Liriodendron tulipifera
Crapemyrtle - Lagerstroemia spp.
Magnolia - Magnolia grandiflora
Spruces (most) - Picea spp.
Eastern White Pine - Pinus strobus
Scotch pine - Pinus sylvestris
Lindens - Tilia spp.
Eastern Hemlock - Tsuga canadensis

More Tolerant to Salt
Norway Maple - Acer platanoides
Buckeyes - Aesculus spp.
Birch - Betula spp.
Hickories - Carya spp.
Ash - Fraxinus spp.
Ginkgo- Ginkgo biloba
Honeylocust - Gleditsia triacanthos
Black Walnut - Juglans nigra
Eastern Redcedar - Juniperus virginiana
Cottonwood/Aspens - Populus spp.
Cherries - Prunus spp.
Oaks (most) - Quercus spp.
Black Locust - Robinia pseudoacacia
Yews - Taxus spp.
Elms - Ulmus spp.

Why My Tree Or Shrub Doesn't Bloom

Frustrated by a fruit tree or ornamental tree that does not bloom? There are 5 primary causes:

1. Lack of sunlight - insufficient light reduces flower bud development
2. Fertility - too much nitrogen fed to plants can over-stimulate vegetative growth, either delaying or preventing flower bud development
3. Winter injury or chilling tender flower buds in one or more spring frost
4. Pruning at the wrong time of year, essentially removing all flowering wood
5. Alternative (biennial) flowering when a plant bears too much fruit and will not initiate new flower bud for the next year

All these factors are inter-related. While bad pruning practices may reduce flower bud numbers, good timely pruning practices increase blooming. Usually, an unpruned tree or shrub does not bloom heavily. A shrub or tree with an open branch canopy in full sun will flower reliably every year.

Prune spring flowering shrubs and trees immediately after flowering. These plants set flower buds on woody growth produced in the summer. Summer-flowering plants set their flower buds on spring wood in the same year when they bloom. They can be pruned in late summer or wait until late winter and early spring.

Root Injury to Container Plants

The 4 most common reasons why gardeners lose outdoor container plants during the winters are:
1. Sub-freezing temps
2. Soil freezing for long periods
3. Waterlogged roots
4. Dessication from dry winter winds

Roots are not as cold hardy as above-ground shoots, trunks, branches, etc. Evergreen plants become more challenged when the soil media is frozen. Their leaves demand more water and nutrients that the roots are not able to supply from the frozen ground.

Root injury for most woody tree species begins at 22°F. This is soil that has little water in it. Keep in mind that water freezes at 32°F. So, one tip is to keep container plants watered, but not waterlogged. Most plants are injured when soil temps hit 16°F over a 24-hour period.

Pots must provide adequate drainage. Planting in a soil-less media containing high percentages of an organic component such as peat moss and/or compost, plus a gritty substance as coarse sand, tiny pea gravel or perlite for aeration and drainage. The pot should include bottom holes to weep out excess moisture.

Evergreens naturally shed most rain and snow like an umbrella and supplemental watering is critical for these plant compared to deciduous plants. Irrigate containers at least twice monthly, assuming that natural rain and snowfall will supply the rest.