25-Mar London’s Willow and Poplar Magic

Willows are trees with separate sexes and a phenomenal ability to hybridise. Consequently, yet again it is not easy to identify the trees you encounter. The goat willow, pussy willow and common willow are all names for the same plant, Salix caprea, which is the most common and easily identified willow you are likely to see on waste ground. Its silvery catkins so typical of the beginning of the month develop into the bright yellow male pussy willow catkins or into the familiar long green female catkins. When pollen and nectar are being produced at this ‘yellow stage’, these trees stand out wherever they are. They are very attractive food sources for early insects and consequently attract the early insect-eating migrant birds.

Good places to see them are railway embankments. The other willows likely to be noticed but not for their catkins, are various weeping willows and crack willows S. fragilis. Weeping willows are planted in gardens all over London for their attractive weeping foliage and crack willows are common around our lakes and ponds. Both produce small, green catkins this month but are noteworthy for the intense shade of green of their unfolding leaves.

The other common tree now with bright green leaves is the hawthorn. Various species and cultivars of both willows and hawthorns provide much of the green colour in the first half of the month. There are probably in the region of thirty different willows existing in a semi-wild state in London and this is excluding the numerous different hybrids.

On top of these, there are many more rare willows in our gardens. The contorted willow S. masuda’s Koidzuma ‘Tortuosa’ is one of the most popular due to the curves on its branches every three centimetres. Other small weeping forms with cascades of silvery catkins have become popular in recent years e.g. S. caprea ‘Kilmarnock’. To the general observer, the other characteristic of willows that stands out is the colour or ‘bloom’ on their twigs. This can vary from green, yellow, orange and red through to violet with some changing their colour as spring advances. The catkins of the goat willow are quickly followed by those of the grey willow S. cinerea which has similar but slightly larger catkins.

Then comes the rarer violet willow S. acutifolia, the purple willow S. purpurea and common osier S. viminalis. The last one has much longer leaves and is nearly always found at the edge of waterways. Kew Gardens has a good collection of named species, including S. aegyiptiaca and S. alba x fragile and Chelsea Physic garden is also worth visiting for Salix x rubens ‘Barfordiana’ and S. gracilistyla melanostachys.

Poplars, like willows, are single sexed and they also hybridise freely. The white poplar Populus alba, grey poplar P. canescens and aspen P. tremula all do well in London, reproducing successfully by suckers. A rare weeping aspen Populus tremula ‘pendula’ with leaves that don’t tremble like other aspens can be found in Cannizaro Park.

Lombardy poplars P. nigra ‘italica’ are also common around London and are nearly all male. Towards the end of the month they will all be decorated in crimson catkins. White poplars and aspens are both producing small, greenish catkins, grey poplars grey furry ones and those of balsam poplars are large and lemon-coloured.

Marcel Proust said the scent of riverside poplars reminded him of “the lost paradise of his infancy”. These are likely to have been Black poplars whose buds are known to have a pleasant scent.