Helping your plants in the big freeze

Snow covered cherub at Preston Bissett Nurseries
Snow covered cherub at Preston Bissett Nurseries

The cold arrives and sometimes it’s just a little bit too cold for some plants.

Often it is the combination of wet and severe cold that is damaging. This is usually worse in poorly drained heavy clay soils.

The joy of English gardens is the cosmopolitan variety of plants we grow - Japonicas from Japan, Orientalis from Asia.

It is not surprising some cope better with extremes than others and I find it helpful to know something of where plants originate.

It is easy to get a broom and knock the snow from the leaves of large leafy evergreens. Lots of snow on the leaves can cause cell damage appearing like scorch on even frost hardy plants.

Morning sun from the east can cause more damage when the frozen leaves are thawed too quickly and increase the chance of cell damage. Snow can also weigh down the branches and cause them to break. Plants in pots will be colder than the equivalent plants buried in the ground.

Stand them somewhere a little more sheltered from the weather for a few days or even pop some fleece on top.

Many plants find -10degC nights uncomfortable. I prefer to be a little more cautious as I do have rather a lot of plants to worry about!

These heavy cold spells seem to perpetually affect the same plants and as it warms up in March and the growing season begins the extent of damage will only then become apparent.

Bay plants will struggle if not already well established with a strong root system under the ground and a little shelter from the house.

Rosemary will hate the cold and young plants in wet positions will probably not survive. If they are in a drier soil and there’s not too much to freeze they may make it. Those in pots will be colder than those planted in the ground as the cold air can penetrate the pot. I have moved mine into the shelter of the eaves of my house and I hope this is enough.

None of the silvery Mediterranean herbs will love this weather - this includes sages and lavenders, and these don’t like to be over wet or sit in water.

Pittosporums and the contorted corokia can struggle. I think this is why they are best planted close to a warm wall. Watch the snow on the massive dinner plate leaves of the fatsias and knock it off if you can.

Choisya ternata always takes a hit from the cold. Often the juvenile shoots turn brown but usually they make a full recovery. When you consider they have originated from Mexico, Arizona way, I think they do pretty well to deal with our climate.

Agapanthus are bulbs that really dislike wet soggy cold conditions and when you remember they come largely from South Africa should we be in any way surprised!

Alpine plants are usually low growing, often good ground cover and great in cold but desperate for a well drained position resembling the alpine slope they used to call home. On the slopes lots of water passes through and drains away. Slopes often cover with snow but when a thaw occurred water would seep away through the rocky hillside.

Once plants are forced to sit in unhappily soggy conditions, planted in a flat border or a heavy soil or both, for any length of time they become susceptible to fugal diseases which are free to breed and usually rot the roots.

Californian plants speak for themselves. I used to have a prized wonderful ceanothus for about seven years and suddenly half of it died - I blame the snow of 2009.

When it tried to grow in the spring half the plant had turned brittle and brown. It may have been susceptible to botryosphaeria a fungal disease due to the cold soggy conditions or possibly its roots could no longer support its full size due to freezing cells in the freezing wet clay soil.

The combination of extreme cold combined with extreme wet conditions is quite a cruel challenge.

I would always plant warmer climate plants in the spring rather than autumn and give them a chance to establish before cold sets in and they do prefer to be sheltered by a warm wall or a thick shrubbery or fence. If you can improve the drainage with grit in heavy soils it would be beneficial except when we have drought like in 2011 and plants want all the moisture they can get!

How will we gardeners ever get it right!

Jacky Richardson, Preston Bissett Nurseries