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PLANTING TREES, SHRUBS AND VINES
All too often, schools choose the wrong plant for the wrong site. It is important to understand your site conditions and the potential impacts of human activities on plants in schoolyards to help you plan for their survival. Trees need all the help they can get in the harsh conditions of most schoolyards.
Schools often start by planting trees as a way of building a landscape structure for other grounds greening projects or to create pockets of shade in and around play areas.
The following list will help you avoid the problems that commonly contribute to a low rate of tree survival on school grounds.
First determine what your site conditions are and then plan to improve upon them. You will also need to think about the conditions around your school site.
Thoroughly research your trees and your site conditions and uses. Planting trees in the harsh, hard-surface conditions of school grounds requires careful planning.
Find out which trees and other plants grow well in the vicinity of your school. To help you choose the right plant for your site, walk around the neighbourhood and identify the species that are planted in locations that are similar to the spaces where you plan to plant.
Try to find mature specimens in the neighbourhood of the school so that you can plan for the approximate height and spread of your plants as they mature. This will help you to avoid locating trees and other plants that reach large proportions when mature too close to buildings, overhead wires and cables and underground services such as sewer and water pipes. As trees and large shrubs mature, it will help you to plan for planting in the spaces in between. It will also enable you to plan for planting between and around groupings or rows of small-caliper trees whose crowns are only about six feet across at the time of planting but whose eventual spread may be as much as thirty to forty feet.
Try to find trees that are planted in conditions comparable to your own to help you choose species appropriate to your site. If you plan to plant trees near hard surfaces, study the trees growing along streets and next to driveways in the neighbourhood of your school.
Choose "clean" trees for planting next to play structures. Choose deciduous trees that retain their leaves in Winter such as beeches and trees that have small leaves that tend to dry quickly and blow away such as locusts. Larches, the only deciduous conifer, are also acceptable for planting near play spaces; however, they will not provide as much shade as large deciduous trees. During the Autumn, large leaves can reduce play safety by forming a wet, slippery mat on and around play equipment. Some trees, such as Manitoba maples and large-leaf lindens, can harbour insects which produce sticky substances that can adhere to metal and plastic surfaces of play structures.
Make sure you do not obstruct fire lanes around buildings.
Plan your planting according to the mature height and spread of the tree when planting next to buildings.
It is important to make sure that the plant species you choose are matched to the soil in each location. Some plants are quite particular and will not thrive in some soils, whereas others will tolerate a variety of soil types. Good gardening books provide details on plants' soil requirements including soil density and drainage, and whether the plants prefer acid, alkaline or neutral conditions. Students can perform simple litmus tests to check the acidity of the soil in each planting location. Remember that it is possible to create pockets of varying soils within one planting project. Material can be mixed in with the soil to increase acidity for acid-loving plants and crushed limestone can be added in adjacent spots for plants that need good drainage.
Find out what the soil is like in each proposed planting location. Soils can vary considerably within the same area. Typically, the soil on school grounds is not very good and it has become heavily compacted by foot traffic and grounds maintenance vehicles. Soil that becomes hard and bone dry in the Summer will often turn into a sea of mud in the Spring and when it rains.
Schools with heavier clay soils need to prepare the site carefully prior to planting. Clay soils have low porosity. When a planting hole is dug in clay soil with a spade and without thoroughly breaking up the clay around the hole, the sides of the hole resemble those of a plastic flower pot or bucket sunk into the soil. Rainwater and water from melting snow run into the planting hole and saturate the loosened soil but are not easily absorbed by the surrounding clay. These waterlogged conditions deprive the roots of air and the plant then suffocates or "drowns".
In heavy clay conditions, it helps to first break up the ground to a depth of about two feet in an area at least 8-10 feet in diameter and then to import new soil to form a mound about one foot high. If it is not possible for you to create a mound 8-10 feet in diameter for a single tree, make the planting hole at least twice as wide and twice as deep as the root ball. The soil around and under the planting hole should be loosened up to allow the roots to easily penetrate the soil.
If you have a clay and shale sub-soil, try to dig the planting hole to a depth of two to three feet. The excavated soil can be used to create a berm elsewhere in the yard. This type of site preparation is not normal practice for trees planted in parks or along streets but it helps trees survive in school grounds. The mound of soil can be held in place and defined as a tree space by edging it with seating, low fencing or a variety of materials such as wood and small boulders or stones. When you have prepared the mound, dig the planting hole. After the tree has been planted, apply a layer of mulch such as wood chips to protect the soil and further define the area as a "tree space". The woodchip mulch should be no more than 4" thick. Since woodchips deplete the soil of nitrogen as they decompose, nitrogen-fixing plants such as clovers and vetches can be grown around the tree.
If you have sandy soil, water will drain out of it fairly quickly. Your choice of trees will be limited to species that tolerate dry conditions unless you prepare a large planting hole and mix about two-thirds of new, moisture-retentive soil with the original soil. Peat moss is often recommended as a material to retain moisture in the soil, in particular, for conifers; however, it increases soil acidity and the mining of peat contributes to the destruction of wetlands. In addition to mixing soil that helps to retain moisture in with sandy soil, you can spread a six inch layer of broken up clay soil over the entire planting area. The rain will slowly wash the small particles of clay down through the larger particles of sand. The clay will stick to the surface of the particles of sand and gradually increase the soils ability to retain moisture.
In any type of soil, remember to create planting spaces that are large enough to promote healthy root growth. Trees planted in holes in sidewalks do not grow as well as those planted in a trench that has been capped with bricks, cobbles or gravel to permit greater penetration of water to the roots. Trees' roots have more room to develop in trenches than in small planting holes and therefore trees planted in trenches grow better. Consider digging a trench instead of making several individual holes when planting trees in a row along the edges of non-porous surfaces.
Other planting considerations
When planting deciduous trees near portable classrooms, make sure that the access route is not obstructed should their removal be required. Check with the school board to find out how much clearance is needed.
Avoid planting trees under overhead cables and wires. Trees are often disfigured when branches are cut back to make way for overhead wires and improper trimming may affect tree health.
Trees that thrive in moist conditions such as cedars, willows and red maples are good for helping to solve drainage problems. Areas of the school grounds where excessive puddling occurs can be graded so that rainwater is directed towards plantings of moisture-loving trees. This reduces the size of the wet or puddled areas and concentrates the rainwater where it can be used by trees.
Plant native species wherever possible. Remember that the most suitable plant for a particular site may not be a native species. Some non-native species tolerate hard-surface, dry and salty conditions better than native species. Particularly in urbanized areas, the conditions in no way resemble those of the original natural habitat. The built environment traps heat and temperatures are generally higher than in the surrounding countryside. Many native species of trees are intolerant of urban conditions. Some can survive polluted air, compacted soil, light deprivation and dry conditions and even put up with a certain amount of salt, but the choice of native species that will grow in such stressful conditions is fairly limited
Contact local nurseries and tree growers to try to obtain trees that have been grown locally in the same seed zone or at least in the same growing zone as the one in which they will be planted.
Note: Some agencies only provide funding for native species and you will need to justify the value of non-native species. You may be able to persuade sponsors that planting hardy, urban-tolerant, non-native, non-invasive trees can help to improve the growing conditions for native species planted elsewhere on the site. For example, by forming a windbreak, helping to cool and moisturize the air on the site or blocking salt spray from roads, it can be argued that non-native trees can be used to create healthier conditions for the more-sensitive native trees you wish to plant.
Growing in urbanized areas
Land covered with built structures and non-porous, paved surfaces makes it hard for trees and other plants to grow well. It is important to identify the conditions found in your school grounds so that you can help your plants survive.
Try to find healthy trees and other plants in the neighbourhood around your school that are growing in similar locations to the spaces where you are planning to plant. This will help you choose species that are likely to thrive on your site.
In harsh conditions, it is very important to prepare the planting site carefully. Plants exposed to difficult growing conditions need as much help as possible.
Growing conditions in school grounds are often difficult because:
Planting near hard surfaces
Some important things to remember when planting in heavily compacted soil or near buildings and paved surfaces such as asphalt and concrete:
Shrubs and ground covers that tolerate dry conditions can be planted to form a barrier between newly-planted trees and the edges of areas of hard surfaces such as concrete and asphalt to:
When planning your plantings, it is important to assess the site conditions that may affect the health of trees and other plants.
Trees and other plants growing in school grounds can be affected by:
To help your trees survive, make mounded "tree spaces" or groves of trees rather than planting trees singly and in rows at grade level around the edges of sports and active areas where they tend to sustain damage from children running through them and swinging on their stems and branches.
Children frequently request groves of trees with seating in different shapes set among and around the trees. These areas provide quiet, tree-shaded social spaces away from noise and boisterous play. Creating groves of trees with seating presents an ideal opportunity to educate students on the benefits of deciduous shade trees. Students can directly experience the benefits and understand how their protecting the trees from harm results in the trees protecting them.
It is preferable to plant large-caliper trees because they are less susceptible to damage. Smaller trees require more protection. To help small deciduous trees survive, create a protective barrier between them and children at play and involve the whole school in a planting event. Particularly in Winter, small trees often look like sticks poking out of the snow and children tend to hold onto the stems and swing themselves around them. This usually results in the gradual wearing away of the bark and the eventual death of the tree. Making a protective barrier or creating a special tree space helps to prevent this kind of damage.
Planting near play structures
School board policies often require that flowering trees and other plants that attract bees be placed at some distance from play structures due to bee allergy concerns. Check with your school board to find out at what distance from play equipment flowering trees and shrubs can be planted.
Take care not to plant conifers in places that will obstruct the “line of sight” for school yard monitors or it may become necessary to cut off the lower branches as the trees grow. This often disfigures the tree. If the tree should need trimming to increase visibility, the removal of more than one third of the live branches can result in the death of the tree.
When planting conifers near portable classrooms, make sure that you do not obstruct the access route for their maintenance and possible future removal. Check with the school board to find out how much clearance is needed.
If you are planning to plant conifers close to the edge of a building, try to avoid placing them in front of windows where they can reduce visibility of the yard from inside the building. Also, when planted in front of north-facing windows, the dense foliage of some conifers can substantially reduce the amount of daylight entering the building in Winter. People who feel light-deprived may wish to cut back or remove the tree.
Plant shrubs to:
Plant native shrubs that produce flowers and berries to attract wildlife.
Choose shrubs that will add interest to the landscape throughout the year. For example, plants that retain Autumn leaves until the Spring, evergreens, and plants with colourful stems such as the red-stemmed dogwood.
Plant shrubs with contrasting foliage and different habits of growth to add interest to the plantings of trees and to form a backdrop for perennial gardens.
Watch out for fruit-bearing species such as mulberries whose fruit may drop when ripe and cause pathways to become slippery.
Find out whether your school board requires that flowering shrubs that attract bees be planted at a certain distance from play equipment.
Check the mature size of the shrubs you wish to plant because some can grow to the size of small trees.
Choose shrubs that tolerate dry conditions when planting them as a buffer to protect trees from hot Summer winds.
Choose shrubs such as dogwoods and lilacs whose stems will not break easily and readily sprout again when damaged.
Take care to plant tall shrubs where they will not obstruct sight lines and choose low-growing shrubs for locations where it is necessary to maintain visibility.
Most common house and garden plants such as trees, shrubs and perennials are either all poisonous or have some part that is poisonous. Make sure that the shrubs do not produce poisonous berries that look like fruit we commonly eat. The best way to prevent the ingestion of poisonous plant parts is to teach children not to eat anything growing anywhere before first checking with an adult. At the same time, children can be taught about the wildlife that feeds on plant parts that are poisonous to humans and the use of plants for cosmetics, herbal remedies, and the treatment of diseases, etc.
Try planting shrubs with edible berries that can be harvested in the Autumn and used for class cooking or tie-dye projects.
Some trees such as Scots pine, birches, beech, oaks, yews, etc. can be used for hedging - as long as they are pruned annually. If you are planning to grow a hedge as a windbreak to help improve growing conditions for native species, Chinese elm is a good choice for inner-city schools. This very hardy, non-native tree will need regular pruning if you want to keep it to 3-5 feet in height, but it is an ideal plant for difficult growing conditions. It is fast-growing and tolerates practically any soil type as well as dry conditions, compacted soil, heat, ice, paving and road salt. Its bark and foliage are disease resistant. Also, when the plant is damaged by children playing or vehicles, it soon grows back.
Plant vines to:
Vines are perfect for screening unsightly views, ugly fences and bare walls and tend to be problem-free.
Many schools have built structures on the grounds that could be made more attractive by growing vines on them; for example, the small concrete storage sheds for housing snow blowers, lawn mowers, etc. Trellises can be built for vines and edible climbing plants such as beans, peas, kiwis and cucumbers. Vines improve the aesthetics and do not take up much room at ground level. Make sure that the design of the trellis does not encourage children to use it as a climbing frame. School boards often prohibit the use of pre-fabricated sheets of lattice on trellises since the thin cross pieces are only stapled together and readily fall apart when children try to climb on them.
Fences, storage sheds and walls can also have murals painted on or attached to them before the vines are planted to provide an ever-changing landscape. The vines cover the murals with greenery throughout the warmer months and then when the leaves fall in the Autumn, the murals reappear.
It is important for you to learn about how to care for your plants.
The best way to start caring for your plants even before you have planted them is to generate a sense of ownership among the school community.
Until your trees have become established, or for the first three to four years after transplanting, you will need to have a watering plan in place. This is true for all types of plantings particularly during periods of hot, dry weather. Remember that paving-induced drought conditions already exist, so hard-surface plantings need special attention during dry weather.
The amount of watering will depend on the soil type, plant species, amount of rainfall and type of planting. Porous sandy soils may require watering twice a week during dry spells. If the soil contains a lot of clay, less watering will be needed. When watering trees with a hose, allow the water to soak slowly into the ground for two or three hours at a time. Deep watering helps the roots to grow deeper and provide better support for the tree. If the water flows too quickly from the hose it tends to run off the surface before it can soak into the soil. Creating a shallow water basin around plants helps to hold the water better.
When larger trees are planted, it may be necessary to stake them using two to three stakes per tree until the roots have become established and can support the tree against strong winds. For small trees, place the tree upwind from the prevailing winds.
The stakes should both act as a support and allow for growth. Stakes should permit a certain amount of trunk movement rather than attempting to hold the tree in one position. Apparently, the movement of the trunk by the wind stimulates the root system to develop in a way that anchors the tree so that it can grow to withstand the force of the prevailing winds. Over-staking the tree could retard the formation of the trees' own self-support system. It is important to check the stakes periodically to make sure that they are neither too tight nor too loose. They should be removed after a few growing seasons. Go to Site Design for diagrams on staking.
Mulching around your plants helps to keep down weeds and retain moisture in the soil. Use an organic mulch such as wood chips and straw. Wood chips deplete the soil of nitrogen as they decompose. To help return nitrogen to the soil, nitrogen-fixing plants such as clovers and vetches can be planted (or left in place when weeding) around the trees and shrubs.
Weeding around trees and other plants is important because it eliminates competition for nutrients in the soil. If you have used a wood chip mulch, leave the nitrogen-fixing plants such as vetches and clovers to help return nitrogen to the soil.
Young trees are susceptible to browsing and girdling by rabbits, rodents, deer and other animals. Various kinds of tree-wraps or tree guards are available from garden centres to protect the bark of young trees. Remove the guards in Spring and replace them in the Autumn because tree guards can trap moisture and promote the growth of mold which can damage the bark. The wraps or guards can be left off altogether when the stems of the trees are about 3-4 inch in diameter or when the thin skin of the stem has become thicker and taken on a rough or ridged appearance.
Trees can be fertilized two or three years after transplanting them. Trees suffer from shock when transplanted. If trees are fertilized too soon after being transplanted, tree growth above ground will be promoted at a faster rate than the still-developing or redeveloping root systems can handle. This results in additional stress to the tree. Making sure that the trees are well-watered during the first 3-4 years following transplanting is much more important than fertilizing them.
When planting next to paving which is salted during the Winter, make sure the species chosen are salt tolerant. Also, try to use alternatives to salt that are more environmentally sound.
For plantings near driveways, roads and parking lots, allow plenty of turning space for delivery and maintenance vehicles and school buses to help avoid damage to trees.
Make sure you check on where snow is stored. Snow ploughs can cause considerable mechanical damage to plants by pushing snow and ice into them. By checking on where snow is stored, you can avoid exposing your plants to the chemicals that are present in the snow such as those that come from vehicle exhaust, anti-freeze, oil, grease, windshield fluids, tire particles and salt.