Question 1

Why do leaves change colour in autumn?

Accepted Answer

Because the tree **withdraws** its most valuable resources before discarding the leaves — and the colours reveal what was there all along, plus something newly made.

**The green is chlorophyll**, the pigment that captures light for photosynthesis. It dominates all summer, masking everything else in the leaf.

**Why the tree sheds leaves at all.** Broadleaf leaves are thin and full of water, so they are destroyed by frost and lose water faster than frozen ground can supply it. In winter, a leaf costs more than it earns. Shedding is a controlled withdrawal, not a failure.

**The sequence, triggered mainly by shortening day length** rather than by temperature — which is why the timing is fairly consistent year to year:

**Chlorophyll production stops** and existing chlorophyll breaks down. Crucially, the tree **reabsorbs the nitrogen and magnesium** it contains — these are expensive nutrients, and recovering them is the point of the whole process.

**Yellows and oranges are revealed.** **Carotenoids** and **xanthophylls** were present all summer, doing accessory light capture and protecting against light damage. They simply become visible as the green goes. Birch, hazel and field maple are dominated by these.

**Reds are newly made.** **Anthocyanins** are **synthesised during autumn**, not revealed — which is why red colour varies enormously between years while yellow is consistent.

Why a tree would invest in making pigment in a leaf it is discarding is genuinely debated. Leading hypotheses: protecting the leaf from **light damage** while nutrients are withdrawn, since sunny cold days are exactly when the breakdown machinery is most vulnerable; and possibly deterring insects.

**Best red displays follow** warm sunny days and cool but frost-free nights, which favour sugar accumulation and anthocyanin production. A warm wet autumn gives dull colour; an early hard frost cuts it short.

**Browns** are tannins, what remains once everything else has gone.

**Abscission** finally seals and severs the leaf.

Question 2

What is dormancy, and why do plants die back?

Accepted Answer

Dormancy is an active, regulated shutdown rather than a passive response to cold — plants prepare for it in advance, and understanding that explains a great deal of seasonal gardening advice. How a

Question 3

Why do plants flower when they do?

Accepted Answer

Mostly because of day length, which is the only environmental signal reliable enough to time a life cycle by — temperature varies wildly from year to year, but the length of the night on a given date

Question 4

Why does my fruit tree crop heavily one year and not the next?

Accepted Answer

It is biennial bearing — a self-reinforcing cycle in which a heavy crop in one year prevents flower bud formation for the next, producing alternating years of glut and almost nothing. The mechanism.

Question 5

Do grow lights work, and does the colour matter?

Accepted Answer

They work, and the colour matters less than the intensity and duration — which is the reverse of what most marketing implies. What plants actually use. Photosynthesis is driven mainly by light in the

Question 6

Why has my variegated plant turned all green?

Accepted Answer

It has reverted — produced growth without the variegation — and if it is not removed it will take over the plant entirely, because the green growth has a genuine advantage. Why variegation exists.

Question 7

How do plants actually drink, and why does a plant wilt?

Accepted Answer

Water is not pumped — it is pulled up the plant by evaporation from the leaves, and wilting is what happens when that pull outruns the supply. The mechanism, working from the top down: Transpiration.

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