One of the frequently searched articles on our website is a piece I wrote a while ago on buxus blight (aka: why is my box hedging turning brown and looking as if it is dead and what can I do to resurrect it?) Given that we are a bit sniffy about box hedging here, it seems ironic that we are apparently seen as a source of information on the matter. Mind you, in deference to the level of interest and concern from others about both the short term look and the long term viability of their box hedging, I have been taking a slightly more than desultory interest in the whole matter.
You too can google it if you have some level of computer literacy and it is likely that you will come to the same conclusions from the international research and the anecdotes that I have. There are certain incontrovertible facts: it is a fungus called cylindrocladium and its rate of multiplication does not appear to be temperature related – in other words, it will multiply quickly in cold temperatures too. Most fungi thrive in warm, moist conditions but nasty buxus blight appears to be quite well adapted to cool and even dry conditions. The fungi spores are long-lived and can survive for years on dead leaves.
There are around 30 different species of buxus originating from Europe, Asia, the Americas and even North Africa. I have been told by individuals that the Asian forms from Japan and Korea (Buxus microphylla and microphylla var. koreana or Buxus sinica) don’t get it but the scientific evidence does not back this up. It is likely that the personal anecdote is based on the fact that in one particular location, this type of buxus is not showing signs of infection. That does not mean it won’t be affected in another location and the research says none are immune. The bottom line is that I wouldn’t be ripping out affected sempervirens (and suffruticosa, the very low and slow form used as an edger is still a sempervirens variation and is particularly susceptible) and replacing it with a different species of buxus, be it from Japan, Korea or anywhere else. I would be wanting to use a totally different plant family altogether.
You will know if you have buxus blight. Small dead patches are more likely to be dog urine or an accidental whiff of glyphosate. Buxus blight is simply devastating. The dead patches spread rapidly and do not show any willingness to regrow.
The first bit of bad news is that if you have buxus blight already, you will have to spray endlessly, for the rest of the buxus life, to keep the blight at bay because you won’t ever eliminate all the fungal spores. You can manage some level of control but the days when all your handy little hedge needed was clipping twice a year are over.
The second bit of bad news is that if you live in an urban area and do not yet have buxus blight, it is probably only a matter of time before you will get it because the fungal spores are easily dispersed by wind, so will gently spread throughout built up areas where there are host plants at regular intervals. You can reduce your chances of getting it but you are doing a King Canute number.
The good news is that if you live in the country and none of your neighbours have buxus blight, you may be able to keep it out because the spore don’t seem to be travelling quite as far as, say, camellia petal blight spore which have been tracked up to 5km. But quarantine your garden. Don’t bring in buxus plants or cuttings from other places unless you are 100% sure that the source is isolated and free of blight. Propagate your own additional plants at home. The international advice is that you should routinely quarantine all buxus plants brought in from other sites until you are sure they are free from blight. The problem is that quarantining plants at home is difficult. They need to be confined to a shed, glasshouse or nova house for an extended period of time and few people have the facilities to quarantine effectively which means that if by any chance the plants or cuttings you have brought in are harbouring the fungi, even if you try and keep them separate the spore will spread. Easier by far to seal your garden borders and not admit any foreign buxus. They are dead easy to propagate at home for even the most amateur gardener.
If you have masses of box hedging or topiary in your garden that you want to try and keep, you probably have to accept that it is going to take more work. Don’t let the hedge get too dense – there appears to be a connection between the ability of the plant to shed water quickly and slowing the fungal spread. Avoid overhead irrigation. Keep thinning the plants so they are not too dense and get as much of the build up of dry leaves and sticks out of the centre as possible to allow more air movement. There is some evidence that copper sprays will at least slow down the fungal spores and copper may be kinder to the environment than most anti-fungal sprays. It may be worth trying sulphur sprays too because sulphur has anti fungal properties. An all round rose spray may be effective if you are willing to treat your buxus hedge like your hybrid tea roses.
The big problem is what you can use instead of the infinitely useful buxus. There are three stand out characteristics of buxus. Number one is that you can keep it looking tidy on two clips a year and it does not grow too fast. Number two is that if you hard prune back to bare wood, it will resprout so you don’t end up with woody legs. Number three is that it roots so easily it is a doddle for the home gardener to produce and correspondingly cheap(ish) to buy. And we could add numbers four and five– that it is long lived and a good dark green. We are of the general opinion that hedges should be green. The problem is finding a substitute which meets all the above characteristics. Lonicera and teucrium are cheap and clip well but grow so rampantly that you have to clip frequently to keep them looking sharp. Small leafed camellias and totara clip really well and resprout from bare wood but are not easy to propagate so are much dearer to buy . Some of the small leafed hebes may clip well (but some don’t so you have to get your variety right) and root easily but are not always long lived. Pittosporums grow too well and get too tall too fast and tend to be a pale green in colour, not the desired dark shading. And they have larger leaves. Corokia can get a bit bare over time. Griselinia tend to have large leaves. Taxus (yew trees) are notoriously short lived in our climate because the roots get phytopthera. The biggest gap of all is the lack of a clear replacement for the dwarf suffriticosa which is used where a low edger is desired.
There is no like for like swap for box hedging. In the end, if box hedging features large in your garden and you have to cut your losses on it because of buxus blight, you may be wiser to go back to the drawing board and look at garden plans which don’t depend on clipped and well behaved little hedges for structure. We are mulling around the role filled by buxus hedging and will return with more thoughts on this in the future.