Flower buds not opening on old Rhododendron

(Question)

My old, five foot, Rhododendron has flower buds at the top that are not opening and the plant seems to be making new buds from the old wood about one foot up from the soil?  The Rhododendron beside it is in full bloom at the moment – it is the same variety but is younger and is about three feet tall.  Neither plants are showing signs of disease – browing or leaf drop.  Should I cut it back, wait or just dig it up and throw it out?  I live in the High Park area of Toronto.

 

(Answer)

Both of these plants appear to be healthy but the older of the two seems to be putting its energy into making new buds at the bottom of the plant rather than flowering.  As Rhododendrons bloom on old wood, this plant made its flower buds last year but this year it wants to grow vegetatively instead of opening the flowers.  I think the plant is telling us that it needs a revitalizing pruning as it is old.  There is a myth that Rhododendrons don’t need to be pruned but this is untrue as they are a shrub like any other shurb and need the occasional pruning.

Young Rhododendrons should be pruned to maintain their shape as they mature but old plants like this one may need more dramatic action.  A revitalizing pruning can be done in two ways.

Method one is to cut back one third of the plant each year for the next three years which would ultimately re-shape and rejuvinate the plant.  Cutting must be taken right back to where the new growth buds are.  Always cut about a quarter/half of an inch above the new buds.  This can be done in spring or early sunner but spring is best, right after flowering when new growth is beginning.

Method two is to cut back the entire plant to just above where the new buds are beginning to grow.  Again, cutting a quarter/half of an inch above the buds and in spring or early summer.

In the above scenario, I would suggest method two as the plant is already pushing new growth from below.  This could be done anytime now in the late spring/early summer.  The other Rhododendron beside the ailing one should act as a guide as it is in full bloom at present.  Don’t prune past when the flowering plant has finished blooming.  This would be a good time to carefully prune the younger plant if it needs some gentle re-shaping.

A small word of warning, pruning Rhododendrons does somewhat disrupt their flowering cycle but it is necessary if you are to maintain a healthy plant.  Always use a sharp cutting tool and make clean cuts.  Also, sterilizing tools after use on one plant before using on another plant prevents the spread of disease should that be an issue.