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Frost fight

3 May 2022

The race is on to protect our favourite heat-loving plants from winter’s chill. Words Diana Noonan

High-altitude temperatures are already dipping to zero overnight, and southern regions won’t be far behind. In warmer parts of the country, the chill is just a few weeks away. So it’s time to consider the different ways you can get set to protect and pamper your plants and keep them warm through winter. Whether it’s with the help of a greenhouse or a cloche, don’t let the cold months stop you growing!

Shifting home

Plants in pots are mobile, and most can be moved to more protected sites over winter – but watch your back with the heavier ones. To lighten the load in the future, plants with relatively shallow root systems can be grown in pots that have been half-filled with pieces of polystyrene or upended plastic plant pots before the growing mix is piled in on top.

Winter homes for non-hardy potted plants can include anywhere that is sheltered from frost, strong winds and heavy rain. Under the eaves of the house (especially the sunny side) works well. If the house has concrete or brick foundations, all the better as this material will heat up during the day and radiate the warmth back at night. The overhanging branches of trees can provide protection against frost, as do nooks at the base of evergreen hedges.

Going up

If you’re lucky enough to own a greenhouse, your moveable plants can be housed under-cover for the
winter. To maximise space, use multilayered shelving. While plants require stepped shelving during the
active growing season in order to have equal access to light, in the winter months this isn’t so necessary so you can build your own. Use bricks and wide planks to create shelves, or even old bookcases sourced from the recycling centre – but whatever you decide on, be sure to anchor it firmly in place to avoid it toppling and damaging the greenhouse.

Adding layers

Although greenhouses are usually five degrees warmer inside than outside temperatures, in very cold
parts of the country they are unlikely to be sufficient to avoid frost damaging plants. That’s where frost
cloth comes into its own. Drape it loosely over plants (using two or three layers if necessary, each loosely
placed over the other in order to trap air). To further protect plants, make sure they are not overwatered.
Root systems require very little moisture in the winter months, and plants that are growing in wet soil have a much greater chance of freezing than those kept relatively dry. Plants will survive under a layer of frost cloth all winter, but if you are using several layers, remove the material during the day so the plants
don’t become starved of light.

Snuggling down

Plants growing in the ground have their own form of protection. Some shrubs and trees drop their leaves and go into a state of dormancy, but other more fleshy plants retreat underground, leaving their spent, dry foliage on top to protect the living plant material just below the surface. In very cold regions, however, or if you are a fastidiously tidy gardener and have cleared away dead foliage from the garden
over autumn, you will have to help these dormant plants snuggle down.

To do this, pile 3–4cm of weed-free compost, pine needles or leaf litter over the plants. Check it regularly in case birds, rabbits or high winds scatter this protection. In late winter, if there have been bursts of warm weather, this mounding may need to take place a second time to protect new growth that is prematurely coming through the ground. In areas of high winter rainfall, a light mulch, such as pea straw, is the best cover to use as it won’t hold in moisture that could contribute to freezing.

Closing in

Not everyone has a greenhouse, but we can all aspire to growing fresh greens over winter by constructing cloches that don’t cost a fortune. In the edible garden, rows of vegetables can be covered with salvaged or purpose-bought plastic or horticultural fleece. In situations like this, bend supple willow, number 8 wire or polythene pipe to form an arch, pushing the ends of whatever you are using well into the ground to hold it in place. Cover with your chosen material, which can be gathered at each end, tied together and
weighed down with a rock or stone placed over the ‘tail’ of the fabric. If you are in a very windy region, cover your cloche with garden netting (such as bird or strawberry netting) and peg it into the ground along the side of the cloche.

Using plastic to cover your plants allows the sun to penetrate the cloche during the day while protecting the plants beneath from damaging temperatures and cold winds. But on very warm days, even in
winter, plants can still ‘cook’ in the heat.

Along with horticultural fleece, plastic also prevents moisture reaching the soil. A preferred material is ‘knitted polyethylene frost cloth’. It is available under several brand names, and because it is permeable to both air and water, overheating and unwanted humidity is prevented. There is also no danger of condensation building up and then dripping back down onto plants, exposing them to the risk of fungal invasion. Like all horticultural cloth, it will also protect your garden from domestic animals, birds, rabbits and possums.

Wrapping up

Larger plants that are too big for a cloche and too tender to survive the winter without protection can be ‘wrapped’ for the coldest months. This is a useful technique whether you live at high altitudes with severe frosts and snow or in warm regions where tender subtropicals are at risk from dipping temperatures.

Horticultural fleece is best used as a wrap if the material is to come into direct contact with the plant. This is because a more rigid material, such as horticultural plastic, can damage delicate growth when buffeted by wind. Recycled bubble wrap is also an option (it can be patched together with horticultural tape). The disadvantage of non-permeable material, however, is that a plant can ‘sweat’ beneath the cover and attract fungus in the humid temperatures created on warm days.

Overwintering pest insects can also spring into action in these conditions. If you have no choice but to use plastic, place it over a frame made of waste wood, or construct a teepee-style frame from lengths of bamboo pushed into the ground. Cover these constructions with the plastic so it doesn’t come into direct contact with the plant, and ventilate from below by propping up the material in two or three places with bricks. Leave a small opening at the top. If you’re not a builder, visit your local land transfer recycling
centre, and you’ll be amazed at the variety of frameworks you’ll find there! Clothes pegs and bulldog clips are smart ways to hold plastic closed around a frame.

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