Wisterias grow well in most soils providing they have plenty of space for root growth.
The flower buds are produced at the base of the previous year's growth so this can make them susceptible to damage by late frosts or cold winds.
To counteract this, they are best planted on a south or west-facing wall.
Similarly, when the plant is grown as a tree, it is better to plant it in a sheltered position.
For best appearance the plant/s should be trained to their allotted space in their first couple of year’s growth i.e. before the main stems mature and become too difficult to move.
To do this, concentrate on establishing equally spaced main branches across the area to be covered by tying the branches into strong trellis or horizontal wires fixed to the wall.
Keep trellis / wires about 50mm (2") from the wall.
Growing as a Tree
Trees should be secured to a stout, upright stake until it is mature enough to self support itself.
Cut back all growths to within two or three buds of the base of the previous year's growth.(see pruning section below)
Sow seed in pots/trays of seed compost and germinate at a temperature of 10°- 13°C (50°-55°F)
Pot the seedlings into 75mm (3") pots of potting compost, and grow on in a cold frame.
Layer suitable strong shoots / stems.
The layers will root within a year.
Pot on seedlings into 150mm (6") and grow on in the cold frame until planting out time.
Where large specimens need to be controlled, cut the season's young growth back to within five or six buds of its base. (See pruning section below)
Continue training plants as new growth forms.
Take 75-100mm heel or nodal cuttings from the base of the current year's wood.
Insert them in a 50-50 mix by volume of peat and sharp sand and place in a propagator set at 16°C (60°F) to root.
Once rooted pot up into 100mm (4") pots of potting compost and grow in a cold frame until planting out time.
Plant out young pot grown plants now or wait till circa Week 14.
Provide a permanent support and tie the growths to it until the twining stems can gain a firm hold.
Train Wisterias from an early age, otherwise the shoots rapidly become twisted and impossible to deal with as the wood firms up.
Space the main growths of recently planted plants about 200mm (8”) apart, tying these in to pillars, pergolas or supporting wall wires.
Cut back laterals,(side growths) on established main stems to 150mm (6”) long.
This can be done in either, one operation, or over a period of about three weeks.
Reduce to two or three buds next winter.
Lack of flowers: there are several reasons why this may occur.
Recently planted wisteria may take a few years to settle down before flowering.
Named cultivars are propagated by grafting onto rootstocks, and sometimes the graft can fail.
If this is the case, there is not much you can do about it other than to replace the plant.
When buying plants, check for a healthy graft union, you should see clear join 150-300mm (6”-12”) above soil level.
After planting prune out all shoots that arise from below this point.
If the plants were raised from seed they will take many years to flower.
This situation can be further aggravated if plants are in the wrong location: Wisterias need a bright, sheltered spot to flower well.
Quite often they are planted too close to a building or wall resulting in dry conditions at the roots.
To retain soil moisture and help prevent bud drop the following year, mulch in spring and water in dry spells, especially from late July to September when flower buds form.
Conversely plants in shady positions may lack flowers.
Try and improve light levels with the aid of reflective surfaces.
Soil: some soils they may be lacking nutrients.
Circa week 16-18:
Apply super-phosphate at a rate of 70gms (2oz) per sq m and sulphate of potash at 35gms (1oz) per sq m.
Frost: flower buds may fall off in fluctuating day and night temperatures.
Wisteria flower more freely if pruned to restrict growth.
Once the basic framework has been established, you can begin pruning to maximise flower production, this is generally carried out twice a year.
Circa week 28-35:
Tie in new shoots as required, then shorten the current season's shoots back to 300mm (12”) long, this allows a spur system to develop, the wood to ripen, and ultimately encourage flower bud formation.
Any whippy shoots that grow after this pruning should be cut back to five or six buds from the main branch, make the cut just above a bud.
Circa week 8-10:
The following year, these same shoots can be pruned back to leave two or three buds, this action should form a spur around 50mm (2") long.
It should be possible to distinguish the flower buds from the growth buds as these are larger and more rounded than the thinner, more pointed growth buds.
If major pruning is required to mature plants that have been neglected, then stagger renovation over several years.
All parts of the plant are poisonous including the flowers and seeds.