A cool climate winter has a certain charm, with clear sunny days and blue skies to highlight plant silhouettes. Winter flowers and vegetables are valued too, but frosty nights can take their toll. Exposed areas in new suburbs are particularly susceptible, where larger plantings have not been established long enough to create a micro-climate that will offer a certain amount of shelter.
There are known degrees of plant hardiness, though perhaps what is not so well known is that there are degrees of hardiness between varieties in the same species. Local nurserymen will have knowledge of which will do best on your planned planting site.
Hollows at the base of sloping ground become frost pockets in exposed conditions, and the temperature that a plant experiences and can cope with would be decidedly lower than if it were planted further up the slope.
Soil drainage in particular has a bearing on even the most frost hardy plants. One that might normally cope with up to 10 degrees of frost may well succumb at -2C if the roots remain constantly wet. Borderline plants will survive many degrees of cold when planted into well drained ground, especially where they can benefit from the sun’s warmth radiated from house walls.
Cultural methods after the first 12 months can assist minimally hardy plants to withstand lower temperatures. If you gradually reduce the amount of water (but ensuring it goes directly to the plant roots), together with an autumn feed which includes potash, a stronger celled, more winter-hardy plant will be the result.
One simple method of frost protection of tender shrubs like lemon trees is with the use of a hessian cover draped over four stakes but make sure top is higher than any foliage that can still be damaged where touched. Herbs such as parsley and oregano will survive under polythene covers, though they should be removed during the day to avoid over-heating.
Frosts occur on cloudless nights when clear sky means that heat is rapidly lost from both soil and plant tissue. Should you be unfortunate enough to find frozen foliage on favourite pot plants, spray a fine mist over them before the sun strikes. This should gradually melt any ice that has formed and help the plants survive the damaging period of thaw.
In severe frosts, soil particles can be pushed apart by expanding ice which results in the roots of some plants – particularly the shallow rooted kinds – being snapped off, causing the plant to ‘lift’ out of the ground.