I have another pest to add to the growing list of threats to a box plant’s health and well-being. This one is the red ant (Myrmica rubra).
At a place where I work there had been a lot of head scratching trying to discover the reason why the leaves of single box plants were starting to yellow in a healthy, established box hedge. If it was nutrient deficiency or lack of watering then you would expect to see other box plants in the hedge displaying the same symptoms.
The answer was explained by small mounds of loose, fine textured soil around the base of the box- the spoil heaps from red ant excavations as they build their nests.
Red ants don’t directly damage the box plant. Their activities disturb the soil around the base of the box, creating small air pockets that can cause the roots to dry out. The dried out root system doesn’t access the necessary nutrients and water required for healthy growth and the leaves begin to yellow. The box plant will eventually die if left untreated.
This soil disruption activity by the ants can be beneficial to some plants with deep root systems, by improving drainage. But the fine root systems of box plants that spread out just below the surface of the soil are particularly vulnerable to drying out. One of the reasons I recommend mulching around the base of box at least once a year. This drying out was made worse by the long hot and dry summer we had here in the UK last year.
If a box plant starts to show signs of red ant activity, then there is still a chance of recovery. First the ants must to be dealt with. I would avoid using ant powders as these are indiscriminate and may contaminate the soil. Small ant traps placed around the base of the box or ant gel are more targeted as the ant carries the poison into nest. Avoid using boiling water as this is a cruel way for ants to meet their end and will damage the box plant’s roots.
Give the box plant a good water when the ants have gone and then mulch around the base with a organic rich compost. Keep the box plant well watered during dry periods but be careful not to over water. Box plants hate having their roots sitting in saturated soil. Apply a foliar feed, such as Topbuxus Health Mix or liquid seaweed extract, every four weeks during the growing season. Hopefully the box plant will soon start to show signs of recovery. If not, then consider replacing in the Autumn. Sick or stressed box plants are vulnerable to diseases like Volutella blight (Pseudonectria buxi) that may affect the rest of the box hedging. So it is sometimes worth replacing rather than trying to recover one sick box plant.
Photo Credit: Red Ants by Michelle Line