Horticulture Hacks: Pruning your Wisteria
August 5, 2020
Nurtured in Norfolk’s gardening expert Martyn Davey answers all your questions and gives his top horticulture hacks.
If you would like any horticulture query answered please do e-mail our head grower at email@example.com to add your thoughts to our horticulture hacks.
Could you please give me some advice on how to prune my wisteria. I bought it a couple of years ago from a reputable garden centre and I was told that it would flower the next year or two as it was already grown from flowering stock (I am not sure what that means) but as yet I have not had any flowers on it and I hope that you can give me some help with how to prune it for flower. When I planted it in the garden I made a large hole and filled it with compost and watered it in, it has established well but seems to be getting a bit unruly.
Mrs C Bradley, Attleborough
Wisterias do best in well-drained, fertile soil, in full sun. They are native to China, Japan and eastern United States and, of the ten species; the three most commonly grown are Wisteria floribunda (Japanese wisteria), Wisteria sinensis (Chinese wisteria) and Wisteria brachybotrys (silky wisteria). All three species are strong-growing and capable of reaching around 10m in trees or spread up to 20m against a wall. Certainly it would be worth knowing which species yours is -this will help with the care of it.
Wisteria has a reputation for being difficult to prune but this isn’t the case. Once you have established the routine of pruning your wisteria twice a year, you should be rewarded with a good display of flowers. Regular pruning means shortening the excessive whippy growth in July/August to five to six leaves, about 30cm. This allows the wood to ripen and improves the chances of flower buds forming. Then, in February, further shorten these shoots to two to three buds, about 10cm, to tidy the plant before the growing season begins to allow the new flowers to be seen.
Leave your young wisteria un-pruned until it has covered the wall or garden structure and then begin the regular pruning to encourage flowering. Wisteria can be trained to grow up into the canopy of a small tree, but this may damage the tree over time. If grown into a large tree, pruning will be difficult and the flowering will be affected if the leaf canopy is dense.
Poor flowering is one of the most common problems experienced with Wisteria and this can be caused by a number of things, young plants can take up to 20 years to flower so avoid disappointment by buying a plant in flower or choosing a named cultivar as they are usually grafted. Check your pruning technique and timing as pruning in early and midsummer will disrupt the formation of flowers for the following year. Wisteria flowers best in full sun, with few if any flowers forming in deep shade. Water your wisteria during dry spells between July to September as a shortage of water at this time will effect flower bud formation for the following year. Spring frosts can damage or distort developing flowers and cause the buds to drop before they open. Poor soils may be short of potassium, so apply sulphate of potash in spring to promote flower formation for the following year. Shredded flowers or tell-tale teeth marks are signs of damage by pigeons or mice.
Plants will dry out quickly on light or sandy soil so keep them well watered, particularly when newly planted and in dry periods. Feed your wisteria in spring with Growmore or Fish, Blood and Bone at the recommended rate shown on the packet. In sandy soils (which have low potassium levels) also apply sulphate of potash at 20g per sq m. You can also use rose or flowering shrub fertilisers.
Horticulture Hacks: Jobs for this week
- With the very hot dry weather watering is one of the most important jobs in the garden, containers will need watering every day in the evening is the best time to do this and use grey water or from rainwater butt if possible.
- To prolong flowering remove dead flowers from summer bedding and perennials.
- Save seed from your favourite plants to sow next year, keep in a paper envelope and write the plant name and date of collection on the envelope, if you are like me you will forget.