When fall weather remains warm, it's easy to be lulled into a false sense of security, especially where certain garden plants are concerned. Yet, with the sun much lower and the days much shorter, the nights can be surprisingly chilly.

Waking up to an unexpected early frost can take many gardeners by surprise. It can also take out a number of vulnerable plants before their time, if we're not properly prepared.

Knowing how to protect plants from frost and which ones to prioritise can extend the life of ornamentals and edibles that may still be growing when temperatures suddenly drop. Find out which of your prized plants to keep an eye on and what to do to save them from a cold snap according to experts. This decorative thermometer from Lowe's also makes monitoring outdoor temperatures easy.

Recognizing a Frost Risk

There are certain signs we can look out for that hint that an "unexpected" frost may be on its way.

'I start paying attention when overnight temperatures are forecast to fall into the mid-30s, since frost can form on plant surfaces even when the official air temperature is a few degrees above freezing,' says landscape designer, Kat Aul Cervoni, founder, Staghorn Living. 'After a frost, the most obvious signs of damage are darkened, water-soaked, limp, or translucent foliage which then often turns brown or black.'

'A frost cloth, sheet, or cold frame is usually able to protect plants when the air temperature is above 30°F,' says Kate Copsey, author, New York & New Jersey Gardening. 'Between 30 and 32°F, frost is less severe and frequently spotty.

'Cold air is dense and rolls downhill, so the coldest air settles in valleys or at the bottom of a slope. Garden plants at the lower end of a slope can be killed while plants higher up are fine. The areas directly around walls benefit from a few extra degrees of heat which keeps them warmer a few days longer.

'These very site-specific areas of warmer/cooler air are called “microclimates.” Winds that move the air around help keep frost from settling, and cloud cover keeps some of the warm fall heat from escaping.'

1. Tender Annuals

Most gardeners are philosophical about tender annuals. Realising they have a limited life expectancy, many people are content to let them go when the time comes. However, that doesn't mean we have to give up on them earlier than necessary. With a little effort, it is possible to extend their life a little longer.

In New York, some of the first plants landscape designer, Kat Aul Cervoni pays attention to when an early frost looms, are coleus, impatiens, begonias, zinnias, and basil.

'Many of these can get zapped with even a light frost, and some plants, particularly basil and coleus, can show chilling injury before temperatures actually reach freezing,' says Kat.

'Lightweight frost cloth or horticultural fleece is ideal, but an old bedsheet works perfectly well in a pinch. The key is to drape the material all the way to the ground and secure the edges. You're trying to trap some of the warmth radiating from the soil overnight, not just wrap the foliage.

'I would avoid placing plastic sheeting directly against foliage since it can transfer cold to the leaves where it touches them, plus it's easy for plants to overheat beneath it once the sun comes out.'

This burlap frost blanket from Lowe's is breathable, durable and can be cut to the size you require.

2. Late-Season Flowers

Many late-season flowers, such as New England Asters, Golden Rods and Sedum can survive an early fall frost. However, dahlias don't usually fair so well. These beautiful blooms can benefit from frost protection.

'Dahlias are a big one for me,' says Kat. 'Mine are often still blooming beautifully in October, and a single frost can blacken the foliage and bring the show to an abrupt end.

'For delicate plants like dahlias, I prefer using stakes or hoops to support the fabric so it doesn't crush the flowers or stems; keep this in mind if you're considering things like towels, which may be too heavy for plants.

'Put covers on before temperatures drop in the evening and remove them the following morning once temperatures have risen above freezing - the least amount of time covered is ideal.

'Soil that is moderately moist retains heat better than very dry soil, so watering dry beds earlier in the day before an expected frost can help too.'

At H36" tall, this green metal stake from Lowe's can provide a frame to drape a frost cloth over smaller plants, as well as support growth.

3. Warm-Season Vegetables

Where gardeners and growers are less philosophical about losing plants to an early frost is with edimentals and edibles. Most warm-season crops that are still managing to hang on in balmy fall weather will require over night protection. Cold frames are useful here. However, a frost cloth or fleece can be protective too.

'Tomatoes, peppers, eggplants, cucumbers, squash, and beans are particularly susceptible to early frost,' says Kat. 'These are warm-season crops that generally won't tolerate freezing temperatures so will definitely need protecting if you want to keep them going longer.

'On the other hand, crops like kale, spinach, and many brassicas can handle light frosts quite well which makes them excellent choices for a fall veggie garden.'

'Cool-weather crops such as kale and chard can tolerate frost very well,' says Kate. 'Salad crops and cabbages don’t do so well, so cover these when a light frost is forecast.

'If they’re in a cold frame, keep the lid down on frosty nights but lift it again in the morning, as even in October the sun can burn crops if they’re enclosed in a cold frame.'

This premium cold frame from Burpee enables you to extend the growing season for salad leaves and many other edibles.

4. Container Plants

The container plants most at risk of damage by an early frost will not only depend on the type of plant and the region its growing in, but the location of the container within your yard. Some gardens have microclimates, with cold and warm pockets in different areas, putting some pots more at risk than others.

'Cold air settles in low spots, so the lower parts of your garden might experience frost while another escapes entirely,' says Kat. 'Pots deserve special attention because their roots are more exposed and don’t benefit from the same insulation as in-ground plants.

'Tropical plants, tender herbs, and summer annuals in containers are especially vulnerable – for me, my porch ferns are the main ones I have to mind. I generally move anything particularly valuable or frost-sensitive into my garage overnight, but an enclosed porch, or another sheltered location works too.'

A south or west-facing wall can offer protection too, as heat will be absorbed during the day and released at night.

'If you can move containers, that's almost always my first choice,' says Kat. 'If they're too large to move, group them together in a sheltered location, ideally close to the house and away from wind.

'Cover the foliage with frost cloth and, if a more significant freeze is expected, insulate the containers as well. However, protecting a container from a single frosty night is different from overwintering it outdoors. A plant that's hardy in the ground may not be reliably hardy in a pot through an entire winter.'

This 12"x12" timber plant trolley from Lowe's makes transporting containers from one place another much easier. if you're unable to move your containers, this burlap frost blanket from Lowe's makes a versatile protective cover.

5. Young Plants

Fall is a good time to plant many cold-tolerant species, such as pansies and violas. Cold-hardy young plants can be protected from an early frost, by planting them in sheltered positions, such as in front of a south or west-facing wall, watering them in the morning and applying a layer of mulch to the soil.

'Newly planted tender or marginally hardy plants may need extra attention because they haven't had as much time to establish,' says Kat. 'That said, a newly planted hardy perennial isn't necessarily at risk from a light frost simply because it's young - so no need to take real action there.

'It's not necessary to cover the entire garden. Focus on tender plants that are still actively growing, flowering, or producing food that you want to keep going. It’s also ok to let go.'

The best way to protect plants from an early frost is to pay attention to the weather forecast and prioritize the plants you most want to save by planning ahead. That can be as simple as moving containers out of known frost pockets, covering crops with a cold frame or protecting favorite flowers with fleece.

'We also have to know when to call it,' says Kat. 'Frost cloth can help get plants through a light frost, but it isn't going to save a tropical annual through a prolonged hard freeze. Sometimes the better option is to harvest the remaining vegetables, cut your dahlias for a final bouquet, and let go.'