The climbing Hydrangea petiolaris is the perfect plant for shaded walls - even those that face north. The woody stems manage the climbing process by attaching themselves to any wall surface by way of masses of aerial roots. There is rarely any need for trellis or wire supports once the plant has established. It will soon, clothe a wall with bright green foliage, and eventually - masses of creamy white dome-headed hydrangea flowers.
The deciduous nature of the plant brings added pleasure in autumn with its dazzling display of golden yellow foliage before finally losing its leaves. Climbing Hydrangea has added value by way of the attractive bark which peels to bright cinnamon new bark underneath. This is not a sign of disease; simply the plants way of increasing its girth by way of shedding old exterior bark.
Hydrangea petiolaris is a little slow to start, but soon attaches itself and hugs its way upwards and sideways. Its eventual height is the top of the wall! Be patient, for the slow start will develop into around a metre spread in all directions each year.
As it grows upwards and sideways, it rarely spread out far from the framework of main branches – clothing the wall with a not to dense canopy of foliage which will be no more than 30cms from the wall.
In spite of its loving for deep shade, Hydrangea petiolaris will also be happy in partial sun – but avoid the mid day sun which tends to scorch the foliage. It is totally hardy and will withstand hard winters. Its homelands are Korea and Russia with all cold places in between!
Climbing Hydrangea is best against a wall – either brickwork, rendered or even dry stone walling. In spite of the aerial root system of climbing, I have never seen damage to a wall – even a wall with loose or soft lime mortar. It seems that the stems will simply move up to the next firm brick or stone, before using its roots for anchorage.
Bear in mind the ultimate height of the climber, and realise that once it has reached to top of its support (wall) than it can sometimes ‘search’ under eaves of the roof.
One slight problem that can occur – if the climber is planted against an old wall – is that of leaf chlorosis yellowing from the lime that sometimes washes down from the lime mortar. This can lead to a yellowing of the leaves and if severe, browning and leaf loss. Overcome this by annual mulch at the base, using either peat or any organic material.
As with other Hydrangeas, soil type is not too important as long as not inherently high ph level. Bases of walls can often be dry areas, which do not seem to have too much effect on mature plants. Watering at and after planting time is always a good idea.
Growing this plant against a fence or trellis is not the best way forward – neither as a pergola plant. Solid fences are no problem
Larvae of Vine Weevil Beetle can sometimes be troublesome and should be on your list of periodic checks. First sign will be the narrow bites out of the lower leaves as the adult beetles feed.
Normal aphids sometimes bother, but rarely cause severe problems.
Pruning of Hydrangea petiolaris is not normally called for as long as you anticipate the height to which it can grow. Needless to say, any pruning will need a tall ladder!
Easiest way by far, is to carefully remove a few young shoots which are just starting to root against the wall or other support. Alternatively, bend a new shoot to the ground and layer it. Best done in early summer whilst the stems are supple. Softwood tip cuttings can also be rooted in early summer - as can semi ripe cuttings in late summer.