How to Grow Wisteria
Wisteria is a deciduous, twining climbing plant which will flower for several weeks and many varieties carry a lovely scent. A Wisteria in bloom is a magnificent sight with long, trailing scented blooms which are either blue, purple, pink or white. Ideally, Wisteria is best suited to and traditionally grown up a south facing wall. Wisteria rewards well, a beautiful climber flowering between April and June.
If Wisteria is growing well and happy in its spot, you may also get a second flush of weaker flowers in late summer around August time. I find this causes a bit of a pruning dilemma as those flowers can be where you want to prune and I hate to cut them off. Delaying pruning by a couple of weeks will make no difference in the long term .
Wisteria is vigorous growing up to 9 meters (30ft) which means it needs a large space. It is not self supporting and requires a framework or wires or supports to grow up. Although Wisteria grows well in sun, and in full sun, it will also tolerate light shade. The downside to growing Wisteria is that it is a demanding plant to grow in terms of time and attention required which makes it a red wheelbarrow plant.
There are no difficulties in getting Wisteria to grow because it is a vigorous climber; the trick is to get it to flower, (see below) When planting Wisteria, it is essential to have a framework for the plant to climb up, which is secured with wires tied into the wall and hooks. The frame work is best put in place before the Wisteria is planted. Wisteria floribunda (which twines clockwise) is originally from Japan, and w.sinensis ( twines anti clockwise ) is from China and is the more vigorous of the two. On W.senensis the flowers appear before foliage, and on W.floribunda flowers and foliage come out at the same time.
Wisteria needs to be pruned twice a year, (summer and Winter) to ensure it flowers consistently each year. As the Wisteria matures it grows further up the wall, ladders are needed for pruning which does make it high maintenance and definitely a red wheelbarrow plant. Wisteria is vigorous and although it can be pruned to keep in size, it still needs a large space. It may sound obvious, Wisteria is best planted in the right place from the outset. This is because it forms very strong, woody roots and is hard to remove once established.
Wisteria blooms (racemes) come in soft shades of violets, pink and white. Suggested good varieties are: Wisteria floribunda 'Multijuga' which has scented racemes up to 1m long and is an attractive lilac colour and with the RHS garden merit award. A good pink variety is Wisteria floribunda 'Rosea' racemes up to 60cms long, scented and pale pink Wisteria floribunda 'Alba' is slightly less vigorous with white scented racemes up to 60cm and scented The traditional Wisteria sinensis has strong colour and fragrance. If you have a large space and are looking for a striking garden feature, I have seen Wisteria combined with Laburnum growing over an archway to create a tunnel of lilac and yellow. Word of warning: Laburnum is poisonous and the seeds highly toxic so not a plant suitable for a garden accessed by pets or children.
How to Make Wisteria Flower
It is a member of the legume family, it does not need feeding generally speaking and will fix it's own nitrogen. Sparrows are partial to the buds but don't usually eat all of them so if your Wisteria does not flower the chances are it is either a poor plant or lack of pruning. These two points are the main cause of lack of flowering.
Buy A Wisteria plant in Spring and In flower
If you want your Wisteria to flower, buy a Wisteria plant in the spring which is in flower or with flower buds on it. That way you know it can flower. The image above left shows a small newly planted Wisteria with some small flowers on it. This Wisteria was newly planted in 2007 and within 7 years had reached a height of 3.5m or around 12ft and the little plant in the image above expanded in 7 years to the second image. This is as a reminder that Wisteria are vigorous and the taller it gets, the longer the ladders needed to prune it.
Wisteria should be purchased as a grafted plant, and you are likely to have problems with any plant grown from seed which maybe cheaper, but it may take a very long time to flower. You can generally spot a grafted plant as there is a bulge in the stem just above soil level in the plant pot. Equally, the retailer should know and plants offered for sale are often stated to be grafted plants
When planting a new Wisteria water it well and ensure that it does not dry out. Once established it will be fine but to start with if there is a dry spell it will need watering. Grow in a sunny spot in full sun. Wisteria are fully hardy but the emerging flowers (racemes) can be damaged by frost so a more sheltered spot is best and traditionally against a south facing wall training the Wisteria to fan out across the wall. Wisteria are usually easy to establish, fast growing and need a lot of space, and time. Wisteria can be grown as a standard if space is limited which will involve careful pruning. If Wisteria is grown in a container it will need a lot of watering.
How to Prune Wisteria
As Wisteria is vigorous, if it is not pruned regularly it will very quickly become rampant and outgrow it's allotted space. In addition, plants need to be trained horizontally which aids flowering.
How to Prune Wisteria - Winter Prune
In the winter prune, you are shortening the spurs and in the summer prune removing leafy growth; two different types of pruning.
In some ways the winter prune is easier because you can see the framework of the Wisteria. Winter pruning is best done in February, on a mild day, and you will need ladders to access all of the plant. In the winter prune you need to cut the shoots back to 3/4 buds reducing to 8/10 cms (3-4") Aim to leave the main plant framework in place and prune the shoots coming off the main frame work to encourage the formation of spurs.
How to Prune Wisteria - Summer Prune
The summer pruning is just as essential and it is best to prune hard. The purpose of the summer prune is to restrict, and cut back the vigorous growth, so the plant will throw out flower shoots in the spring. Again, taking into account the main frame work, and where you want the plant to grow, cut back the long wippy (soft) growth to about 15cmc (6") Leave unpruned that which is needed for the frame work.
You may need to cut off a lot of the long wippy growth, and also cut off all laterals which appear at the base of the plant. These are shoots being thrown out a the base and remove them all.
Pruning twice per year is essential for flowering and as the plant grows its high maintenance, in both senses. Hard work and step ladders are needed.
Thanks to Helen Yemm writing in her excellent gardening column who remarked on the staining caused by Wisteria sap. It leaves brown marks on your clothes which nothing will shift. Most important then to be in your oldest gardening scruffs for this job.
A final small point on the time and maintenance required by Wisteria, as a plant it drops a lot of leaves in November and December which also takes some maintenance clearing them up.
Frost Damage on Wisteria
Frost can just occasionally cause problems. The Wisteria shown on this left has been growing and flowering happily for 10 years without any real problems. However the Spring of 2017 had unusual weather conditions, mostly it was drier than usual, and often warm, which advanced the growing season and the Wisteria was into full bud when in mid April a very cold spell struck with both ground and air frosts in many parts of the country. The winegrowers in the south of England reported 75% damage to their crop after temperatures dropped to -5. Frost doesn't do Wisteria any good either as the image left shows. Some buds have flowered, but others as illustrated in the image have been severely damaged and will not flower. It is disappointing, because only about half the Wisteria will flower although not fatal. Wisteria is tough and it will come back next year and there may even be a second flush of flowers in August, depending on the weather, as always.