Trees Winnipeg
Education & Publications
Tree Health
DED Management
Setting Down New Roots
What's Bugging My Trees
Spruce Budworm
Setting Down New Roots
A Practical Guide to Pruning
Like us on Facebook
Follow us on Twitter

Tree Care

Tree Health



Far too often, homeowners over-fertilize trees, encouraging rapid, succulent growth. This growth is usually not as winter-hardy as normal growth, and thus more susceptible to winter injury. A another drawback to over-fertilization is that it will cause trees and shrubs to grow too large. Knowing the nutrient requirements of trees can help prevent overfertilizing.

The root system of most trees spreads out over an area one to two times the diameter of the canopy. A tree with branches that spread out 10 feet (3m) on either side of the trunk can have roots extending out 20 feet (6m) on either side of the trunk. The roots near the trunk are the larger anchorage roots, while the smaller feeder roots are located farther away from the trunk. When applying fertilizer to trees, there is no need to fertilize any closer than 2-3 feet. (.75-1 m) to the trunk.

If fertilizing trees and shrubs in a lawn, it is important to get the fertilizer below the level of the grass roots, as grass is a major competitor of nutrients. To do this, make holes about 12 inches (30 cm) deep and 1 inch (.5 cm) wide. These holes should be located under and outside the canopy of the tree. See diagram. The fertilizer should be divided equally amoung the holes. After pouring the dry fertilizer into the holes, fill the holes with soil, and water thoroughly. Fertilizer is concentrated and can burn tree roots. Thorough watering will dilute the fertilizer, and make it available to the tree roots. The number of holes to make is up to the homeowner. The more holes made, the more scattered out the fertilizer will be and the better chance it will be used by the tree.

When fertilizing shrubs, holes can be make into the soil the same way as for trees, or the fertilizer can simply be spread on the soil surface below the shrub. The spread of the root system for shrubs is much the same as for trees, therefore fertilizing outside the canopy of the shrub is desirable. Once the fertilizer is applied, it can be thoroughly watered in, or lightly tilled in and then thoroughly watered in.

There are a number of different fertilizers available to the homeowner. Two factors to look at are the amount of nutrients received for the amount of money paid. Low analysis fertilizers (low numbers) are suitable, but frequently cost more per the amount of nutrients applied. High analysis fertilizers (high numbers) are usually cheaper per amount of fertilizer applied, but can burn more easily if not watered thoroughly. Common tree and shrub fertilizers include 16-20-0 and 10-30-10. These are high analysis fertilizers that will satisfy both the nitrogen and phosphorus requirements of the plants.

For large evergreen and deciduous trees (canopy diameter larger than 15 feet) apply 2 cups of fertilizer per tree covering an area about 100 square feet around the tree. For smaller trees and shrubs, apply 1 cup of fertilizer per tree or shrub.

Fertilizers encourage growth, and therefore all fertilizers should be applied in early spring just before growth occurs. Basically all forms of fertilizer are suitable, although slow release fertilizers may continue to release nutrients well into the summer when it is not recommended. Late summer fertilizing is not recommended as it will encourage succulent growth which will be more prone to winter injury. Fall fertilizing is also not recommended, as leaching of nutrients is possible in both fall and spring.

Recycling and re-using are not new terms for Mother Nature. In autumn, leaves are shed and accumulate on the forest floor. These leaves contain some nutrients. Micro-organisms in the soil, breakdown these leaves, release the nutrients, and the trees and shrubs now pick up the nutrients. In autumn, the leaves are again shed and the cycle continues. In the urban yard, leaves seldom allowed to sit on the soil surface, therefore the nutrients are removed and some fertilizer will have to be added.

Mother Nature also re-uses nutirents. Being that nutrients are not easily obtained in a forest situation, both deciduous and coniferous trees and shrubs remove a great deal of nutrients from the leaves before they are shed in the autumn. The nutrients removed from the leaves is concentrated in the sap and is retained there till next spring, when it is re-used. In fact, about 70% of the nutrient requirement for trees and shrubs is satisified with the re-using of nutrients.



Pruning is an essential part of the DED Management Program. Pruning to remove dead wood helps maintain the health of the tree. A healthy, vigorous elm is less vulnerable to disease or insect infestation. As well, pruning of dead limbs removes beetle breeding material and lessens the risk of the elm contacting DED.

As fresh pruning wounds are attractive to the elm bark beetle, pruning is not allowed during the beetles' active period.

It is an offense under The Dutch Elm Disease Act to prune American elm trees between April 1st and July 31st and Siberian elms between April 1st and June 30th. Elm wood cannot be stored or transported for any reason at any time of the year other than for disposal at an approved landfill site.

Deciduous trees should be pruned while dormant - in late fall or early spring. Exceptions are birch and maple, which must be pruned when the leaves are fully grown or they will bleed. Remove dead, damaged, diseased, weak and thin, or rubbing branches. Remove water sprouts from the trunk and main branches and suckers from the trunk base or roots. Thin the young branches to maintain the desired crown shape and size. Cut just outside the branch collar (the swollen area at the branch base), and do not make flush cuts or leave stubs.

Conifers are pruned to direct new growth, and increase density. Entire branches are not usually removed, since unsightly gaps will result. Spruce and fir must be pruned in late spring after new growth has started but not yet matured. New pine buds should be pinched back in early June when the new growth (candle) has reached full length.

These are general guiding principles for tree planting and care. For more specific information, please see or consult your local garden center or tree care company on proper pruning procedures for individual species.

Tree maintenance also includes watering,fertilizing, insect control and preventative fungicide injections.



Trees constantly lose water to the atmosphere. Water is the single most limiting essential resource for tree survival and growth. Water shortages severely damage young and old trees alike, and set-up healthy trees for other problems. Drought conditions can lead to tree decline, pest problems, and non-recoverable damage. Supplemental watering can greatly assist in maintaining tree health during droughts - both during the growing season or during the dormant season.


Ideally, irrigation should automatically begin when soil moisture reaches some critical measure determined by a moisture probe. Trees should be zoned apart from turf and other landscape plants. Careful tuning of irrigation systems are needed to prevent over-watering trees.

Manually, the best ways to water trees are by soaker hose or trickle (drip) irrigation which you turn on and off. Sprinklers are less efficient for applying water to trees than soaker hoses or drip irrigation, but are easy to use. Even a garden hose, moved often, can provide a good soil soaking. Use a light organic mulch to conserve moisture and apply water over the top of the mulch. Do not concentrate water at the base of the trunk as this can lead to pest problems.

Deep watering a tree with a pipe or wand stuck into the soil 12-24 inches is not as good for trees as surface applications. Most of the tree's absorbing roots are in the top foot of soil. Applying water deeper than this level misses the active roots and allows water to drain away from the roots, wasting efforts and water. Apply water across the soil surface and let it soak into the soil. Surface soaking allows tree roots more chances to absorb any water, helps maintain soil health, and helps maintain essential element cycling and transformations in the soil.


Lay-out water hoses or applicators out to the tree crown edge (drip-line). Try to water the soil areas directly beneath the foliage and shaded by the tree. Do not water beyond the drip-line and do not water closer than 3 feet to the trunk base on established trees. Be sure the water soaks in well. Use mulch and slow application rates on slopes, heavy soils (clays), and compacted soils to assure water is soaking-in and not running-off. If the tree is surrounded with other landscape plants, or by turf, deep soaking water applications will benefit all. Do not spray tree foliage when applying water. Water droplets on tree leaves can lead to pest problems and destruction of leaf tissue through sun damage. Try not to wet the trunk if possible.

Young, newly planted trees need additional watering care. Water does not move sideways in a soil. You must apply water directly over where you need water in a soil. For new trees, concentrate water over the root ball, as well as the planting area, to assure survival.

Old, large trees can be extensively watered over the entire area under their foliage. Another method in watering large trees is to select roughly 1/3 of the area whin the drip-line for concentrated water applications. The whole area below the foliage can be watered occasionally.


The best time to water is at night from 10 pm to 8 am. Trees relieve water deficits (refill) over the night time hours. Watering at night allows effective use of applied water and less evaporative loss, assuring more water moves into the soil and tree. Night time application hours, when dew is already present, does not expand the foliage wetting period for understory plants. This watering cycle minimizes pest problems.

The next best time to water is when foliage is dry and evaporation potential is not at its daily peak. This watering period is late afternoons. Be sure to allow applied water to dry-off of foliage surfaces before the evening dew appears. This dry gap between watering and atmospheric condensation helps minimize pests which require longer wetting periods. This is especially critical where turf surrounds a tree.

Because trees lose water from day to day, month to month, and season to season - dormant season watering during winter drought is important, especially for evergreen trees and juvenile hardwood trees that have not lost their leaves. Because of temperature and relative humidity interactions, much less water is required in the dormant season, but water is still needed. Do not water when the soil surface is less than 40°F.

For every 18°F increase in temperature, the amount of water lost by a tree and the site around it almost doubles. This feature of water loss must be factored into applying supplemental water to a tree. Trees surrounded by pavement and other hot, hard surfaces can be 20-30°F warmer than a tree in a protected, landscaped backyard. Water use rapidly climbs with increasing temperatures, and so should water application volumes.

How Much

Depending upon soil texture, bulk density, daily temperatures, and rainfall amounts, 1-3 inches of water per week should keep a tree healthy. Trees in limited rooting areas, in containers or pots, or on major slopes, need additional care to assure water is reaching the root system in adequate amounts and not suffocating roots from lack of drainage. Five gallons per square yard is about 1 inch of water.

Fine soils (clays) require careful attention to prevent over-watering and root death. Sandy soils can be severely droughty because water runs out of the rooting zone quickly. There are some water holding compounds that are commercially available for keeping water near roots. In addition, composted organic material additions and organic mulch covers on the soil surface can help hold and prevent rapid loss of applied water.

How Often

Trees should be watered once or twice a week in the growing season if there is no rainfall in that particular week. A few heavy (high volume) waterings are much better than many light, shallow waterings. A greater proportion of the applied water is utilized by the tree with heavy watering. Also, light waterings encourage shallow rooting which can lead to more severe drought damage. Once you begin watering you should continue to water until rain comes.

Other Things

Many plants in a small area can effectively compete within the soil to use available water. This water competition can be severe. Remove excess plant competition from around any tree to decrease water stress. Use mulch to conserve water and prevent weed competition.

Xeriscaping, or developing water-efficient landscapes, is becoming more important. There are a number of concepts involved in developing a water-efficient landscapes, when integrated wisely, will conserve water while providing a functional and aesthetically pleasing landscape. Trees are a critical part of any water-efficient landscape.

Donate to Trees Winnipeg
Thank you to Our Supporters
United Rentals

Green Drop
Great West Life
Cambrian Credit Union
The Winnipeg Foundation
University of Winnipeg
Government of Manitoba
The City of Winnipeg
Manitoba Hydro
Starbucks Coffee