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Wisteria

Even if you don’t live in a region where wisteria is hardy, you’re probably familiar with these lovely fast-growing vines. The plants are known for their hanging clusters of pink, purple, white, or blue pea like flowers. Flowers are fragrant and give way to pods of seeds.

Plant facts

Common name: Wisteria
Botanical name: Wisteria spp.
Zones: 4 to 9, depending on species
Size: Climb to 30 feet or more
From: Areas of Asia and North America, depending on species
Family: Fabaceae, the pea family

Growing conditions

Sun: Plant wisteria in full sun with at least 6 hours of direct sun each day.

Soil: The soil must remain moist and well drained. If soil is high in sand or clay, amend it with organic matter before planting. The more organic matter, the better.

Moisture: Water wisteria in times of drought.

Care

Mulch: Place a layer of mulch around the base of the plant to keep weeds at bay, conserve moisture, and maintain consistent soil temperatures. Leave a 4-inch gap between the mulch and the wisteria’s trunk.

Pruning: Pruning keeps these large vines in check. To encourage flowering shoots, cut the newest side shoots back about 6 inches from the main branch in midsummer. In winter, prune the regrowth back to about three nodes (leaves) from their main branch. This will help encourage the growth of flowering shoots in spring.

Fertiliser: In average soil, wisteria doesn’t require fertilisation. Too much fertiliser can inhibit blooms.

Support: These vines need a sturdy structure for support because they can easily reach 30 feet or more.

Propagation

Seed: Soak seeds in warm water for 24 to 36 hours. Plant them outdoors in a sheltered spot in the garden or in a moist seed-starting mix. Germination can take a month or more. Wisteria started from seed can take many years to bloom and may be inferior plants compared to cultivars.

Cuttings: Take softwood cuttings in spring or early summer. Cuttings root in about eight weeks.

Layering: Bend one of the growing shoots toward the ground in early spring. Remove the leaves along a section of the stem, gently nick the stem in that area, then bury that section under several inches of soil. Anchor the shoot to the ground. The stem should root in about a year. After it roots, cut it from the mother plant.

Pests

Aphids: These small insects often appear in large numbers on new growth. Spray them off daily with a stream of water; they will not attack a plant after being knocked off. Use an insecticidal soap or neem-oil spray if infestations are severe.

Japanese beetles: These large, dark-coloured beetles chew holes in leaves. If infestations are severe, try an insecticide made from neem. Immature Japanese beetles are white grubs that eat plant roots. To reduce the number of grubs, use a grub killer or a bacterium called milky spore.

Leaf-miners: Leaf-miners are small flies. Their larvae burrow tunnels in plant leaves. In most cases, the damage affects only the look of the plant, not the plant’s health. Remove and destroy any infected leaves. Keep a layer of mulch around the plant to help prevent leaf-miners from burrowing into the soil, where they pupate and become adult flies.

Scale insects: Scale insects look like tiny disks on plant stems or roots. They suck juices from plant cells. Encourage beneficial insects, such as wasps, or use horticultural oil.

Viruses: A few viruses can infect wisteria. They often cause a decrease in vigour, malformed new growth, and a mosaic pattern of discolouration on leaves. Unfortunately, once a plant is infected with a virus, there’s no saving it-it’s best to destroy the plant.

Fungal disease: Fungal diseases occur when the plant is in a spot that’s too wet. Once a plant is infected with a fungal disease, there’s little you can do to stop the disease. To prevent fungal diseases, prune vines to encourage good airflow, plant wisteria in well-drained soil, and keep the foliage dry. Prune infected leaves or branches to help keep the disease from spreading. Destroy any infected leaves that fall to the ground.

Leaf spot: Many leaf spotting diseases appear as discoloured spots on leaf surfaces made up of concentric circles, forming a tiny bull’s-eye pattern.
Powdery mildew: This disease first appears as discoloured spots on plant leaves. As it progresses, the leaves become covered with a grey powder and drop off.

Garden notes

• Most parts of the wisteria plant, especially the seeds, are poisonous to people and animals.
• Some types of wisteria (Wisteria floribunda and W. sinensis) are considered invasive in certain parts of the country. Check with local authorities before planting a wisteria.
• Wisteria vines cannot climb walls-they need an arbor, trellis, flagpole, or similar structure for support.

Some gardeners try to train their wisterias as standards, or trees. This takes intensive pruning, as well as a very sturdy stake for the vine’s “trunk.”

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