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20 May 2022

During winter, frosts occur on clear, still nights. As the air outdoors gets closer to freezing (0o C), the surface temperature of your plants can go below freezing causing ice crystals to form, just as dew forms on warm nights. Of course, temperatures vary just above ground level so frost can also form even when the thermometer isn’t at 0o C.

Wherever your live in NZ your plant might continue to grow throughout the winter, even if it's slower. If the plant is in a pot, make sure it’s not rootbound. If there are roots coming out the bottom it is time to find a larger pot, and you can feed the plant well at the same time.

If you have a swan plant in your garden that you want to protect for next season, and during previous winters you’ve experienced frosts, snow and freezing conditions, you might find these tips helpful.

  • Prune your plants

Cut off any old growth, dead stems, discoloured leaves. When you cut the stem, cut on an angle away from the ground so that any moisture is more likely to drain away, rather than sit on the open wound. Also make the cut just above a node, where the buds are located.



This area has great cellular activity and growth. New buds will form in the spring and develop into stems with more leaves. Each cut is going to provide twice the amount of growth. You should be able to feed twice as many caterpillars!

  • Cover your plants

Almost any type of covering will work, but old blankets, sheets, and even burlap sacks are best. Drape the covering loosely and use stakes, ties, rocks, or bricks to keep it in place. Plants growing under the eaves of your house and on the northern side (usually more sheltered and getting more sun) already have the advantage. You’ll have to put some thought into placing the covering … you don’t want to squash your plant, but the pruning will have helped eliminate the weaker stems. Spring-loaded clothes pegs are really handy. Put the covers over in the evening and that will keep in any heat from the day, and remove the covers when the sun comes out the next morning. You don’t want your plant to suffocate.

  • Mulch your plants

Mulch helps to lock in moisture and, during cold weather, holds in heat. Try to keep it thick, about 5-10 cm is ideal. You can use loosely-piled leaves, straw, pine needles, bark or shredded paper.

  • Water your plants

If you have a good warning system that a frost is on the way, water the plants well before frosty weather arrives. Wet soil holds more heat than dry soil – but don’t saturate your plants while temperatures are low as this could cause the soil to swell when it freezes.

  •  Cold frames

If you see seedlings in your garden, you could pot these up and put them in a cold frame. Cold frames can easily be made from old windows and bricks – basically they are four walls with a glass ‘ceiling’. I have seen a cold frame made with old hay bales which are great insulation. A great opportunity to recycle old materials.

We hope these tips are helpful to those of you living in colder climes. Some of our members in Dunedin manage to overwinter their plants … so perhaps you can do so too (even if people say you can’t).

2 comments on “Frosts”

  1. I've seen a few Monarchs recently, and have at least 2 cats on my quite young plants, so should I tell them the `season' is over????!! Or perhaps bring them indoors as I have done before? On cuttings in Gingerbeer bottles!!

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