CHOOSING THE RIGHT TREES OR SHRUBS

Choosing the right tree or shrub for small garden spaces can be challenging. From the tiny backyards of small inner-city properties to courtyard gardens of villa units, balcony gardens, small public urban gardens, or even smaller areas on larger properties, such as an enclosed courtyard, or a narrow strip between the house and a neighbouring property - the plants that are used in these spaces need to be selected more carefully than for a larger space. Any small place offers unique challenges when you come to select, use, and care for plants. 

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Considerations:

•    Choosing plants without invasive root systems is possibly the most important consideration - those that won’t damage drainage systems, other underground pipes or private and public paving and other hard surfaces. 
•    Size - choosing species that will not grow too tall or present the possibility of falling branches, or encroaching on neighbours, without compromising the need for some shade. 
•    Consider how often the plant will need pruning to contain them within a given space and avoid encroachment on public areas, footpaths, or neighbouring properties. 
•    Urban environments are often heat traps - can the plant chosen cope with these conditions year-round?
•    Watering needs - will the plants you choose need constant watering? In a changing climate, consideration to using more drought resistant plants is a more sustainable approach to landscape design. 
•    Does the planting scheme and the plants you would like to use, fit in with the architectural design of the house and the landscape context of the surrounding landscape?

Problems in Confined Spaces
Although size, and the other considerations listed above, are amongst the first things to consider they are definitely not the only ones, when you choose a plant for a small garden. Some small plants can be a real problem in a confined area, for example:

•    Scent from strongly scented plants will not escape so readily in an enclosed garden.
•    Small areas enclosed by brick or stone walls, or with paving can become heat traps (this can allow plants that might be cold sensitive in your area, to be grown easier; but it can also increase the requirement those plants have for watering).
•    Enclosed spaces are often poorly ventilated; and that can result in greater humidity and lower levels of carbon dioxide than what a more open garden might experience (these things can put stress on the health of some plants).
•    In a smaller area, every square metre gets more intensive use, and that can mean such things as more damage by pets and increased soil compaction from people. 
•    Prickly or poisonous plants are more likely to be brushed in a confined area.
•    Falling leaves, flowers or fruits are more likely to get to places where you do not want them
•    The density of foliage is more likely to impact upon light levels and ventilation.
•    Sometimes the roots of some smaller plants may be more damaging than those of larger plants.

Climate and Plant Growth
Another point that needs thought is that any plant will always grow differently in different places. Most trees and shrubs will grow slower and smaller in colder climates - so often something that might be inappropriate for a small garden in a mild temperate climate, might be acceptable in a cold temperate climate.

Considering Landscape Context

In urban gardens the landscape context is considering the wider ecology of an area, its spatial attributes i.e. the position, area and size of a space and the things within it. This includes how a garden interacts with the local environment and how it fits into the broader area and urban landscape of a village, suburb, or city. Urban landscapes are built environments such as public spaces and include local natural resources - they are formed by the people living within it and their general activities. 

When we choose plants within an already built environment, we need to consider the elements and characteristics that influence the local landscape context for example:

•    How we can connect the garden to other habitats.
•    Land use - we need to look at how land is generally used throughout an area or city. 
•    How the people living with the garden will use that garden. 
•    How the garden will influence or affect the wellbeing of people using the garden. 
•    How we can ensure that the garden will help improve an area and perhaps provide habitat or corridors for local wild-life. 
•    We need to consider the historical context of an area and the gardens and properties within that area - i.e. choosing the trees and shrubs that fit into that general historical context. 

Landscape advantages that we can encourage in the design and implementation of urban gardens include:

FITTING BIG PLANTS INTO SMALL PLACES

Although it is always best to find the right sized tree or shrub to fit a space - some techniques can be used to restrict root systems of larger species. 
Trees that might ordinarily be too big for a small garden may still be able to be grown, using a technique to restrict the plant’s size. The most obvious way is to grow the tree in a tub; or to restrict the spread of roots or foliage by pruning. Many larger plants can be readily kept much smaller in this manner, for example as hedges, or as topiary specimens, or even as bonsai.

Root Control
If you confine roots to a particular soil volume, they can be kept from invading unwanted areas. This technique will also tend to reduce the overall size of the tree. Root control may be effected by any of the following methods:

•    Using root control bags i.e. woven fabrics that restrict movement of roots. 
•    Using root control barriers - rigid plastic or metal barriers placed vertically into the ground to prevent roots spreading outwards from the plant into areas where they might be a problem (e.g. pipes, water features, paved areas). If the barrier reaches deep enough (ideally 60 - 90 cm or more) than any roots that do go beneath the barrier are usually deep enough not to cause problems for paved areas.
•    Use root directors - like root barriers but differ somewhat,  root directors are used to make sure that roots do not enter urban drainage systems, or paving etc. As the name suggests they direct roots away from those areas. They are placed around the root ball which then encourages deeper rather than horizontal roots. It also means the tree will have greater structural support. 
•    Root watering systems that direct water and nutrients to well within the tree canopy either circular (similar to the pliable agricultural pip with slots to allow water release) with the ability to connect to a hose or irrigation pipe; or a horizontally positioned pipe near the root ball at planting. They can release water and nutrients manually or on a timer. This controls roots systems by giving them the moisture they need, rather than spreading out to seek moisture and nutrients.