By Andrew Padula, Contributing Columnist and owner of Greer-based Padula's Plants:
When trees are planted in a garden area they provide many benefits like shade for both you and your garden plants, food and shelter for wildlife, added color and texture to your garden, erosion protection, nesting areas for birds, added privacy, and a higher humidity level for your garden. Trees also help improve the soil around the area they are planted in by adding organic material and sometimes nitrogen to the soil.
Trees rarely need an added fertilizer applied to them in order to thrive in their given location as long as their growing conditions are met. (An exception would be a species that has been over-hybridized.) Think of trees as a natural source of slow release fertilizer that is applied constantly to the area they are growing in while the tree is alive and even for a while after the tree is dead.
Because of this constant source of organic material that trees add to the soil in the form of leaves, small branches, dead roots, bark, large fallen limbs, and seeds, adding a tree to your garden helps your garden become more self sustainable naturally.
There is a size and shape of tree for almost every level of privacy that you require. If you are looking for more of a permanent level of privacy, choose dense growing evergreens. If you are looking for some privacy with a view, choose trees that shed their leaves during the winter, or trees that have a loose and open growing habit.
Trees in and around your garden will help to add different levels of light into your garden. This will allow you the chance to grow a wider variety of plants in your garden area, and help keep your garden cooler during the heat of summer.
A large enough tree will also help to create a microclimate in your garden during the cold of Winter.
A tree between 15' - 40' will provide a sheltered area that stays just a little bit warmer then the outside winter air around it. Broad leaf evergreens will help keep your garden the warmest during Winter since they still have leaves which will trap and hold more of the warm air that is trying to escape overnight into space. If the tree is too large, much of the warm air will escape before the lower canopy of the tree has a chance to collect and slow down the air's escape. This extra warmth provided by the tree during cold winter nights here in the Upstate, can provide a location for some Zone 8 perennials. Many Zone 8 perennials thrive here in the Upstate provided they have a sheltered location to live in.
Evergreens with leaves that are not a solid green color are good choices when it come to incorporating trees into a garden design. They offer a wider range of year-round color, adding even more beauty to your garden area. It is even an easier choice for me if they flower as well.
The large roots and feeder roots of trees are excellent in helping to keep soil from washing away during rains. There have been many occasions when I have come across a large steep hill being held in place by one large tree. So, if you have an erosion issue, trees are a good choice. When selecting a tree to help with erosion, choose a tree that has a deep root system and is fast growing. Most evergreens are not good at helping to control erosion because of their slow rate of growth. By the time the evergreen has a large enough of a root system to help control the erosion problem, it may be to late.
Trees will help keep the humidity level in your garden up, which is essential to the health of many garden plants. Hot, dry air is the enemy of plant leaves and helps contribute to a dry and burnt look on a plant's leaves during the Summer and Fall. Trees help to slow down the amount of water evaporating and escaping from the gardens under them.
Trees are essential for attracting wildlife to your garden. A great majority of the wildlife that visits your trees will be different species of birds and insects. Birds are very important for the health of your garden and are at the top of the food chain in many gardens. Birds use the trees to hunt for food in, claim their territory, take shelter from storms, build nests in and raise their young, and to hide from predators. The more species of birds that you attract to your garden, the healthier your garden will be. Mainly because by attracting different species of birds that all make up the top of the garden food chain as a whole, you are helping to break up the top of the garden food chain into more specialized sections. Each species of bird has it's own benefit to offer your garden. And, many times each species of bird has it's own certain kind of insect that it likes to eat. These specialized benefits and micro-sections added to the overall top of the garden food chain, make their way down the food chain and into your garden, increasing the health and beauty of your garden.