Nature on our doorsteps: Fighting the frosts . . .

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into nature on our doorsteps and the beautiful biodiversity of its plants and wildlife.

The first frost has been late this year, appearing only at the end of November.

Frost will only form under particular weather conditions.

Clouds act like a blanket above the earth, keeping in the heat which normally rises from the land. If wind is present, this also mixes up the air between the ground the blanket of cloud, creating a uniform temperature within the column of air.

Frost, however, needs different conditions before it can form. On a cold cloudless night, when there is no wind, the heat rising from the earth can drift all the way up into the higher atmosphere.

As the heat rises, it pushes the heavier colder air of the upper atmosphere down towards the ground. This colder air rolls down into valleys and across flat ground and can form ‘pockets’ of frost.

When pond surface freezes, water creatures move down into the mud at the bottom

Ground frosts occur when the temperature of the ground falls below freezing point (0° Celsius), while air frost occurs when the temperature of the air falls below freezing point.

Native plants are generally adapted to survive short periods of frosty conditions. Longer periods can still do damage, however.

Many well-loved garden plants are not native to Ireland, and gardeners try to protect these from the effects of frost.

Frost acts by freezing the water that is present in and between plant cells.

As this water freezes it expands, causing it to burst through the cell’s walls. When the frozen water eventually melts, the contents of the cell leak away, and the area affected will die off.

To prevent such damage, trees prepare for frosty winter weather by discarding their soft leaves in autumn.

The tree first withdraws all the nutrients from the leaves and stores this deep in their woody parts, away from cold conditions.

Trees can also produce a substance in their cells which acts very much like an anti-freeze, preventing any water in their woody cells from freezing.