Wisteria in May: monthly care

Once established, wisteria is fairly drought-tolerant but performs best with moderate, consistent watering. Water deeply during prolonged dry spells in spring and summer, especially while flower buds are forming, but avoid waterlogging—wisteria roots rot in saturated soil. Reduce watering in autumn and winter when the plant is dormant. A 5 cm mulch layer of compost or bark applied in spring helps retain moisture and suppress weeds, but keep it away from the stem. Feed sparingly. Wisteria is a member of the pea family (Fabaceae) and fixes its own nitrogen, so high-nitrogen fertilisers produce lush foliage at the expense of flowers. In March, apply a potassium-rich fertiliser such as sulphate of potash or a tomato feed to encourage blooming. A single annual feed is sufficient; over-feeding is a common cause of non-flowering wisterias. Wisteria is fully hardy across zones 5a–9b and needs no winter protection in temperate Europe. Check supports and ties annually—mature plants are immensely heavy and can pull down weak structures or damage guttering and roof tiles. Inspect for loose stems after winter gales and re-tie as needed. Pests are rarely serious. Aphids may cluster on soft new growth in spring; a strong jet of water usually dislodges them, or use an insecticidal soap if necessary. Wisteria scale can appear as brown lumps on stems; scrape off by hand or treat with a winter wash. Honey fungus is the most serious disease risk, causing dieback; affected plants usually need removal. Poor flowering is almost always due to insufficient sun, over-feeding, or lack of pruning rather than pests or disease.