Also known as the golden rain tree, the laburnum produces bright green foliage that gives way to showy yellow panicles that measure 25 cm (10 inches) in length. This fast grower enjoys full to partial sun and well-drained soil. The laburnum thrives in the UK's climate, reaching heights of approximately 6 metres (20 feet) with an equal branch spread at maturity. Laburnum trees propagate by seed, which require a cold stratification period before sprouting in the spring.
Prepare a sunny location for fall planting, just before the ground freezes. Choose a location that contains well-drained soil with a soil pH between 5.0 and 6.5. Test the pH of the soil using a testing kit.
Loosen a 45 cm (18 inch) square of soil, to a 45 cm (18 inch) depth using a garden fork. Amend the soil if the pH is above 6.5, using peat moss. Add lime if the pH is below 5.0. Refer to the manufacturer's instructions on the packet label for application methods.
Place three to four laburnum tree seeds in a cup of warm water. Allow the seeds to soak for 24 hours. Remove the laburnum seeds from the water after the soaking period and place them on a paper towel.
Press the laburnum seeds into the soil at a depth of 1.25 cm (1/4 inch). Separate the seeds approximately 2.5 cm (1 inch) apart. Pat the soil over the seeds to remove air pockets. Water the soil to a depth of 2.5 cm (1 inch) using a garden hose.
Cut a 45 cm (18 inch) square piece of screening using a sharp pair of scissors. Set the screen over the planting area and secure each corner with a fist-sized stone. Spread a 7.5 cm (3 inch) layer of bark mulch over the planting area. The mulch will disguise the screen and also improve drainage in the planting area. Mulching also protects the laburnum seeds from the winter freeze.
Water the soil weekly, providing at least 2.5 cm (1 inch) of water per week in lieu of rain. Resume watering in the spring when the ground thaws. Do not over soak the soil or the seeds will rot. If the soil feels moist to a 2.5 cm (1 inch) depth, there is no need to run the garden hose.
Continue to maintain moist soil with supplementary watering in the spring. The seeds should sprout in the early spring, peaking their way out of the soil upon germination. Pluck-out the weakest seedlings and discard once they all develop their second set of leaves. Leave the healthiest laburnum seedling to grow in the soil.
Once the laburnum seedling reaches a height of 30 cm (12 inches), hammer in a stake behind it for support. Attach the trunk of the seedling to the stake using a strip of cotton fabric.
Begin fertilising the laburnum seedling in the spring of the second year before blooming begins.
Apply a water-soluble fertiliser according to label directions. Fertilise every spring thereafter just before blooming.
Soil testing kits are available in hardware shops and garden centres.
Pressing one of your fingers down into the soil to a depth of 2.5 cm (1 inch) can help you determine whether the soil needs watering.
Don't forget to place the screening over the planted seeds. The screen will protect the seeds from hungry predators that may otherwise dig up the seeds.
A laburnum tree is poisonous, so keep it out of reach of pets and children.