Wisteria floribunda

• Japanese Wisteria

The seed does not exhibit any dormancy habits. It can be sown as soon as it is ripe in a cold frame and should germinate in the spring. Pre-soak stored seed for 24 hours in warm water and then sow in a greenhouse in early spring. The seed can also be sown in an outdoor seedbed in late spring^[6]. Germination should take place in the first spring, though it can sometimes be delayed for another 12 months. Prick out the seedlings into individual pots when they are large enough to handle and grow them on in a cold frame for their first winter. Plant them out in late spring or early summer. Plants are very slow from seed and can take up to 20 years to come into flower^[1].

Basal cuttings of side-shoots in early to mid summer in a frame^[1]. Take the cuttings as soon as the new growth has hardened sufficiently, each cutting should have 2 - 3 leaves^[5]. It can also help to remove a shallow slice of bark from the bottom 15mm of the cutting to expose extra cambium, since this will encourage more callusing and better rooting^[5]. When kept in a mist frame with a bottom heat of 27 - 30°c, they will root within 4 weeks and produce well-established plants by the autumn^[5].

Layering in spring. Simply lay any convenient long shoot along the ground and cover it with a shallow layer of soil. The shoot will readily produce roots at intervals along the stem. When these are well formed, the shoot can be divided up into a number of plants. These should be potted up and kept in a lightly shaded position in a greenhouse until well established and can then be planted out as required.

Prefers a good loamy soil in a sunny south or south-west facing position, sheltered from cold winds and from early morning sun on frosty mornings^[7][1]. Plants can become chlorotic on alkaline soils^[1]. A soil that is too rich results in excessive foliage at the expense of flowering^[1].

Although they are winter hardy to about -20°c^[1], when growing in areas with cool summers the plants require the extra summer warmth of a sunny wall if they are to do well^[8]. Plants can take a few years to settle down after planting out^[9]. Too much shade or too rich a soil are normally the culprits, some form of root restriction can be beneficial^[9]. A vigorous climbing plant, supporting itself by twining around shrubs and trees, though it also succeeds as a free-standing shrub, growing to about 2 metres in height. The shoots twine in a clock-wise direction^[10]. This species is closely related to W. sinensis^[11][6]. Often grown as an ornamental plant, there are many named varieties^[10][1]. The flowers have a strong perfume which can be sweet or musty according to the variety being grown^[5]. The plants flower mainly on short spurs so, if removing unwanted side-branches, it is best to cut them back to 2 - 3 leaves rather than removing them completely since this will encourage the formation of flowering spurs^[5]. Any drastic pruning is best carried out in the spring, immediately after flowering^[5]. Plants are very tolerant of even the most drastic pruning and will re-grow even if cut right back to the base^[5]. Plants are self-fertile and usually produce good crops of seeds in cultivation, there are several cultivars such as 'Geisha' and 'Royal Purple' that are particularly good at this^[5]. Plants in this genus are notably susceptible to honey fungus^[1].

This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby^[1]. The plants also form a symbiotic relationship with a mycorrhizal fungus which makes more water, phosphorus and other minerals available to the plants^[5].