Wisteria
Table of Contents
Varieties
Wisterias are large, vigorous climbers that can grow more than 10m in height and width.
They produce stunning, fragrant flowers, usually purple. However, some varieties are blue, and some are white.
The clustered flowers are individually attached to a central stalk at equal distances, called a raceme.
There are multiple varieties of wisteria, with the more commonly grown varieties being Wisteria sinensis, Wisteria floribunda, and Wisteria brachybotrys.
Blooming in mid to late spring, this variety flowers before the leaves appear.
They have blue to lilac flowers.
The stems twine around their supporting structures counterclockwise.
They produce raceme between 15cm - 20cm long.
Flowering in early summer.
Wisteria floribunda produces the longest racemes of all the wisteria varieties.
These come into bloom with the foliage.
The stems twine clockwise around their supports.
Their large racemes usually grow to 30cm - 50cm long, with some cultivars reaching almost 1.5m, which look spectacular hanging from pergolas.
Coming into bloom in late spring
This varity has highly fragrant flowers.
They have shorter racemes, usually 10-15cm long.
This variety twines anti-clockwise around its support.
Wisterias are long-lived, hardy perennial plants. They can easily live 50+ years, with the oldest specimen in England over 200 years old, located at Fuller's Brewery in Chiswick, planted in 1816.
Planting
Plant wisteria in full sun with rich, well-draining soil. Although they will still grow in partial shade, you will get fewer blooms, if any.
Wisteria grown from seed can take many years to flower, if at all. With 15-20 years not uncommon.
Therefore, you should purchase a wisteria grown from a cutting or grafting. These will have a better chance of flowering, although they can still take some time before their first bloom, usually 3-5 years.
Buying a plant that is in flower can give you faster results and minimise disappointment.
Being strong, vigorous climbers, wisterias are not suitable for training into small or light support, like trellises. Train them into sturdy, permanent structures, such as houses or pergolas. Remember, they may one day be over 10m tall and wide. With trunks as thick as small trees! Factor all this in when choosing the right location to plant.
Mature, flowering wisterias can be highly prised and rewarding when trained up the front of a house, but they will require maintenance. Left unchecked, they can cause damage, growing into the guttering, window frames and loose tiles. Fortunately, when following a good pruning routine, they can be problem-free (see Ongoing care section).
Plant wisteria between October and April.
Once you've decided on your location, dig a hole as deep as the container and around two-three times as wide as the root ball. Fertilising is not necessary at this stage. However, ensure you are growing the plant in rich soil.
Backfill the hole, firm and then water.
Ongoing care
Wisterias need attention throughout the year. They are fast-growing, vigorous plants.
When it comes to fertilisers, feed wisterias once a year, in spring, with a high potash fertiliser.
Water regularly, keeping the soil moist, but ensure water can drain, and never allow it to become waterlogged.
The first few years after planting, they can be left unpruned whilst you train them into the support or structures they are growing on.
After they have grown into the supports, prune them twice a year, once in August and again in February.
Prune them first in August. The flowers should be gone by this time.
Firstly, cut the, now flowerless, raments back to the stem.
The next task is to prune all the long whippy growth from this year.
Prune this growth back to five buds, cutting in the direction that the last bud is growing.
This technique will encourage the wood to ripen, where next year's flowers will grow.
Prune the plants again in February.
Further prune the same stems pruned in August. They would have likely grown additional growth since pruning.
This time, prune these shoots down to two buds.
At first, it may seem like excessive pruning, but keeping up this routine should allow the wisteria to put on spectacular blooms.
Pest and diseases
Never allow wisteria to sit in waterlogged soil, as it will become more susceptible to diseases.
Wisterias can be prone to graft failure, and even seemingly healthy plants can be affected. It is due to failure of the graft union and can result in the entire upper section, known as the scion, dying. The rootstock will then likely produce new shoots.
Diseases
Powdery mildew is a fungal disease.
Symptoms of this disease include white powdery spots on leaves. When this disease affects wisteria, it can also cause the leaves to become slightly yellow.
Although powdery mildew is usually not fatal to the plant, controlling the disease is recommended.
Powdery mildew thrives in warm moist conditions. Avoid watering the leaves and ensure good airflow, as this will make the environment less attractive for the fungus.
There are multiple fungicides available to treat the disease. Always read and follow the manufacturer's instructions.
Wisterias can be susceptible to honey fungus, which can prove fatal.
Honey fungus spreads underground and attacks the roots of many woody perennial plants.
Symptoms include dieback of shoots, reduced flowering and discolouration of foliage.
White fungal growth (mycelium) may be visible in the soil and within cracks of the stem near ground level. When honey fungus is suspected, peel back a small section of bark near ground level, checking for mycelium.
Mushrooms may be visible around the plant in autumn. However, they do not always appear, and a lack of them does not mean the fungus is not present.
Mushrooms are usually a honey-like colour, although this can vary.
There are no fungicides available to control this fungus. Once present, you should aim to minimise the spread of the disease. Remove all affected plants and destroy them. Ensure you remove all roots of the plants. Removing soil from the affected area can be advisable. Avoid planting new plants for at least a year where the fungus was present.
The fungus should be unable to survive without a food source for a year.
In addition to honey fungus, wisteria can be susceptible to root rot caused by Phytophthora.
Phytophthora are oomycetes, which are microscopic, fungal-like pathogens.
Above ground, Phytophthora root rot will cause visual symptoms similar to honey fungus, such as dieback, discolouration of foliage and reduced flowering.
You can tell Phytophthora apart from honey fungus below ground as there will be no white fungal growth. However, the roots of the plant will be decaying, becoming softer.
The main reason plants will suffer root rot caused by Phytophthora is waterlogged soil. Preventing waterlogged conditions will greatly reduce the risk of infection.
These microorganisms can stay dormant in the soil for many years.
There are no chemicals available to control this pathogen at home. Aim to reduce the spread of the disease by removing and destroying the affected plants, including their roots, and disposing of the soil.
