Fresh spring green: everything you want to know about tree leaf flush

Are you also enjoying the spring sun? Nature is exploding! Due to the early arrival of spring and the sunny weather recently, we can welcome our deciduous species back to our range extra early this year! You can now buy the birch, ginkgo, albizia and bee tree again at Bloompost and Plantje.nl. The start of the growing season is a good time to tell you more about the phenomenon of 'leaf flush' or 'leaf out' and why each deciduous species has its own 'planning'.

What is leaf out or leaf flush?

If there's one thing we know for sure, it's that nature sprouts in the spring. For hundreds of millions of years, temperate latitudes have had a seasonal cycle in which spring marks the start of the new growing season. Seeds germinate, buds open and leaves stretch toward the light. Within a few weeks, everything will be fresh green again. But what makes this lightning-fast metamorphosis possible?

The secret for trees lies in the buds: they are already on the tree before the leaves fall in autumn! The leaves and often also the flowers of trees have already been on a tree all winter, just safely stored in a bud. Everything a tree needs to form a new leaf or flower is in there. You can clearly see this when looking at the cross section of a chestnut bud below. Even the flower is recognisable. As soon as the conditions are right, this protective layer can be removed, and the leaves and flowers show themselves. The process is actually the same as with flower bulbs, because you also put them in the ground before the winter.

When do trees leaf out?

Exactly when a tree sprouts depends on several factors such as location, day length and outside temperature. For example, trees in a warm and sunny spot, such as a south-facing slope, are more likely to sprout than individuals of the same species in a cooler, shady spot. Since trees need their leaves to harvest solar energy, you might expect them all to shoot out their leaves at the first rays of sunshine and heat. But this is not always the best strategy. For most species it is a complex interplay of all the aforementioned factors and it is not so easy to pinpoint a specific reason for sprouting.

Some trees, such as the birch, start producing new leaves early: as soon as there are a minimum number of days when the ambient temperature is higher than a specific temperature. This is a risky strategy, as temperatures can fall well below freezing this early in the spring, causing the new leaves to freeze to pieces. Other tree species take less risk and wait until the chance of frost is less prominent. Most do this on the basis of a required number of cold days in winter, often in combination with a certain number of hours of sunshine in a day. The downside is that the competition has already taken a lead in the battle for light and nutrients.

The latter is no problem for a tree in a pot. You can place it in a sheltered and warm spot in the house or in the garden. Did you get a Treemore tree in the winter or early spring? Keep it indoors for a while or put the tree in a sheltered spot during night frost.

The evolutionary history of the tree species also influences: if it originated in a warmer climate, such as the albizia, it most likely has less fully adapted mechanisms for dealing with extreme cold and may therefore have different factors regulating leaf shedding than a tree species native to the Northern Hemisphere.

Colourful spring

You may have noticed that the new leaves of trees and plants often have a different color. Young leaves often have less chlorophyll, which means that the new leaves are often lighter in color than the fully grown leaves. This difference is also clearly visible in coniferous trees. The new needles are much lighter green than last year's. We also see this nicely in our trees. The new foliage is light in color and gives that fresh spring feeling.

In most trees the new leaf is light green, but the color of new leaves can also be white or red. In the tropics, it is more common for a tree's new leaves to be reddish rather than light green. The reason for this is most likely due to the presence of specific pigments, especially anthocyanins, which cause this color and provide protection against insects and fungi.

Spring is therefore not only colourful because everything starts to bloom, but also because of the diversity of colours in new leaves. Now that you know all about those new leaves, you might be excited to see this up close for yourself. This is possible with our range of deciduous trees, whose 1-year-old seedlings are now busy sprouting. Or, put a loved one in the spring sun and give a letterbox tree as a gift!