Boxwood | Buxus Care & Box Blight
Boxwood is one of the best plants for low hedges and topiary. It is slow growing, and suits a wide range of conditions. It is easy to look after, and you can trim it into almost any shape.
Unfortunately Buxus, like all plants, is susceptible to a few problems including Box blight. Here are some simple tips to avoid problems developing and how to manage or fix them if they arise.
Right plant, right place
Buxus grows in sun or shade, but they are more susceptible to diseases in warm, wet conditions: ie when plants are wet all day and don’t get a chance to dry out. Don’t plant Buxus in a damp location; and choose the most robust and disease resistant varieties available. Buxus “Green Gem” is one of the best varieties. Buxus suffructicosa is one of the worst varieties.
See attached test results on various Buxus varieties, conducted by the Department of Plant Pathology, North Carolina State University.
Keep plants fit & healthy
Keep plants well fed, watered and healthy and they will be better able to fight off problems. Buxus are like roses, and need generous amount of food and an average amount of water.
Water activates fertilisers. Keep plants well watered, but don’t over water. Always water at the base of the plants, and never the foliage.
Prune at the right time of year, and keep tools clean
Buxus is slow growing and I trim twice a year: in August before they put on their spring growth, and after Xmas when the tender light green foliage has hardened off and turned dark green.
Only trim on fine days, when all the foliage is dried out and rain isn’t forecast
Keep tools clean. I dunk my snips in diluted household disinfectant as I am trimming, to minimize the risk of spreading any infections
Spray immediately after trimming with copper, to minimize the spread of disease in the cuts.
Overall orange colour, orange or yellow edges of leaves
This is a symptom of stress, and may be caused by a lack of nutrients or water. Plants in pots are more susceptible to these types of problems. To cure - follow feeding & watering regime above. You can also trim the roots, freshen up your potting mix and re-pot every few years.
Black sooty mold
This is a symptom of scale – a limpet like sap sucking insect. Spray per directions with a systemic insecticide like Orthene or Confidor.
Box blights: leaf drop and black lesions on the stems
Sometimes dead branches are a symptoms of dogs urinating on the plants, or broken branches from heavy wind, kids and animals playing in the garden.
Take a closer look: if there are black lesions / streaks on the stems then the problem will probably be a bacterial or fungal infection, and in worst cases it may be Box blight.
For minor bacterial or fungal infections - remove the plant or infected parts, dispose of offsite and clean your tools. Give your plant a boost with a fast acting strong fertiliser like BioPhos and Nitrophoska Blue.
One of the causes, Volutella buxi, has been around for a long time. The plant is generally not killed and the leaves can grow back – but you have to be careful it doesn’t become widespread, unsightly and ultimately damaging. It enters the plant through wounds and cut stems. Fallen leaves can also carry the disease over the winter and new spores are produced in spring. This is why it's important to spray with Copper after pruning, to keep your tools clean, not to prune on a wet day, and to pick up your cuttings.
Another cause Box blight, Cylindrocladium buxicola, is air born and tends to strike plants in still, wet conditions. It is becoming more prevalent in Auckland, and is heading south. It has similar symptoms to Volutella buxi above, but a more devastating/widespread impact. It is airborne and tends to spread more quickly, and can wipe out a whole hedge rather than parts or nearby plants. Note the two problems can present together.
In both cases, NZ’s top garden owners Melanie Greenwood and Alan Trott recommend a spray called Mancozeb as a preventative and cure. This is available in bulk through rural and horticultural suppliers. Another spray is also available in smaller, more manageable quantities for home gardeners through garden centres. It is called Box Blight Buster by KiwiCare, and has been licensed for sale as effective against Box Blight.
If you want to avoid these sorts of chemical sprays, organic gardener Wally Richards suggests the thinning of internal branches to increase air circulation; and spraying every 3 months with Vaporgard. Complete coverage with Vaporgard should put a film on the plants and stop the spores from settling and taking hold. Remember some varieties are more disease resistant than others like Buxus “Green Gem”, which has a more open internal branch structure.
Other options include taking out and disposing of the infected Buxus plants, and replacing them with a different plant altogether (if only it were that easy!) In this regard, I note we have a range of topiaries available in Corokias and other hedging plants.