Yellow boxwoods

(Question)

I have a boxwood hedge. Several of the boxwoods are still yellow and the foliage is very dry. Is there any way to bring these shrubs back to life.

(Answer)

Boxwood (Buxus sp.) are a very popular shrub for hedges, as they can be shaped easily and look well in a formal garden.  They are also vulnerable to extreme heat or cold and salt damage in the winter.  Completely yellow boxwood after a winter like we have just experienced is not that unusual.

Even though we had a very cold winter, we were fortunate to have some good snow cover to keep upheavals to a minimum.  The problem this year was the timing of the cold – winter started early so water uptake by the plant roots was shortened, as this is what keeps shrubs like Boxwood hydrated through their dormancy period.  Plus, the winter here in Toronto and Southern Ontario was long and extremely cold for an extended period of time.  Hence, dead or damaged shrubs.

Check the shrubs more closely.  Give them a good shake in order to drop any yellow foliage.  Look along the branches – are there green buds?  If not, using your thumbnail, scratch the bark.  If the underbark is green, then that branch is alive.  The problem may be that only the main stem might exhibit life – then you have to prune the shrub back to the live bark.  It won’t look like a hedge anymore.  If you do find this to be so and you choose to prune the individual plants back to live branches, do so now, using clean, sharp and sterilized secateurs.  For esthetic purposes, it is usually wise to prune both sides of the plant so that it looks more pleasing but this will also help generate future even growth.

In my experience, when a boxwood is completely yellow it is dead.  I would dig it out and replace it with a new plant.  It would help if you know the species of boxwood you have so that you can match it as there are many cultivars bred for size and colour.  Otherwise, you will have to figure out which you have and take your chances that you get it right.  For example, ‘Green Velvet’ boxwood gets to about 1 metre in height, 1 metre in width.  ‘Green Mountain’ boxwood is half a metre taller.  Both ‘Green gem’ and ‘Pincushion Korean’ reach only .75 metres in height or width.

Compared to many fancier shrubs, boxwood are relatively inexpensive and are not difficult to find in most local nurseries.  If you purchase new plants, be sure to dig the hole big enough within the hedge row to accomodate the new plant without damaging the roots of the existing hedge plants.  Place the plant in at the same soil level that the shrub is in its pot – no higher, no lower.  The addition of compost mixed with the dug out soil will help get the new plants established.  Loosen the root ball, place the new shrub in its hole, fill with the soil mix, tamp it down and then water it well.  A top dressing of compost or sheep manure along the entire hedge would feed all the plants and also help improve soil structure.  Keep all new shrubs well watered for the next two years, particularly in droughty conditions.  In fact, water the hedge regularly right up to the 2014 freeze up to ensure that plants are better prepared for harsh winter conditions.

As a caveat, if your hedge is along a sidewalk, it is vulnerable to salt damage.  In late fall, protect the hedge with a screen of burlap.  Remove once snow is gone in the spring.