I have noticed that some box plants are more susceptible to box blight than others. This may be down to their variety. Buxus sempervirens ‘Suffruticosa’ is particularly susceptible to box blight. But another important factor is how the box is growing. Healthy, strong box can fight off blight infections far better than weak and stressed plants.
How do you de-stress box? Back massages and soothing music are of little use. So here are a few factors that may help, based on personal experience of working with box over many years rather than any scientific studies or data.
Water regularly through dry periods. Box are thirsty plants and require regular watering in dry spells. Best to water at the base of plants. Watering from above will disperse any box blight fungal spores if they are present. Avoid using overhead irrigation systems for the same reason. Instead install porous drip pipes. These can be attached to a timer on your outdoor tap to ensure your box gets the right amount of moisture, even when you are away. If watering by hand then don’t flood the plants. They will get stressed if sitting in water for any length of time.
Mulch in Spring. Box are woodland plants that enjoy their roots being covered in deep, humus rich soil. They produce a large mass of roots near the surface of the soil that spread out surprisingly far. So ensure a deep layer of mulch is applied to a good width either side of the box plant. Try to mulch every year as soil erosion occurs overtime due to weather conditions and watering. Mulching in Spring benefits the soil by retaining a lot of the moisture collected over the wet winter months. Good soil conditions creates happy and healthy plants. Nothing more stressful for box than having its mass of fibrous roots exposed to the air and drying out.
Don’t trim box when the weather is hot and sunny. This will avoid scorching. In hot weather the wound were the leaves have been cut will not heal. The leaves soon turn yellow and eventually fall off. Cutting on cloudy days, in cooler weather or in the early morning or evening gives the box leaf time to create a protective film across the cut wound and prevents leaf damage. If the box has become sun scorched, the damage is not permanent. The box plants will recover. But having no leaves and using the extra energy to recover is understandably stressful for the plants and will make them more vulnerable to disease.
Give the box space. Using box for structure in herbaceous borders can look wonderful. But try to give the box some space to create air flow around the plants. Crowding creates an environment that blight loves but the box plants find stressful. Trimming can also be very stressful for the topiarist as they tiptoe through tightly planted borders and try to clip the box without inadvertently deadheading all the surrounding flowers! Another important reason not to crowd the box is that it makes it very difficult to clear up the leaf litter after trimming. This is very important to do as box leaf litter and debris harbours box blight fungal spores, increasing the probability of infection (or re-infection).
Feed the box. They are hungry plants during the growing season. Nothing more stressful than trying to grow on an empty stomach. I normally give them a boast with a slow release feed such as Vitax Q4 or Blood, Fish and Bone in early Spring. Work the feed in around the base of the plants but be careful not to damage their mass of fine roots near the surface of the soil. During the growing season (May to September) I spray the box plants every 4 to 6 weeks with a foliar feed such as Topbuxus Health Mix or liquid seaweed. Topbuxus is good as the fertiliser contains copper that hardens the cell structure of the box leaves and stems. This makes the plants much tougher to defend against the fungal spores of box blight. And of course, less stressed.