Garden doctor
How to keep garden trees in good health
Trees have a huge impact on our gardens and landscapes. These lofty plants bring volume, height, shade, soil stability, wildlife habitats and oodles of oxygen to outdoor spaces. To get the best from both established and newly planted trees, there is much we can do as gardeners. Established trees A mature garden tree is something to be treasured, but they’re not without challenges. Large trees are hungry for light, water and nutrients, meaning they can potentially deprive the rest of the garden of those resources. Light can be addressed with pruning to open up the canopy, irrigation can provide for plants beneath the tree, and nutrients can be added in the form of mulch and balanced organic feeds. Although these giants of the garden may appear all-powerful, they can be easily damaged by our actions. Soil compaction is a common problem around mature trees, preventing air and water getting to the root zone. Surface compaction can be relieved by spiking the soil with a garden fork, but if the problem runs deeper, then specialist companies can be hired in with deep aeration equipment. They will inject pressurised air deep into the soil, opening up fissures and improving the flow of air and water to the roots. And it’s often roots that are most vulnerable to our actions in the garden. Digging or building work can damage trees’ structural or feeding roots. To reduce this problem, avoid any major digging under the canopy of a tree – it has the potential to destabilise the tree and may trigger suckering. Also worth considering are the pests and diseases that can affect trees. Honey fungus is perhaps the most devastating. Once the clusters of buff-coloured mushrooms appear at the base of a tree, it’s game over. Bacterial canker, phytophthora and bracket fungi can be equally devastating and untreatable, but will often take many years to finish off a tree. To identify these diseases and ensure safety, it’s worth calling in a reputable arboriculturalist (consult the Arboricultural Association), who can both assess the tree’s health and recommend remedial treatment. New trees Planting a new tree is an investment for the future, so it’s worth getting it right from the outset. Pick a tree that suits your environment. For example, if your garden is exposed and windy, then mountain species that come from this type of landscape will fare best. Garden trees, especially the smaller ones, are often grafted (growing on the root stock of another tree), usually to control their vigour. Sometimes shoots, or suckers, will sprout from the root stock and need to be pruned off. When planting new trees, the latest advice is to dig a square hole and to backfill it with unenriched soil – this encourages the roots to break out into the surrounding ground more quickly. Young trees should either be staked low down or not staked at all. Watering a new tree is not an exact science, but it’s usually best to water for at least the first two years, giving weekly deep soaks of 20-30 litres or more during the active growing season. Last but not least, avoid planting a new tree on a site previously affected by honey fungus or phytophthora, as these are likely to attack the new tree.
In this regular column, Nick shares his expert knowledge for a thriving garden. NEXT MONTH: Nick advises on how to make the most of clay soil