When Do Alder Trees Bloom?

Alder trees are known for their distinctive flowers and seed cones, which are their top identifying features. With this in mind, you may be wondering: when do alder trees bloom? And what do their flowers look like? Keep reading as we answer these and other questions.

When Do Alder Trees Bloom?

When Do Alder Trees Bloom

Like most trees and plants, alders begin producing their blooms, known as catkins, when the weather warms up. The catkins appear in late winter through mid-spring depending on the weather and climate.

Generally speaking, alder trees bloom from February to April. But they may begin blooming later than that in colder regions.

In most alder species, the catkins appear before the leaves. An exception to the rule is the green alder, which develops leaves before it begins producing catkins a little later in the spring.

What Do Alder Tree Flowers Look Like?

Alder trees produce both male and female catkins on the same tree, and they are easy to tell apart from each other.

  • Male catkins are oblong and can grow more than two inches in length. They produce a fuzzy substance that blows on the wind and pollinates the female catkins.
  • Female catkins typically grow close to the male catkins on the tree, but they are shorter and rounder. Late in the season, they become brown and spread open like small pine cones to release their seeds.

The catkins may come in different colors depending on the variety of alder in question. The black alder, for example, produces yellowish male catkins, while its female catkins have a more purplish hue.

When the female catkins mature into strobiles (the cone-like structures), they remain on the tree throughout the winter, even after the leaves and male catkins have fallen. They provide a good source of food for many forms of wildlife that rely on alder seeds during the winter.

That said, most seeds are gradually released throughout the fall and winter months. As they fall, the lightweight seeds are carried away from their parent tree on the wind, widely dispersing themselves throughout the area. 

Can You Identify an Alder Tree By its Flowers?

As noted, alder flowers are fairly easy to identify; this is especially true of the female flowers. But can you use these flowers to identify an alder tree?

Alders are deciduous trees; they shed their leaves and some of their catkins in the fall and winter. But the female catkins, having matured into strobiles, remain on the tree.

The strobiles look a lot like tiny pine cones, giving alder trees character even during the dormant season. They are the only deciduous tree known to produce these cone-like structures.

With this in mind, you can easily use the strobiles to identify an alder tree, especially in winter. Look for a tree that is bare except for the clusters of tiny cones.

Most alders have yellowish male catkins. They are not as easily identified as female catkins, as they look quite similar to those produced by other trees–especially hazel, as noted in the following video:

That said, some species of alder have uniquely-colored male catkins, making them easier to identify. The gray alder, for example, produces reddish-colored male catkins. 

Regardless of the color of male catkins, the presence of female catkins on the same tree can help you correctly identify an alder tree even during the summer. The sight of both reproductive structures growing together on the same tree is unique and easily recognizable.

Do All Alder Trees Bloom?

The flowers on an alder tree are an essential part of the tree’s reproductive cycle. The catkins produce seeds, which allow the species as a whole to propagate and proliferate.

The color and appearance of the flowers varies slightly, but the overall process remains the same among all species of alder. All alder trees produce flowers in the form of male and female catkins. 

How Many Kinds of Alder Trees Are There?

Alder trees are a common sight in many parts of the world. They seem to prefer cool, damp climates in the Northern Hemisphere but can adapt to a variety of environmental conditions.

That said, not all types of alder trees grow in all parts of the tree’s range. Alder trees belong to the Aldus genus, which in turn belongs to the same family as birch trees; but there are quite a few variations of alder.

In fact, there are about 30 individual alder species in the world. They are identified based on their native habitat and physical differences, such as the differing appearances of catkins, bark color, and leaf color.


Alder trees typically bloom in late winter through mid-spring–most commonly between the months of February and April. They produce both male and female flowers, or catkins, on each tree, and they are wind-pollinated to ensure sufficient pollen and seed dispersal.

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