It’s typical of New Zealand weather to hold back the worst until last, and this season is no exception. While early winter was mild in many places (my neighbour reported he was still mowing his lawns into July!) snow and chilling frosts have struck in both main islands. When freezing conditions and icy blasts hit one on top of the other, or at unexpected times of the year, or in the most unlikely places, it’s important to know what you’re doing to protect your plants.
Frost damage is easy to spot. Leaves become limp and often turn black, and the foliage of evergreens gets a worryingly ‘translucent’ look about it. Some of the worst frost affected plants are those that are north facing. As the first sun of the morning reaches them, it causes their growth to defrost too quickly and bursts the walls of the cells in their leaves. If you’re receiving frosts where you once didn’t, or frosts that are heavier than usual, it may pay to think long-term. Whether or not you’re a climate change sceptic, seasons are changing and we can expect more severe weather events from here in. If you favour gold or variegated plants, it may pay to pick another favourite as these colourful specimens are often more tender than their plain green cousins.
If you’re heavy handed with the nitrogen, change your ways or at least avoid scattering it early or late in the growing season. Nitrogen fertilizers cause plants to put on extra leaf growth and any tender new foliage will quickly be destroyed by very cold conditions.
Even if you already plant half-hardies in sheltered spots, you may want to consider covering them with horticultural fleece during cold spells. This product allows the sun in, along with air circulation, but helps keep the cold out. An old method of plant protection, which I learned from more experienced gardeners early on in my gardening ‘career’, and at a time when such luxuries as fleece and plastic wrap were not available, is to delay cutting back autumn foliage. The spent, brown seed heads and dead foliage of many plants shut out the frost and snow from their base and protect crowns and new growth from the cold. In a similar fashion, a thick layer of mulch on the ground will also protect hibernating plants.
While ice and snow are the more obvious enemies in the garden in winter, endless rain can also wreck havoc, drowning low lying or damp-sensitive plants and bulbs. Shut out the worst of the wet by covering these plants with a ready-made cloche of clear plastic or a few panes of old glass held aloft on a base of bricks. Where possible, plant water-sensitive treasures on small hillocks or a slope, and incorporate stone chip into the soil to assist with drainage.
Where plants have already copped winter damage, a rescue remedy should be employed. Wait until spring to cut back frosted growth to a new bud (the damaged foliage is at least helping protect the remaining growth from the cold) and, once winter has passed, feed your plants to encourage new spring growth to come away quickly. If frost bites north facing plants, cover them with black plastic in the early morning so they have time to defrost gradually. Check plants for ‘frost heave’, a situation where the expansion of frozen water in the soil lifts the plants partially out of the ground. Firm them back in as soon as possible, and if freezing conditions continue and make this impossible, temporarily cover any exposed roots with mulch.
In severe weather conditions, it’s a case of not giving in but carrying on. And one thing is certain (at least for the time being): spring is just around the corner.