Laburnum alpinum

Description

Scotch laburnum

One of the best flowering trees for cold temperate climates, Laburnum alpinum is a fast-growing but short-lived, deciduous small tree or large shrub to 5 m tall with tripartite leaves and masses of long, pendulous racemes of bright yellow, sweetly scented flowers. It is native to central and southeastern Europe. All parts of the plant are toxic to humans and some other mammals.

Seeds have a very hard, water-impermeable seed coat and require pretreatment for successful germination to occur. Without pretreatment, it is likely that 10% or less of the seeds will germinate. The first (and easiest) method is to place the seeds in a heat-proof container and pour hot (not boiling!) water 70-80 degrees Celsius over them and leave them to soak for between 12-24 hours. Seeds that have been successfully pretreated will have swollen to around 3 times their previous size. Remove all swollen seeds as these will be damaged by further pretreatments. These can be sown immediately. This hot water treatment can be repeated up to 3 times, making the water a little hotter each time. The remaining method is to physically break through the seed coat by cutting or (k)nicking the edge of the seed with a knife or using a file or even rubbing them between layers of fine sandpaper. The seeds are very long-lived and can remain viable in the field for 30 years. Sow in pots or seed trays of good quality compost at a depth of about 2cm (just less than 1 inch) The seed usually germinates in under 4 weeks at 15-20°c. Growth in the first year is modest, usually between 20 and 40cm. Plant trees out into their permanent positions after 2 or 3 years of growth.