It’s spring, and the weeping branches of willow trees are beginning to burst into life with nectar-rich catkins and buzzing pollinators.
There are over 14 native species of willow in the UK, including Salix caprea (goat willow), Salix alba (white willow), and Salix cinerea (grey Willow). Although their flowers not as showy as other spring blooms, they are equally as important for our local ecosystems β and incredibly interesting! In this post, we’ll explore what willow flowers look like, when they bloom, how they’re pollinated, and more.
Do willow trees flower?
Yes, willow trees produce flowers! They have long, caterpillar-like blooms known as catkins, which are made of many tiny petalless flowers.
Willow trees are dioecious species, meaning they have separate male and female trees (although there are some exceptions). The appearance and function of their flowers will differ depending on whether the tree you are looking at is male or female.
Male vs female willow flowers
Male willow tree flowers
Male willow tree catkins begin as greyish, furry buds, which slowly elongate and become a light shade of green as they grow. Once mature, their stamens (the narrow, hair-like filaments) have yellow pollen-laden tips. They also produce nectar to attract pollinators. Male willow trees cannot produce seeds.
Female willow tree flowers
Female willow tree catkins are made up of lots of small, green pistillate (female) flowers. Each pistil is teardrop or cone-shaped with a ruffled or v-shaped tip. Often, they have a soft, downy feel. Like their male counterparts, they contain nectar to attract pollinators. When fertilised by pollen from a male willow tree, the female flowers will develop seeds.
Male willow flowers sometimes look quite similar to female flowers β especially when they’ve lost their grey fuzz but aren’t mature enough to have pollen on show yet. I recommend looking at as many flowers as you can find on the tree because you’ll be able to find catkins at different stages of development.
Bud scales on willow trees
You may notice a woody shell where willow tree flowers join the branch of the tree. This shell is a modified leaf called a bud scale, which protects the flower buds (and developing leaves) during winter to prevent water loss and damage to their tissues from the cold.
Variations between species
Visual differences between catkins
There are many species of willow (as well as hybrids), and there are subtle differences between their catkins. White willow catkins, for example, are long and a greenish yellow, while Goat willow catkins are short, fuzzy, and often grey.
Monoecious willows
Although most willow species are are dioecious, there are some which are monoecious (individual trees which produce both male and female flowers). One such example is the Golden Weeping Willow, which is a hybrid between the white willow (Salix alba) and Babylon weeping willow (Salix babylonica). As a result of having both male and female flowers, the golden weeping willow is capable of fertilising its own flowers.
When do willow trees bloom?
Willow trees tend to bloom at the beginning of spring, between April and May. The mild temperatures but windy conditions are ideal for willow flowers, which are adapted for wind pollination. Some varieties, such as the Goat willow, have a layer of hair-like fuzz that helps insulate them from colder weather so they can produce flowers as early as late February.
They are considered to be hysteranthous plants, meaning that they flower before their leaves emerge. This adaptation helps them disperse their pollen more effectively.
How are willow trees pollinated?
Wind pollination
Willow trees are adapted for wind pollination, similar to many other early spring flowers (such as oak and birch). The long, garland-like shape of their catkins helps them move freely, dispersing pollen when wind blows through the tree. Willow pollen is very light, allowing it to be carried easily through the air to reach female flowers.
Insect pollination
They are also pollinated by insects. While foraging, some of these creatures may transfer male pollen to a female flower, allowing fertilisation to occur. During the early spring, the nectar and pollen from willow flowers are important food sources for more than 500 species of native UK insects. Some of the wildlife you might see feasting on the nectar and pollen from their flowers include bees, butterflies, wasps, moths, hoverflies, and more.
Willow tree flowers and bees
Willow tree flowers provide food for solitary and social bees during the early spring. A Canadian study of bee foraging preferences on willow trees showed that male flowers β which have both pollen and nectar β were strongly favoured by bees over female flowers.
Willow tree flowers and birds
The insects that are attracted to willow catkins can draw birds to these trees to forage. There are even some reports of blue tits feeding on the nectar of grey and goat willow catkins.
Additionally, certain species of willow catkins, like those from the goat willow, are sometimes used by birds as nesting material. With a light and fluffy texture, they’re ideal for creating a soft and comfortable nesting surface.
Do willow trees produce seeds?
Yes, willow trees produce seeds. The flowers of a female tree will form seeds after successful cross-pollination from a male tree. Willow seeds germinate rapidly because they don’t have an endosperm (tissue that provides nourishment and regulates dormancy), which means that they have a short shelf life.
Similarly to how willow flowers are adapted for wind pollination, their seeds are designed to be carried by the wind or water. While the seeds themselves are small and light, they have a fluffy, cotton-like down that can help them travel long distances.
Propagation
Willows also self-propagate. They have high concentrations of Indolebutyric acid (rooting hormones) in the tips of their branches. This hormone allows stems that are severed from the main plant to easily take root and become new trees.
In most garden centres, you won’t be able to find willow tree seeds for sale. Taking cuttings is far easier than trying to harvest and store the delicate seeds they produce!
Did you know?
A single willow tree stem is known as a withy or withe. Living withes can be used for propagation, while partially dried and re-soaked withes are ideal for basket weaving and other crafts.
When do willow trees seed?
Most willow trees in the UK will seed in late May or early June. The seeds are quickly carried away by the wind, so it’s a very fleeting (but beautiful) display β well worth keeping an eye out for! Additionally, if you’re trying to figure out whether a tree is male or female, this can be a helpful time to do so, as only females will produce seeds.
Overall, willow catkins play an important role in the reproduction of these trees, allowing them to produce seeds that can travel to much further distances than self-propagated branches. They also provide a vital source of food for local wildlife during the early spring, helping to support many of the pollinators we depend on. I hope you found this post helpful and perhaps learnt something new about willow catkins!
This post was all about willow flowers/ catkins.
