“To plant trees is to give body and life to one’s dream of a better world.”
The ecological value of trees
If you have already decided to plant a new tree on your property, congratulations! Not only will you be enhancing your garden with a beautiful and ornamental plant, you will also be contributing an ecological benefit to your neighbourhood and the greater community.
When you look at a tree in the landscape, it is easy to appreciate the many useful functions the leaves and trunk provide. The canopy provides both shelter from excessive winds and cooling shade in summer, reducing the effect of a city’s ‘heat island’ while allowing winter sunshine to warm your house. The leaves slow down heavy rains as well as filtering the air, taking in harmful particulate pollutants as well as carbon dioxide and releasing oxygen. Trees provide sap, buds, nuts and fruit that nourish insects and animals as well as being a place where they can shelter.
What is happening below ground is perhaps less obvious but equally important. Root systems prevent soil erosion by holding soil in place and create underground channels that encourage water infiltration. By slowing down the rate of water penetration, tree roots help to prevent excessive rain water from overwhelming stormwater systems and waterways, while filtering out harmful elements. And we are just beginning to understand all the beneficial ways in which the root system interacts with soil microorganisms and mycorrhizal fungi.
Choosing a tree
When selecting a tree, why not choose a native species? The insects and birds will thank you. Native trees and shrubs have coevolved with our local insect, bird and mammal populations and are adapted to our native soils. Our native trees, ranging in size from majestic oaks to the delicate serviceberry are not only beautiful, but also functional. They support the insect life that is needed for both pollination and as a critical source of food for birds. Studies have shown that native trees host a much greater diversity of insects than exotic imported species and that birds will stay in their canopies longer foraging for food. This is important as 96% of North American terrestrial bird species rear their young on insects, mainly caterpillars and moths.
If you have space, consider planting an oak, Toronto’s (un)official tree. Oaks are a keystone species for the food support they offer to birds and insects and are the number one host of caterpillar larvae, a favourite food for raising baby birds. Like all trees, oaks sequester carbon through the process of photosynthesis and are particularly suited to this because of their size, longevity and dense tissues. Oaks are also drought and salt tolerant, making them a good city tree.
When you are shopping for a tree, a small specimen can be a good choice. Not only will it be cheaper, but smaller trees generally have a proportionally larger root system than large trees and will adapt more quickly to their new location, making up the size difference relatively quickly.
In selecting a tree, you will also have to assess the conditions of your site in regards to space and surrounding structures, light conditions, soil type and moisture and drainage. The Landscape Ontario Tree Planting Guide listed below has a handy Soil Assessment Guide on pg. 57, including advice on determining soil texture and conducting a drainage test.
Choosing healthy vigorous specimens that are insect and disease-free and are hardy to your zone will get your plants off to the best start. Plant your tree where it has enough room to grow to its full height and width and where it will not be affected by overhanging wires.
If you can, place your tree in an already existing garden bed or create one for your tree, perhaps underplanted with spring ephemerals and hardy native groundcovers. Many of the insects that occupy trees do not complete their life cycle on the tree. Instead, they fall to the ground and pupate either in the leaf litter beneath the tree or in the soil of a garden bed. Leaf litter left on a garden bed beneath the tree is home to countless beneficial organisms and also contributes valuable nutrients back to the soil as it decomposes.
When to plant
There are two good times to plant in Ontario and both seasons have their advantages. If you plant in early spring, the tree has time to develop a robust root system before the onset of winter. However, supplemental water will be necessary to see your plant through the hot, dry days of summer. If you plant in late summer or fall when the soil is still warm, the plant will be preparing for dormancy and can put all its energy into developing a root system rather than top growth.
Here is what Tree Canada has to say: “Deciduous trees can be planted in the spring, as soon as the frost is out of the ground, or in the fall from leaf-fall until freeze-up. Conifers can be planted early in the spring until four weeks after deciduous trees have opened their leaves, or in the fall, from about the first week of August to the end of October.”
Of course, with containerized plants, you can plant any time during the growing season as long as you take extra care to keep your new plant well watered. Planting in the morning of an overcast day is best.
Preparing the tree for planting
Your new tree will be sold in a container, wrapped in burlap, or arrive bare root. A bare root tree should be planted immediately. If this is not possible, plant it in a pot or heel it in by digging a sloping trench deep enough to hold the roots. Lay the plant on its side, cover the roots with soil and soak with water, being careful not to damage any roots in the process.
Trees in containers, and those wrapped in burlap, can be kept watered and in a shady place until you are ready to plant them. When ready to plant, remove all packaging materials – pots, burlap, twine, tags, etc. Have some wet burlap close by to drape over the roots of the tree once they are exposed. If the growing medium seems loose and likely to fall apart, place the entire root ball in the hole before carefully removing the pot or twine and burlap. With larger specimens, wire baskets may be impossible to remove entirely and have been shown not to impede the growth of the tree. Only the upper portion may need to be cut away before the hole is backfilled.
Checking the root ball
Trees and shrubs that have been kept in containers or balled-in-burlap may fail because their root systems never become established in the landscape. If the tree has been wrapped in burlap too long, the tips of the roots may have grown to the edge of the wrapping, been exposed to air and heat and died. If a tree has been in a container too long, the roots may hit the pot edge and begin to grow in a circle, becoming matted and tangled. Circling roots will become girdling roots and the plant will die from lack of air, water and nutrients.
How can you correct a root ball that has a mass of tangled, circling roots?
If the root ball is small enough, you may be able to gently pull the root ball apart. Loosen and untangle the roots and then pull them apart so they will grow away from the centre. If necessary, cut the roots back to where they curl inwards, using a sharp, clean pruner.
Another option is root pruning, or ‘box cutting’. For a larger plant, either container-grown or ball and burlap, you can cut off the outer layer of circling or damaged roots with a clean sharp knife, stimulating new root growth.
Root washing is a newer and more controversial technique, best done when the plant is dormant. One purpose of root washing is to remove all the foreign potting soil or heavier clay ball and burlap soil to ensure that the bare plant roots have the best possible contact with your garden soil. The other advantage is that you can see any defects in the root system, such as roots growing in circles or growing in the wrong direction, and take steps to correct the root system by removing these before planting.
Preparing the planting hole
Always call before you dig. In Ontario you can contact Ontario One Call, a free service.
The size of the hole should be twice as wide as the current container, or for bare root specimens, wide enough to hold all the roots when fanned out in a circle around the trunk. The hole should only be as deep as the root ball or base of the root. When your hole is finished, it should look like a shallow saucer with sloping sides.
Determining planting depth
The importance of planting a tree at the correct depth cannot be overemphasized. Planting too deeply will eventually lead to the death of the tree. The place where the roots meet the trunk is called the trunk flare or the root collar. Unlike roots, trunks are not meant to be buried in soil and if this happens, they may rot, become diseased or die. The tree must be placed in the ground so that the soil grade is level with the bottom of the root collar. When planted at the proper level you will see the gentle flare of the trunk rise just above the soil line. Err on the side of placing the tree higher above the soil, especially if you suspect the soil will settle or the site is not well drained. It is easier to add soil after planting, than to replant a tree with a sunken trunk flare.
An easy way to see if the tree is placed at the proper depth is to lay the handle of a shovel, or any straight edged stick, across the hole. Kneel down to make sure the bottom of the root collar is level with the bottom of the shovel handle, or stick.
If the tree is bare root, it is easy to see the root collar. However, plants which have been living in a container or arrive wrapped in burlap often have excess soil covering the root collar. This must be removed before planting.
For bare root trees where the roots are not contained in a ball of soil, it is advisable to put a mound of earth in the centre of the planting hole. Place the root collar on top of the mound and let the roots fan out and droop over the sides. Putting the mound of soil in first saves you from the awkwardness of having to fill in under the roots later.
The myth of soil amendments
Past thinking has been to amend the soil before planting, by digging in either inorganic material, such as sand and gravel to ‘loosen a heavy soil’ and ‘improve drainage’ or organic material, such as compost, leaf mold or manure to ‘get your plants off to a good start’. Current thinking does not support either of these approaches.
Inorganic amendments: When you add inorganic materials, such as sand or gravel, you create barriers to the unamended soil, reducing the ability of air and water to move through the soil. This can result in a perched water table.
Organic amendments: It may seem nurturing to add new top soil, manure or compost to enhance the soil, but in fact, you are creating a soil pocket which is unlike the surrounding soil. The roots may initially grow well, but as they come to the edge of the soil in the planting pocket, they will resist growing into the surrounding soil. If amendments are dug into the soil before planting, there is damage to the soil structure and the critical pore space that holds fluctuating amounts of air and water within the soil. As the organic material decomposes over time, soil subsidence can occur, which can contribute to oversaturation of the root ball. You may also be contributing to a nutrient overload by adding more organic material than the plants can absorb.
Any amendments, in the form of compost or leaf mold, should be added to the top of the soil when planting is completed.
Finishing the job
Remove any grass roots, weeds, rocks or other debris from the planting hole.
When the tree is positioned at the right depth, with its roots properly fanned out and the trunk perpendicular to the ground, backfill the hole with unamended soil, using the soil from the planting hole.
Do not be tempted to add additional fertilizer at this point. A high nitrogen fertilizer will encourage vegetative growth at the expense of root growth. Using a high phosphorus fertilizer such as bonemeal or transplant fertilizer can lead to phosphate toxicity and mineral imbalances in the soil. Phosphorus also inhibits the growth of mycorrhizal fungi, undermining the plant’s long-term health.
Use your fingers, or a stick, to gently push the soil around the roots. You want all the roots to have contact with the soil, but you do not want the soil to be compacted around the roots.
Slowly pour a large bucket of water into the hole over the tree roots to reduce large air pockets and settle the soil. You may want to repeat this action, adding more soil, if necessary, until you think that no air pockets remain and the soil is in close contact with the roots. Make any necessary depth adjustments.
Create a small circular bank of soil around the outer limit of the hole. This raised edge will help to contain water over the tree roots. It will also create a physical barrier that will discourage grass from growing into the planting hole and keep the lawnmower away from the trunk.
Apply a coarse mulch such as wood chips or leaf litter at a depth of two to three inches around the tree, keeping the mulch away from the trunk of the tree.
Do not prune the tree, beyond removing any dead, diseased or damaged branches.
Staking the tree
Roots absorb and send water and nutrients to the crown of the tree, but they also anchor the tree in the ground. If the new tree is relatively small with an adequate root ball, it need not be staked. Only stake the tree if the roots will not support its height, if it is tall and exposed to high winds, or it is exposed to rambunctious children. If a tree must be staked, place stakes a low as possible, ideally no higher than 1/3 the height of the tree. Stake the tree loosely so it can move naturally in the wind. This movement will help the tree develop a good trunk taper, increasing its stability. The staking material should not constrict or rub against the bark of your plant. Check periodically to make sure the bark is not being damaged in any way.
Remove staking materials and stakes after roots have established, no longer than one growing season.
Water regularly for the first few years of your tree’s growth, checking to make sure the soil has not dried out. If there is not much rain, gently pour two large buckets of water over the soil once or twice a week or let the hose slowly trickle down the same amount of water. However, don’t overwater. If water is pooling around the tree and the soil is very wet, cut back on your watering and water less frequently.
A sprinkle with the hose for a couple of minutes does more damage than good as this does not provide enough water to penetrate deep into the soil. Newly planted trees must be watered regularly until frost.
Maintain a 2 to 3” mulch layer of leaf litter or wood chips around the base of the tree, a home to countless organisms and a source of valuable nutrients as it decomposes. Mulch forms a barrier which reduces evaporation and traps water, allowing moisture to drain slowly into the soil. It will also suppress weeds and makes their removal easier while protecting the soil structure and moderating swings in soil temperature.
Keep the root zone free of grass and weeds to allow all the nutrients to be directed to your tree.
For root pruning:
Ontario Landscape Tree Planting Guide, https://landscapeontario.com/assets/1570803523.Ontario_Landscape_Tree_Planting_Guide-2019_updated.pdf
For root washing:
Fine gardening, Issue 191 https://www.finegardening.com/article/root-washing-why-and-how-to-wash-roots)
Linda Chalker-Scott. Horticultural techniques for successful plant establishment. https://s3.wp.wsu.edu/uploads/sites/403/2015/03/Planting-fact-sheet.pdf
Linda Chalker-Scott. Information on staking, soil amendments, mulching, etc. https://puyallup.wsu.edu/lcs/
Robert Pavlis, Garden fundamentals https://www.gardenfundamentals.com/planting-trees-right-way/
Toronto Street Tree Guide. https://www.toronto.ca/wp-content/uploads/2021/05/9765-Street-Tree-Brochure.pdf
Native trees available from Leaf: https://www.yourleaf.org/species-offered
Date prepared: February 2022
Prepared by the Toronto Master Gardeners, these Gardening Guides provide introductory information on a variety of gardening topics. Toronto Master Gardeners are part of a large, international volunteer community committed to providing the public with horticultural information, education and inspiration. Our goal is to help Toronto residents use safe, effective, proven and sustainable horticultural practices to create gardens, landscapes and communities that are both vibrant and healthy.
Statement on Invasive Plants: When choosing plants, avoid invasive plants, which can spread quickly and dominate gardens. Invasive plants are sold by nurseries, big box stores or even at community plant sales. Invasives may already be present in your garden. They can invade gardens by spreading from under a neighbour’s fence or may be transported by wildlife. For beautiful, sustainable options to invasive plants, see the Ontario Invasive Plant Council’s “Grow Me Instead – Beautiful Non-Invasive Plants for your Garden” at https://www.ontarioinvasiveplants.ca/resources/grow-me-instead/before purchasing or accepting “gifts” of plants.
Statement on Home Remedies: The Toronto Master Gardeners do not recommend home remedies, as these have not been proven effective through scientific investigation, and may even damage other living organisms in the soil or plants in your garden. There are other garden friendly options you can use.
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