Last summer the leaves on one of my garden’s young silver birch trees started to go yellow, and then it died. Until then it had always looked healthy. Is there any way to stop this happening to the other birch trees growing nearby, which were all planted at the same time? S Mulcahy, Kerry
Commiserations. It’s always very sad as well as frustrating to lose a much-loved garden tree that you’ve watched grow and flourish over the years. Unfortunately, this happens more than you might think, and the causes can be hard to pin down.
Sometimes, it’s due to a mechanical injury to the trunk or roots of the tree. Much like what skin does for humans, a tree’s bark acts as a protective mantle, regulating temperature, helping to prevent injury and helping to prevent pathogens from entering. It also plays a vital role in transporting water and nutrients, as does the tree’s root system. Injury to either can compromise the tree’s health or even kill it. For this reason, it’s important to regularly check tree stakes, labels and tree ties on young trees to make sure they’re not chafing against the trunk, or that they’re not slowly girdling it. Careless use of strimmers and lawnmowers are other common causes of injury, as is grazing by deer, hares and rabbits.
Trees can also die because of soil compaction caused by the use of heavy machinery nearby, or by heavy materials being stored close beneath the canopy (very often found on building sites), or even by cars being regularly parked or driven over their vulnerable root systems. Birch trees are shallow-rooted, making them especially vulnerable to this kind of damage.
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Another not uncommon cause of death is the developing root system being badly obstructed by buried builders’ rubble. Severe summer droughts and winter flooding can also kill them, which is why it’s so important to both choose and prepare the planting site carefully, avoiding wet ground (unless using a species suitable for this, which silver birch isn’t) and adding annual mulches around the roots in spring. Other common causes of the death of young trees include planting too deeply (birch trees particularly resent this), as well as a tree being pot-bound when planted, which causes its roots to grow in a tight spiral rather than spreading outwards as they should.
For this reason it’s important to dig a wide, square planting hole, using a spade to loosen the soil to a little more than the depth of the tree’s root ball. Always gently tease out the root ball first. Don’t add fertiliser, compost or manure, always plant to the correct depth (the finished soil level should never be above the root collar or nursery line), and only add a stake if the tree is being planted in a very windy, exposed spot, making sure to remove it no more than a year later.
Inevitably, trees can also fall victim to a wide variety of bacterial and fungal diseases, such as honey fungus, bacterial canker and phytophthora, but diagnosis can be difficult (see rhs.co.uk for details). Finally, don’t give up on your birch tree just yet. Trees can sometimes return from the dead, Lazarus-like, if given time.
