Question 1

Why did my hydrangea change colour?

Accepted Answer

Because the colour of a mophead or lacecap hydrangea is set by soil chemistry rather than by the variety alone, and something about your soil has shifted.

The mechanism is aluminium. Blue pigment forms when aluminium ions are taken up by the plant and bind to the pigment molecules in the flower. Aluminium is present in most soils but is only soluble enough for roots to absorb it when the soil is acidic — below roughly pH 5.5. In alkaline soil the aluminium locks up in forms the plant cannot use, and the same flowers come out pink. Between those extremes you get muddled purples and blues and pinks on the same shrub.

So a plant that was blue in the nursery pot and turned pink in your garden has not changed variety. It was grown in an acidic, aluminium-rich compost and has now been planted in more alkaline ground. The reverse happens too, particularly where rainwater from a limestone roof or mortar leaching from a nearby wall raises the pH over time.

Two important limits. White hydrangeas have no pigment to shift and stay white regardless of soil. And paniculata and quercifolia types do not respond to pH at all — only the macrophylla group does.

Changing colour deliberately is slow and partial. To push toward blue, lower the pH with ericaceous compost, sulphur chips or a proprietary hydrangea colourant containing aluminium sulphate, applied over a full season. To push toward pink, add garden lime. Growing in a container gives far more control than trying to alter open ground, where the surrounding soil constantly re-asserts itself.

Question 2

What is ericaceous compost and which plants need it?

Accepted Answer

Ericaceous compost is a growing medium formulated to be acidic, typically around pH 4 to 5, for plants that cannot take up nutrients properly in neutral or alkaline conditions. Soil pH does not

Question 3

Why are my plant's leaves turning yellow?

Accepted Answer

Yellowing is a general stress response rather than a specific diagnosis, so the pattern matters more than the colour. Which leaves yellow, and how, narrows the cause considerably. Overwatering is the

Question 4

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 5

How do you test your soil, and does pH actually matter?

Accepted Answer

With a simple kit or a laboratory test — and pH matters enormously, not because plants care about acidity directly, but because it controls which nutrients are available to be taken up at all. Why pH

Question 6

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

Question 7

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

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