10 tips to protect plants from killer frosts - the pros use them and you should, too

If you're busy wondering how to protect plants from frost, we don't blame you: things are about to get very cold indeed, with widespread overnight frosts and foggy mornings forecast for the end of this week.

Now, we already know that overwintering is crucial for a happy garden over the winter months – and that you should never walk on grass when it’s frosty, too. Still, there is plenty more we could and should be doing to protect our plants from freezing temperatures.

'You can get a ground frost that affects lawns and roots, and an air frost that affects stems, leaves, flowers and fruit,' warns Kate Turner, gardening expert at Miracle-Gro. 'Water in the plant’s cells freeze, expand, then burst, leaving the plant unable to take up water and nutrients.' 

How to protect plants from frost

While frost damage can be a particular problem in a north-facing garden, which will feel colder and get less sun, it can impact any and all outdoor plants if the mercury dips low enough.

To help you keep your garden looking its very best, then, we asked gardening experts for quick and easy tips to protect your plants from frost...

1. Protect delicate plants with plastic bottles

You don't have to spend a fortune to protect plants from frost; you can actually recycle old plastic bottles to keep them safe in the harsh winter weather.

'Recycle your plastic bottles and create a homemade mini cloche, by cutting the top and bottom of the bottle and placing it around the plant, to protect delicate leaves on young plants from chilly temperatures,' says Jack Sutcliffe, founder of Power Sheds.

If you're on an upcycling kick, he adds that you can also 'line the floor and walls of your shed with old rugs or offcuts of carpets to insulate and protect your shed from any potential mould or damp that could build up and damage belongings'. 

2. Wrap plants in fleece to protect from frost

‘Larger, more tender plants may need fleecing to help protect them from the cold and frost, especially if there is a forecast drop in temperature,’ says Andrew Lawson, head gardener at the world-famous Tresco Abbey Garden. 

‘Fleecing is a thin, nonwoven fabric which is used to protect both late and early crops and delicate plants from cold weather and frost. It’s very easy to use: simply wrap your plant with it (make sure it’s not too tight), or put it on top of your patch, whiles making sure it’s nice and secure with pegs or string.’

Andrew Lawson

Andrew Lawson joined Tresco’s world-famous Abbey Garden in 1985 as a Propagator, and was made Head Gardener in 1995. He has vast experience within the horticulture industry, constantly researching and finding new exotic plants from across the globe while also maintaining the gardens for visitors.

There are lots of horticultural fleece brands available, but the SA Products garden fleece at Amazon is highly rated. Alternatively, Jack suggests using old bedsheets.

'Placing a lightweight bed sheet over ground plants helps to prevent any gaps of cold air from seeping into leaves and flowers,' he says.

Whichever you choose, remember to remove the cover during the day so that your plants can gain nutrients from the sun. 

3. Bring pots inside to protect them from cold

Overwintering is one of the best ways to protect plants from frost, but it's also worth remembering that you can move potted plants indoors if a frost warning has been issued, as long as the pots aren’t too heavy to lift. 

‘Potted plants can be moved into a shed or garage overnight to protect them from frost,’ says Nick Hamilton, head gardener at Barnsdale Gardens.

Nick Hamilton

The son of renowned gardener Geoff Hamilton, Nick is a respected horticultural expert in his own right. After Geoff passed away, Nick took over ownership of Barnsdale Gardens, which his father established in 1989. These idea-filled gardens continue to provide inspiration for home gardeners today. 

If you’re fortunate enough to have a greenhouse or similar, then move outdoor pots there until the cold snap has passed.

‘If you have plants in pots outside, now is the time to think of moving them into a well-lit position in a conservatory or cold glasshouse to keep them fairly dry as cold and wet together is usually more damaging,’ adds Andrew.

4. Spray garlic around your plants

You might know how to grow garlic already, but did you also know that this delicious vegetable is a tried-and-tested way to protect plants from frost? Or, rather, from hungry slugs and snails that come out to feast in the winter?

'Winter is the perfect time for pests, such as ants and slugs, to invade garden plants and destroy opportunities for growth when spring comes,' says Jack. 'The pungent smell of garlic will repel any pesky pests without damaging the plants.'

Top tip: blend garlic with a little water to create a spray that will be easy to spread around the garden. 

5. Wind bubble wrap around your pots

When sussing out how best to protect plants from frost, remember that you can take steps to insulate pots, which will protect both the soil and roots of the plants from freezing in frosty weather. 

'Trap warm air around your potted plants by wrapping the pots in bubble wrap,' suggests Jack. 'Cold weather, particularly frost, causes the water in plant cells to freeze, but bubble wrap can help them to survive windy winter weather.'

Wrapping pots will also help to prevent containers from cracking as they freeze and thaw in cold weather, so this is a good tip if your patio ideas feature lots of colourful containers that you don't want to split in the frost.

Kate adds that, for even more protection, you should 'group containers together and near a wall or under trees and shrubs.’ 

Huddling the containers together can help to protect them when there’s a big freeze from sudden frosts.

6. Cover plants in soil or bark

If you're looking for more ways to protect plants from frost, remember that mulching is a brilliant way to offer an extra layer of insulation to plants.

Nick is a fan of this fast fix, temporary solution, insisting it's the best course of action when frost is forecast and there’s no time to buy horticultural fleece before it strikes. 

‘Mound some bark or soil temporarily over the crown of the plant to protect it – if you don't have either, then newspaper would do,’ he says.

This works for more tender perennials that are planted in the ground, so can’t be moved – so be sure to use it for your flowerbeds and garden border ideas. 

7. Pack your trees with straw

Just as you might pop on a puffa jacket to keep you warm on a cold day, the same is true when it comes to finding ways to protect plants from frost. And, if your garden is filled with the best trees for small gardens, it's well worth wrapping them with straw.

‘You can protect your trees and shrubs from frost by packing the branches with straw or bracken, and securing this with fleece and ties,’ says Kate. 

‘At the same time, check your tree ties and stakes and replace, tighten or remove as necessary, ready for any stormy weather.’

Remember, though, that this is not the speediest fix, so you may want to try it when the weather forecast is predicting a prolonged cold snap, or at the start of the winter (think of it as your trees’ winter wardrobe).

8. Mulch garden borders

We know that mulching borders can help to prevent weeds, but it’s also great for protecting plants during a cold snap – essentially, you’re laying a ‘duvet’ of mulch to keep your flowerbeds warm. 

‘To protect soil and plant roots from freezing and help retain moisture, mulch plants in thick borders with Miracle-Gro Fibresmart mulch,’ suggests Kate.

9. Got a greenhouse? Keep it toasty

Monty Don is ditching his heated greenhouse this year, prompting many amateur gardeners to do the same, but that doesn't mean you can't still use yours to protect plants from frost.

'When there is a sudden frost, keep an eye on greenhouse temperatures. A night minimum of 4º or 5ºC is a safe temperature to maintain if you want to be safely buffered against severe snap frosts,' advises Tom Barry, CEO of Hartley Botanic.

You can spread horticultural fleece over vulnerable plants during excessively cold spells, but there's another way to warm the soil and to protect your plants from a sudden frost.

'One of the most economical heating techniques is simply to warm soil, either in a bed or propagation bench. Soil-warming cables provide heat where it is most needed, at the roots, so even if top growth is cold-damaged, the roots will survive,' explains Tom. 

'Cable is safe and easy to install and, with a thermostat, lets you control soil temperature more accurately. It is particularly useful for protecting young plants in cold times of the year. Its performance depends on the cable type, prevailing temperatures and how the system is installed – for example, a 6m cable consumes 75 watts, and correctly installed will sustain temperatures between 15°C and 25°C per square metre of covered bench. Cover plants with fleece or a canopy of translucent sheeting to retain heat.'

10. Water plants before the frost arrives

It may seem counterintuitive – after all, frost is just frozen water, right? – but the experts say to water your plants before any sudden frost.

'This will ensure they have received essential nutrients and are standing strong when the frost arrives,' explains William Mitchell, owner of Sutton Manor Nursery. 

Watering ensures your plants don't get dehydrated as they can't absorb frozen water. 'Also, the moist ground will also stay warmer than it would if the soil was dry,' says William. 'But note that watering plants isn't necessary if it is going to rain before the frost comes, or if temperatures are already freezing.'

FAQs:

Now that you know how to protect plants from frost, it's time to wrap up warm and get outdoors, stat! There's a cold snap on the horizon, and we'd all best get to work quickly if we want our gardens to look their best...