Seasonal Tips

Check out this page for articles on seasonal-related tips.

Snowplowing Tips
Iron Chlorosis
Drought Stress and the Landscape
Salt Injury to Landscape Plants
Soil Test, Don't Guess

Snowplowing Tips

When clearing driveways and parking lots of snow, please remember to not push the snow into the roadway and be mindful of stacking of the snow too high, creating dangerous sight restrictions.

If you have fire hydrant located on your property, please ensure that it is easily identifiable in the event of an emergency and not covered by snow.

Please remove parked vehicles from streets to allow snow plows to properly clear roadways.

If your mailbox was damaged due to snowplowing, please contact the Department of Public Works at (248) 735-5640.

Iron Chlorosis

Bright yellow leaves with a network of dark green veins could indicate an iron deficiency (iron chlorosis) in your landscape plants.  For more information, click here.

A tree or shrub in a suburban environment is often a plant under stress. Many suburban trees are growing on sites where roads, sidewalks or other structures restrict root growth. A root system whose growth is restricted is very susceptible to drought stress and flooding stress. Suburban sites that restrict roots usually are prone to drastic changes in the water table. Also, competition for water by lawns can reduce water available to trees and shrubs.

Recognizing Drought - Watering Priorities

Of course, the primary problem with drought is the water shortage, usually from low rainfall. Complicating this situation even further are sprinkler bans and/or voluntary water conservation programs. The establishment of a watering priority management program can minimize drought effects on your landscape plants.

Priority #1: Newly Planted Trees, Shrubs, Lawns
Newly planted trees and shrubs and newly sodded or seeded lawns should receive most of the supplemental water during drought conditions. Because these plants have not had sufficient time to develop deep root systems and adapt to their new surroundings, they depend on surface water for their survival. They can also be quite expensive to replace, so they should receive top priority.

Priority #2: Young Trees and Shrubs
Because young trees and shrubs are not as well established as older trees and shrubs, they will require more water to survive. Typically trees and shrubs planted within the past two years will require irrigation during drought, though not as much as newly planted trees and shrubs. During severe drought conditions, plantings up to five or six years of age may also require supplemental watering.

Priority #3: Flowers, Gardens and Older Plants
Most flower and vegetable gardens will require watering to stay attractive and productive. Mulching will help to retain moisture in the soil around the roots. Most well-established trees and shrubs can withstand a prolonged period without rain or watering. Some established trees and shrubs are more susceptible to drought than others. Birch and dogwood, for instance, tend to be very susceptible to drought and will require more water. Trees and shrubs suffering from other stresses, such as a disease or insect attack, will be more susceptible to drought injury. High value specimen plants may also be targeted for watering.

Priority #4: Lawns
Older, well-established lawns can tolerate long periods of drought by becoming dormant. Dormant lawns can be damaged by foot traffic. During drought conditions, lawns should be watered regularly or allowed to go dormant. Irregular irrigation that causes lawns to repeatedly enter into and recover from dormancy can severely weaken them.

Watering Practices

How you water your plants can drastically affect the efficiency of water usage as well as the ability of plants to survive.

Lawns
During drought, lawns should either be watered regularly (every day or every other day), or be allowed to go dormant. Watering once a week can create a weaken lawn because the plants can repeatedly enter into and break out of dormancy. The best time to water is the early morning. Evening watering leaves turf plants damp most of the night and may allow diseases to attack. However, the benefits of watering can offset the threat of disease attack. Water lawns so that moisture penetrates at least a couple of inches. Hint! Lawns use about 1½ inches of water per week. The best results are obtained by replacing this amount of water through frequent watering. Cans placed in the irrigation zone can be used to measure the amount of water. If there is no significant rain in about three weeks, a dormant lawn should receive a soaking watering. The objective is not to revive the dormant plants, but to re-hydrate the roots and crowns. Without this moisture, the grass plants may not recover from dormancy.

Shrubs
Lawn sprinklers generally should not be used to water shrubs. Contrary to popular belief, wetting the leaves and stems increases the humidity only for several minutes. Wetting the foliage can also encourage disease infection. The best method of watering shrubs is to direct a stream of water near the base of plants until soil is moistened to a depth of 6 to 8 inches. Heavy, infrequent watering of shrubs could promote deeper root development. Directing streams of water at the foliage can dislodge insects such as aphids and spider mites, which tend to build up during drought conditions. Otherwise, it is not advisable to wet plant foliage when irrigating.

Trees
Unless they're allowed to operate for many hours, lawn sprinklers do not water trees. Water small trees by allowing a hose to run near the base until the soil is saturated. Water large trees by allowing the hose to run water at various locations staggered around the drip line (the ends of branches) for several hours. During drought, large trees should require watering only every three to four weeks. As with shrubs, do not wet the foliage of trees except to dislodge large populations of insects.

Caution
Even during drought conditions, recently planted trees and shrubs can be over-watered. If your soil is clay, water can drain slowly from the planting holes. Frequent, soaking watering can flood the developing root zone and damage the developing root system by displacing oxygen with water. Plants that are drowning can develop symptoms similar to drought stressed plants. Hint! You can check the root zone moisture by probing the soil with a metal rod or pipe. This process is similar to checking a baking cake for excessive moisture with a toothpick.

For additional assistance on yard and garden plant care and pest management, call the MSU Extension - Oakland County, Gardening Hotline at 248-858-0902.

Edited by Greg Patchan, Horticulture Agent, MSU Extension - Oakland County, from MSU publications.

Salt Injury to Landscape Plants

Over the past 40 years, amounts of salt used for deicing roadways in winter have increased with greater traffic flow and growing concern for public safety. On heavily traveled highways, 40-80 tons of salt per lane mile per year may be applied. Most people are only too aware of the corrosive effects of salt on automobiles and road surfaces. In addition, salt injures many plants growing along roadsides. The following information describes the nature and symptoms of salt injury to plants and suggests measures to minimize it.

What Is Deicing Salt?

Most deicing salt is unrefined rock salt containing about 98.5% sodium chloride, 1.2% calcium sulfate, 0.1% magnesium chloride, and 0.2% rock. In some cases, a trace (0.02%) of sodium ferro-cyanate may be used as an anticaking agent. Calcium chloride is applied to roads alone or in addition to rock salt when extremely low temperatures are expected. Calcium chloride is 8 times more expensive than rock salt, however, and is used sparingly. Unless otherwise specified, the term salt as used in this bulletin refers to rock salt (sodium chloride). 

How Does Salt Injure Plants?

Salt causes plant injury if it accumulates to excessive amounts in soil near the root system. This frequently happens when salt-laden snow is plowed off of streets and sidewalks and onto adjacent landscapes.

Anyone who has tried to get table salt out of a wet shaker knows that salt readily absorbs water. Rock salt exhibits the same property in the soil, and it absorbs much of the water that would normally be available to roots. Thus, even though soil moisture is plentiful, high amounts of salt can result in a drought-like environment for plants. 

When salt dissolves in water, sodium and chloride ions separate, and the chloride ions are readily absorbed by roots. These ions are carried through the sap stream to actively growing portions such as leaf margins and shoot tips where they accumulate to toxic levels. In leaves, this toxic buildup results in a characteristic marginal scorch. 

Excess sodium in soil decreases plant health and vigor in several ways. High amounts of sodium cause soil to lose its capacity to aggregate into clumps and it easily becomes compacted. Thus, access to water and oxygen is severely restricted, and roots cannot function to their full potential.

Besides restricting the amount of water and oxygen available to plants, excess sodium also obstructs the availability of important nutrients. Most plants only need a small amount of sodium in order to survive. They need considerably larger amounts of magnesium and potassium. All three of these elements use the same chemical route, a shuttle system of sorts, to move from the soil into the plant. Excessive sodium from dissolved salt can tie up the shuttle system and restrict uptake of magnesium and potassium, two chemicals that are essential for making chlorophyll. Potassium deficiencies, in particular, are common in plants suffering from salt injury. 

When salt is deposited on plants by spray from passing cars and trucks, salt may enter plant cells or the spaces between cells directly. One result of salt application by this route is that buds and small twigs of some plant species lose cold hardiness and are more likely to be killed by freezing. 
In addition to the direct effects that salt has on plant growth, affected plants also suffer reduced vigor. They are more susceptible to attack by insect pests and diseases and are more sensitive to other adverse environmental factors such as drought and air pollution.

Symptoms of Salt Injury

Symptoms of excessive salt resemble those caused by drought or root injury. Stunted, yellow foliage, premature autumn leaf coloration, death of leaf margins (scorch), and twig dieback are common. When conifers are injured by winter deposits of salt spray, the affected foliage turns yellow or brown in early spring. If spray is the primary means of salt deposit, discolored needles are soon masked by the new year's growth. However, if salt is also excessive in the soil, the new needles may die as chloride ions accumulate in them. This could be lethal to the entire plant if it happens for several consecutive years. 

One characteristic of salt injury that aids in diagnosis is that it is often confined to branches facing the road. Trees closer to the road suffer more damage than those set farther back.

How Can Salt Damage Be Prevented?

If salt were not used to deice roads in winter, salt damage to plants would be minimal. However, the expense of this solution in terms of human life and safety precludes it. (One might also speculate on the number of roadside plants killed or maimed by errant, skidding vehicles during a snow storm.) Thus, the problem is one of adapting to an undesirable but necessary circumstance.

Calcium chloride is reported to be less toxic than sodium chloride. However, serious problems with the handling and storing of calcium chloride preclude its use by many road maintenance agencies. Foremost among these is that calcium chloride absorbs moisture and cakes even more readily than sodium chloride. It must be kept absolutely dry until use, or it will plug conventional application equipment. Calcium chloride is also much more expensive than sodium chloride -- a limiting factor for many agencies with restricted road-clearing budgets. 

In many cases, sand, light gravel, or cinders provide adequate traction for pedestrian and vehicular traffic. These materials are being used with increasing frequency in place of or in combination with salt to minimize plant injury. 

Late-season salt applications (after March 1 ) are most detrimental to vegetation and should be kept to a minimum. That time of year is when plants are breaking dormancy and their roots are actively absorbing nutrients and water from the soil to provide an adequate supply for the soon-to-follow new leaves. Toxic chloride ions, which are usually leached from soil rapidly, are most likely absorbed at this time.

Avoid piling salt and snow around plants or in places where the resulting salt water will drain into plants when the snow melts. If weather permits, it is a good idea to flush the area around roots exposed to salt with fresh tap or well water as soon as the snow melts. The root zone area on young trees is approximately equal to the area contained within the dripline of the crown. On older trees, it may be twice as large.

Where new trees and shrubs are to be planted and where exposure to salt is likely, select species or cultivars resistant to salt injury (see listing). This list was compiled from a number of sources, and tolerance testing was not uniform. Tolerance varies with many factors, including exposure, soil texture, and plant age. Thus, the list should be used only as a guide. Intolerant species should not be planted within 30 feet of roads or on slopes below roadbeds. Some injury may still occur on moderately tolerant and tolerant species along heavily salted roads. 

Proper planting is important when attempting to establish trees or shrubs along often-salted roads. Newly planted trees are under some stress as a result of the transplanting process itself and are less able to cope with external factors (such as salt) until new roots are established. The well created by settling of new transplants is an excellent place for salty water from melting snow to accumulate. Such wells should be leveled as soon as new transplants become established.

Tolerances of Plants to Deicing Salt

Acer platanoides (Norway maple)
Aesculus hippocastanum (Horse chestnut)
Betula alleghaniensis (Yellow birch)
B. Ienta (Cherry birch)
B. papyrifera (Paper birch)
B. populifolia (Gray birch)
Caragana arborescens (Siberian pea tree)
Elaeagnus angustifolia (Russian olive)
Fraxinus americana (White ash)
Gleditsia triacanthos (Honey locust)
Larix decidua (European larch)
L. Ieptolepis (Japanese larch)
Lonicera tatarica 'Zabelii' (Zabel's honeysuckle)
L. xylosteum (European fly honeysuckle)
Parthenocissus quinquefolia (Virginia creeper)
Picea glauca (White spruce)
P. pungens (Colorado blue spruce)
Pinus mugo (Mugo pine)
P. nigra (Austrian pine)
P. ponderosa (Ponderosa pine)
Populus acuminata
P. alba (White poplar)
P. balsamifera (Balsam poplar)
P. deltoides (Cottonwood)
P. grandidentata (Big tooth aspen)
P. nigraP. nigra 'Italica' (Lombardy poplar)
P. tremuloides (Trembling aspen)
Potentilla fruticosa ' Jackmani i ' (Jackman's potentilla)
Quercus alba (White oak)
Q. macrocarpa (Bur oak)
Q. rubra (Red oak)
Ribes alpinum (Alpine current)
Robinia pseudoacacia (Black locust)
Rosa rugosa (Rugosa rose) 
Salix fragilis
S. viminalis (Common osier)
Shepherdia argentea (Buffaloberry)
Spirea X Vanhouttei (Vanhoutte's spirea)
Symphoricarpus albus var. La evigatus (Garden snowberry)
Tamarix pentandra (Fiuestamen tamarisk) Ulmus glabra (Wych elm)

Moderate Tolerance

Acer ginnala (Amur maple)
A. negudo (Boxelder)
A. saccharinum (Silver maple)
Alnus glutinosa (Black alder)
Fraxinus pennsylvanica (Green ash) 
Juniperus virginiana (Red cedar) 
Pinus sylvestris (Scots pine)
Prunus serotina (Black cherry)
Rhus glabra (Smooth sumac)
Salix alba (White willow)
S. pentandra (Laurel-leaf willow)
Spirea bumalda 'Froebeli' (Froebel's spirea)
Synnga vulgaris (Common lilac) 
Thuia occidentalis (Eastern white cedar)
Ulmus amencana (American elm)

Low Tolerance

Acer rubrum (Red maple)
A. saccharum (Sugar maple) 
Alnus rugosa (Smooth alder)
Abies balsamea (Balsam fir)
Carpinus caroliniana (American hornbeam)
Carya ovata (Shagbark hickory) 
Celtis occidentalis (Hackberry)
Cornus stolonifera (Red Osier dogwood) 
C. stolonifera 'Flaviramea' (Yellow-twig dogwood)
Euonymus alatus (Winged euonymus) 
Juglans nigra (Black walnut)
Ligustrum vu/gare (Common privet)
Malus 'Hopa' (Hopa crabapple) 
Picea abies (Norway spruce)
Pinus resinosa (Red pine)
P. strobus (White pine)
Pseudotsuga menziesii (Douglas fir)
Sambucus racemosa (European red elder)
Tilia americana (American linden)
Tsuga canadensis (Eastern hemlock)
Viburnum trilobum (American highbush cranberry)

Written by: George Hudler, Cornell University, Information Bulletin 169

Prepared and edited by: Greg Patchan, Horticulture Agent, Michigan State University Extension, Oakland County 

Michigan State University Extension is an Affirmative Action, Equal Opportunity Institution. Michigan State University Extension programs and materials are available to all without regard to race, color, national origin, sex, disability, age, or religion. 

Soil Test, Don't Guess

Soil testing is crucial to growing healthy plants and protecting the environment. A soil test will determine the nutrient content of your soil and other conditions and will produce a specific fertilization program for your soil and plants.

From Saturday, March 31 through Sunday, April 15, you can obtain a Michigan State University Soil Test by bringing 2 cups of soil to participating retailers. For a list of participating retailers and additional information about soil testing check www.landscape.org. Each test is $12. A separate test is required for different gardening sites or soil management plans. Each sample should be composed of at least 6 sub-samples taken from normal rooting depth, lawns about 2-4 inches deep, gardens 2-6 inches deep. Do not include roots or other plant material. Mix the sub-sample in a clean pail to obtain the final sample. Samples will be processed by the MSU Lab and the recommendations returned to you by mail through your county MSU Extension office.

For additional information, call the MSU Garden Hotline at 248-858-0902 or MSU Extension, Oakland County, at 248-858-0880.