Every October, the Japanese maples (Acer palmatum) in my collection put on a show that stops visitors in their tracks. After 40 years of growing plants, it still fascinates me. Here is what is actually happening inside those leaves.

Step 1: The green fades
All summer, leaves are packed with chlorophyll, the green pigment that turns sunlight into energy. As the days shorten and nights cool, the tree stops making new chlorophyll and starts pulling valuable nutrients, such as nitrogen, back into its branches for winter. As the green disappears, the yellow and orange pigments (carotenoids) that were there all along finally show through.

Step 2: The red is brand new
Red is a different story. The red and purple tones come from anthocyanins, pigments the leaf makes fresh in autumn from the sugars still trapped in it. This is why the colour can be so intense: it is not left over, it is produced on purpose.

What makes the red stronger?

• Sunny days: bright light helps the leaf produce lots of sugar and drives anthocyanin production.
• Cool nights (above freezing): the sugars stay in the leaf instead of moving out.
• A dry, sunny autumn: this usually gives better colour than a warm, rainy one.
• A hard early frost: this can end the show early and drop the leaves before they reach full colour.
• Genetics: some varieties are bred for fiery autumn red, and others keep red or purple leaves all season.

Why do trees do it?
Scientists haven’t fully agreed on this. One theory is that anthocyanins work like sunscreen, protecting the leaf while the tree recovers its nutrients. Another is that they help deter insects. Either way, the colour has a purpose.

Getting great autumn colour in your own garden

• Light: choose a bright spot, ideally with some shade from the strongest midday and afternoon sun.
• Shelter: protect the plant from strong, drying wind.
• Soil: use well-drained, slightly acidic soil that never dries out completely or sits waterlogged.
• Watering: water during long dry spells, especially in summer and early autumn.
• Pots: in containers, protect the roots from hard frost in winter.

Every maple is unique, and the colour changes a little from year to year with the weather. That’s part of the charm.

Looking for a maple for your own garden or terrace? Have a look at our current ACER selection.