Wisteria plants originally grew on trees with the roots embedded in the forest floor in the rich organic matter of the leaf litter created by autumn leaf falls. The top growth of the plant grows strongly upward to reach the light.
To grow wisteria successfully you need to re-create these conditions in the original planting and the yearly maintenance. When planting you should select a position that has the roots in a shaded spot, but will allow wisteria’s top growth to find the sun against a wall or fence.
Dig a large hole and fork the base, incorporating large amounts of organic matter, such as garden compost, farmyard or stable manure. Make sure that you only use well-rotted manure and compost, as freshly made can burn the roots of the new plant.
With the yearly maintenance of the wisteria you will need to add additional organic matter by top dressing the plant’s base in the spring. Feeding with a general garden fertiliser such as Grow More can be carried out in the spring followed by feeding with a liquid tomato feed every 14 days after the end of May.
Wisterias flower from flowering spurs that form on the stems. The best way to encourage the development of the spurs is to train your wisteria so that the side shoots and branches are horizontal.
The best form of training is on a wire secured to a wall or fence using wine eyes and galvanised wire. Naturally wisteria plants climb by sending out shoots that look for tree branches to climb on.
Once a branch is located the wisteria stem starts turning clockwise in a circling motion resulting in a coiling to secure its new position. This fact is worth remembering when training your plant to a new wire as twisting the stems in a anti-clockwise direction will cause the plant to waste a great deal of energy and time untwisting and re-twisting itself.
With your wisteria trained, light summer pruning should take place during the first three summers to control any wild side shoots that you do not wish to tie in and to reduce any excessive foliage.
If you have had a wisteria for a number of years that has failed to flower, it is time for some drastic measures. In late autumn after the leaves have fallen you should prune the plant back by 50% removing all the thinner stems, only leaving the main plant structure. Test the soil to see if it is alkaline and if it is add a small dressing of iron sulphate to help counteract this and help turn the soil slightly acid.
Finally, top dress with some organic matter around the base. In some cases you will find that even this drastic pruning will not result in flowering because the plant has been planted incorrectly in the first place with no organic matter, or it had been propagated from a parent plant that also lacked flowers.
The only solution at this stage is to re-plant with a new plant, which you know to have been propagated from a prolific flowering parent.