Pruning and Deadheading

Remember to wear gloves when handling any part of laburnum.

Laburnum falls into RHS pruning group 1, which means no pruning is required if being left to grow freely as a specimen tree other than the occasional removing of dead, diseased, damaged, or badly placed growth. This is best done between late summer and Christmas; laburnum is likely to bleed sap if pruned in spring or early summer.

Some laburnum cultivars may be grafted onto the rootstock of another species. If this is the case, remove any shoots arising from below the graft union whenever you spot them.

If you’re training a laburnum, the shoots will need to be tied in and trimmed as follows:  

• Tie main shoots to the support throughout the growing season.
• Until the main framework is established, trim the main shoots back by a third between the end of summer and midwinter. This will encourage bushiness and therefore a dense coverage of the support. Any unwanted shoots can be cut back to three to four buds.
• Continue to do this until the framework is established. After this, simply shorten back all shoots annually to retain the shape.

Watering

Like all woody plants, laburnum does best with regular watering for its first couple of growing seasons in the ground to encourage root establishment. After this it should be largely self-sufficient, though it still pays to water in prolonged periods of hot, dry weather. An annual mulch is also useful for locking in moisture – more on this in our ‘Feeding’ section below. 

Container-grown laburnum needs regular watering throughout every growing season. Aim for infrequent big soakings, rather than little and often, allowing the top few centimetres of compost to dry out each time, though be aware that container-grown trees can dry out very quickly during the height of summer and sometimes need watering as often as every day. From mid-autumn, the British climate tends to take over watering needs, though do remember to step in in the event of an unseasonably dry spell.

Feeding

On healthy, fertile soil, an annual mulch of well-rotted organic matter should provide sufficient nutrients for your laburnum. This has the added benefit of suppressing weeds and locking in moisture. Autumn or spring are the best times to carry out mulching.  

For an extra boost (most needed in the first few years of the plant being in the ground, or annually if growing in poor soil), apply a general-purpose granular feed or blood, fish, and bone to the surface of the soil and lightly work it in. This is known as a ‘top dress’ and is best done in late winter or early spring.

Container-grown plants rely more on the gardener for nutrition. Get off to a flying start by making sure you use a good quality potting compost, then throughout the growing season (March to September) apply a liquid feed every 3-4 weeks. Remember to repot into a slightly larger pot with fresh compost every few years. Once the plant is in the largest container possible and this is no longer feasible, an annual topdress is advised. Each spring, scrape away the top 5cm of compost and replace with fresh, remembering to mix in a little general-purpose slow-release feed. 

Cold Protection

Laburnum is hardy enough to withstand even a harsh UK winter without the need for additional protection. Having said this, flower buds can be damaged by a late frost, so where possible try to plant in a sheltered spot. Otherwise, young or small trees can be protected by one of these handy fleece jackets, a layer of horticultural fleece, or old bedsheet. Mature specimens can be harder to protect; though you could take inspiration from RHS Wisley, where the garden team stoke nighttime fires beneath the laburnum arch whenever a late frost is forecast.

Pests and Diseases

Laburnum is a relatively problem-free tree, though you may spot the work of the laburnum leaf mining moth. In its caterpillar form this can cause unsightly blotches on the leaves, though rarely affects the overall health of the tree. Tolerate if you can, leaving natural predators such as blue tits to keep numbers down.

Other potential pitfalls include honey fungus (mercifully rare unless you’re near a heavily wooded area), blackfly, and powdery mildew. While there’s little you can do to avoid honey fungus, the effects of blackfly and powdery mildew can be mitigated by growing as healthy and thriving a tree as possible. This means planting it in the right conditions, keeping it watered until fully established, and mulching annually. Encouraging a balanced garden ecosystem also helps control pest numbers. This can be done by limiting your use of chemicals, feeding birds, planting a rich and diverse range of plants, and leaving some areas a little more ‘wild’ to provide a habitat for wildlife.