To keep with the Halloween theme, here’s Arlena’s
image of her succulent stuffed pumpkin.
There are a couple of pointers to remind me of the oncoming cooler
weather. Two being the shorter days and the ever decreasing times that I can
take my dogs for a walk in the daylight around the park. Then there’s the
butter dish on the kitchen table. Gone are the days when I can scrape out big dollops
of lovely creamy butter onto my knife. It’s now a case of placing lumps on the
toast and letting it soften. We are slowly being acclimatised to the colder
weather so when the first frost comes it’s not too much of a shock to the
system. Plants also acclimatise themselves, not by putting the butter in the
microwave, but by changing their metabolism, anatomy and physiology to prevent
frost or chill damage.
How do plants cope?
One response plants have to dropping temperatures is the
thickening of liquid within plant cell membranes, from a liquid to a gel-like
state with amino acids. This slows everything down, conserves energy and lowers
the freezing point, a bit like antifreeze. At the same time, the cell membranes
themselves become more permeable, allowing water to leak between the cells as a
kind of buffer. This is the process of cold acclimation.
Acclimatisation is also known as ‘superfreeze’ where the
cell contents remain liquid even though below freezing point. To do this plants
have to experience several days of cold weather before the freeze and this
explains why even hardy plants can be damaged by a sudden autumn frost.
2 Types of Frost
The two main types of frost are advective or radiative,
depending on the atmospheric conditions. An advective frost occurs when cold
air sweeps in, usually with strong winds. A radiative frost occurs on clear
nights where there is little or no wind.
Frost can Benefit Plants
Frost can actually benefit some plants. Deciduous fruit
trees benefit from winter chilling, and cold snaps turn starches to sugar in
crops such as parsnips, improving their flavour.
Frosts can also disrupt pest and disease cycles, and improve
soil structure – when moisture within soil freezes, it expands, and splits open
soil particles.
Prevention of damage
There are a number of ways to keep your plants safe during
cold weather;
Choose plants that are reliably hardy and suited to your
growing conditions.
Select planting positions carefully to avoid ‘frost pockets’
this usually happens at the low point of the garden.
Slightly tender plants should be grown in a warm sunny spot,
against a south-facing wall for example, which will provide some extra warmth
and winter protection.
Cover plants with a double layer of horticultural fleece or
other suitable protection when frost is forecast. This cover is thin enough to
let sunlight in, warming the soil and to keep in the warmth at night as the
temperature drops.
Mulch the root area of evergreens now, conifers, tender
shrubs and tender perennials with a thick layer of organic matter to prevent
the ground becoming frozen. This is better done in warmer weather as adding
mulch later on could trap the cold air in the ground.
Move container-grown plants to a sheltered part of the
garden in cold weather and provide some extra protection by wrapping the pot in
bubble wrap.
Leave the previous seasons growth on more tender plants
until spring, for example penstemon, as this provides valuable frost protection
during the winter.
Tender plants can be lifted or moved to a more sheltered
position or greenhouse. If this is not practical then protect them by wrapping
them in sacking.
Lift tender perennials such as dahlias, cannas, pelargoniums
and fuchsias before the first frosts.
Hardiness can be improved by feeding plants high
concentrations of soluble nutrients including potassium and sugars in the
growing season. Some plants also have physical protection such as thick bark,
furry leaves or a canopy that protects the inner shoots. Avoid applying
nitrogen-rich fertilisers late in the season though as they stimulate soft,
sappy growth which is especially vulnerable to frost damage.
Plants exposed to early morning sun may thaw too rapidly
after a frost, causing damage to flowers and young growth. Camellia and
magnolia flowers in particular can be ruined by a single frost.
Ensure tender plants are overwintered safely in the
greenhouse by providing adequate heating or insulation
It's the late frosts that we should be the most wary of. Plants
emerge gradually from dormancy in spring, but they can still respond quickly to
sudden spikes in temperature which triggers new fresh growth which is very
vulnerable to cold snaps. It’ll be a while before we need to give that any
thought though!
