Why are trees so important?

Trees give life to humans and animals alike by producing two of life’s essentials, oxygen and food, and planting trees significantly affects the local ecosystems in which they reside. They provide shelter from harsh winds and their leaves absorb the heat of the city, keeping things cool in summer. Their far reaching roots hold soil in place and fight erosion, and when the leaves fall they provide natural compost.

The relationship between trees and water

Trees and forests play a critical role in capturing rainwater and reducing the risk of natural disasters such as floods and landslides by slowing down the flow of rainwater toward creeks, rivers, lakes, and other water bodies.  Slowing down the flow of water allows it to percolate deep down into the soil to naturally recharge aquifers deep in the Earth. The roots of trees also hold the soil around them in place, preventing sediment from eroding and leaking into nearby waterways.

Dombeya rotundifolia in full bloom at Walter Sisulu National Botanical Gardens. Picture courtesy Random Harvest NurseryBecause trees store and release water vapour through their leaves, they promote healthy rainfall patterns, and when large swaths of forest are lost, areas thousands of miles away can experience drought and other devastating climate effects.

According to the United Nations Food and Agriculture Association, a mature evergreen tree can intercept more than 15 000 litres of water every year.  Their intricate root systems act like filters, and as they absorb water through their roots trees naturally purify the water by filtering out pollutants like nitrates, phosphates, and pesticides, and after periods of heavy rainfall or flash flooding, trees will absorb a significant amount of storm water via their roots, which reduces floodwater damage to ecosystems and infrastructure. Over time, the storm water is released back into the earth and atmosphere via transpiration.

For all the reasons above, trees are vital for the protection of watershed areas of land which drain rain water or snow into one location such as a stream, lake or wetland. Trees are intertwined with watershed health, providing invaluable habitats for many other plant species and wildlife, and are often used as welcome recreational spaces for humans as well.  Watershed ecosystems also supply drinking water for surrounding communities and water for agriculture and manufacturing processes.  

What is climate amelioration?

In urban areas, what is called “climate amelioration” is basically the research and subsequent implementation of changes to our urban spaces in order to improve the land and air quality. The research also includes studying the resilience and adaptation of trees and other plant species to changes in climate. Climate amelioration is now considered to be essential to mitigate the harmful effects already caused by urbanisation, the results of which include flooding and urban heat islands in summer.

City designers and landscapers need to work together to create new integrated green infrastructures and landscapes for our cities and suburbs.  And today the value of trees continues to increase as we realise more and more the value they add to our modern lifestyles and world.  Gardeners play a vital role in climate amelioration by selecting and planting trees that future generations will cherish.

Forest Bushwillow (Combretum kraussii) fruits. Picture courtesy Random Harvest NurseryWhat do I need to consider before purchasing a tree

Trees provide the ‘bones’ or framework of all well-designed gardens, and small trees have become more important in today’s shrinking residential landscapes. Most trees grow more beautiful by the year, providing welcome shade for generations to come, but there’s nothing sadder than seeing a beautiful tree being felled because it was planted in the wrong place, is very messy, has outgrown the site, or poses a problem to the foundations of buildings, water and sewerage pipes etc. Therefore, take time to do some research before purchasing and planting trees, as a hasty decision may lead to a lifetime of regret.

In any garden, but especially in small gardens, a very messy tree, no matter how beautiful can become a bane, so consider this when selecting trees. All plants make a mess, either when the flowers or fruit drops, or when deciduous and evergreen trees drop their leaves, or in the case of tall palms, when their sheaths die off and are difficult to cut off.

There are trees suitable for landscapes large and small, so consider all the factors below carefully before deciding on a tree.  Many small trees grow well in large containers, making them excellent choices for tiny gardens, and if space is extremely limited, consider training a large shrub into a small tree.

Ask yourself “why do I want to plant a tree?”

There are many factors involved in selecting the right tree for your garden, but to start the selection process you need to ask yourself "why do I want a tree?" Is it mainly for shade, or do you need privacy? You may want to design a garden mainly around the needs of your children and pets, or perhaps you just need to add some height, or simply want something pretty to frame a view or to look out on from a window or patio? You may be keen to attract wildlife and only want to plant indigenous trees, or you may prefer to mix indigenous trees with your favourite exotic trees?

Once you know exactly what you want out of your trees, the rest is a bit easier to decide on.

Aesthetics is top of the list when selecting trees

Aesthetics is obviously one on the most important factors for gardeners to consider when planting trees, and because every tree has unique characteristics, they will add to the overall landscape in different ways, and these characteristics will need to be taken into account when planning your garden.

For example, the form or shape of a tree can make or break a landscape, and the beauty of many trees is in their natural shapes, weeping, columnar, conical, or broadly spreading. Evergreens provide shade all year and deciduous trees allow welcome sunshine through in winter and provide wonderful autumn colour, while others are grown for their striking flowers, foliage, bark, or fruits.

Wild Chestnut (Calodendrum capense) Picture courtesy Random Harvest NurseryKnowing the eventual height and spread of your tree is most important

Although aesthetics are very important, the eventual height and spread of your tree at maturity is the most important factor to consider when selecting a tree. Growth rate and the eventual height and spread of plants may vary considerably due to climatic conditions, and especially precipitation, and even a small ornamental tree may, with time, grow much larger than anticipated, or vice-versa. For example, a tree which thrives in warmer subtropical areas with good rainfall may grow very large there, but in hotter and drier regions the same tree may remain a stunted dwarf.

For this reason, it is important to seek advice before making your final decision. Your garden centre or friendly neighbours can help, or you could take a trip to a local botanical garden, or go for a long walk or drive around your neighbourhood and take photographs and notes on how large mature specimens actually grow in your region.

Measure your space before planting trees

In a large garden you may still get away with planting an unsuitable tree, but if space is limited, it becomes imperative that any trees chosen are right for their surroundings in terms of proportion as well as for their decorative value.

Several factors should be considered when selecting suitable trees for your garden. This should be a planned process and you should be able to visualise the end result before you even start planting.

The first thing to do after determining how big your tree will be once mature is to consider the total area available for tree planting. To avoid overcrowding measure your space, draw a plan and divide it appropriately for the new plants. After measuring your space, it is crucial to choose exactly the right placement on your garden plan for the tree, marking it in at its mature height and spread, and ensuring that the tree has ample room both above and below the soil to grow well.

Many trees like the Tree Fuchsia (Halleria lucida) grow well in pots. Picture courtesy Random Harvest NurseryTrees with invasive or non-invasive roots

Knowing whether your tree has invasive or non-invasive roots is another very important factor to consider when selecting trees.  For smaller gardens this is even more important than for larger gardens, and will limit your selection. It is not always easy to find information on the root systems of trees, but your garden centre will certainly be aware of those with aggressive roots.

Take climate into consideration when planting trees

Climate, including temperatures, rainfall and soil type will greatly influence and narrow down your selection, so don’t waste time looking for trees that are not suitable for your growing region.

Why do flowering times vary within the same species?

It’s good to bear in mind that the flowering times given at garden centres and online are only a guide, as plants seem to have a mind of their own, and even if they have been growing in the same garden for years, will often flower weeks sooner or later than expected, depending on prevailing climatic conditions. Flowering times will also often be different if the tree is grown in the summer or winter rainfall regions of the country.

Therefore, it’s always best to check first with your local garden centre for advice as they will know which plants do best in your region, and their flowering times.

Add seasonal interest with trees

When selecting garden trees think about adding seasonal interest, as many trees are absolutely stunning when in full bloom, but once the flowers fade, some may have little interest and may even be untidy. Other trees may not have such spectacular flowers, but they will add year-round interest with their beautiful shape, foliage, or colourful berries.

Umzimbeet (Millettia grandis) Picture courtesy Random Harvest NurseryEvergreen versus Deciduous trees

Although evergreens are most gardeners’ first choice, remember that evergreens generally drop leaves all year round, whilst deciduous trees generally drop their leaves all at once. Deciduous trees can provide spectacular autumn foliage and allow the sunlight through in cold winter regions.

Plant trees to conserve energy and improve efficiency

When a tree is planted in the correct place, it can reduce your home’s cooling and heating costs. Planting an evergreen tree on the northern side of your property can provide a significant amount of shade and natural cooling in summer. And if you plant a deciduous tree in a north facing position it will provide shade through summer while allowing welcome sunlight through during the winter months, helping with heating costs.

When selecting trees consider your neighbours and the view  

Trees that drop messy seed pods or berries are not the best choice near your neighbour’s driveway, or fence, and in townhouse complexes there may be rules governing which trees you are allowed to plant, so make sure you know the rules before designing your garden. Also, if you have a lovely view keep this in mind when planting trees, as they may mature to a size that will obstruct it.  

Consider safety when planting trees

Planting trees too close to your home can cause not only structural damage but also allow easy access to potential pests. To avoid any hazards in the case of a natural disaster, be mindful of safety aspects when planting new trees. Also, bear in mind that plants with sharp spines or thorns may not be suitable for gardens with small children or animals.

Kei Apple (Dovyalis caffra) fruit. Picture courtesy Random Harvest NurseryFast growing trees versus slower growers

For most new gardeners their first concern is normally how fast the tree will grow, but selecting a tree just for its growth rate can be disastrous, and more often than not the tree selected will quickly outgrow the garden and become more of a nightmare than a pleasure. Fast-growing trees generally have soft wood and don’t live as long as slower growers, so consider this if you want to plant trees to provide beauty, shade and shelter for humans and wildlife for many generations to come.

All of the factors discussed above will narrow down your ideal choice in a tree, and although making your final selection may take some time and research, rest assured it will be worth your time and effort. Trees are certainly not cheap anymore and gardeners are spending more time researching and planning their garden before purchasing anything.

On this website you will find a huge selection of exotic and indigenous Trees in my Plant Index and informative articles and plant lists in my Articles Section, so if you are not a member yet support my work and sign up today to have full access.