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10 top tips for ensuring your garden is frost-proof this winter

There are many reasons for the surprisingly large variations in temperature that you will get even in a tiny garden - Andrew Crowley
There are many reasons for the surprisingly large variations in temperature that you will get even in a tiny garden - Andrew Crowley

The climate is uppermost in many gardeners’ minds now, with frosts here, and there’s no doubt that the more you know about your own microclimate, and how to adapt and alter it, the more you will be able to get out of your garden spaces and plants.

I was not so obsessed with this before, but having worked with Peter Gibbs (formerly from the Met Office and a BBC weatherman) on Gardeners’ Question Time, my eyes have been opened. This month I have tapped his vast knowledge and hopefully helped to explain why raised beds are often warmer, why climbers can be so slow to get growing, and how to enjoy north-facing spaces. I am tempted to emulate him and invest in my own mini weather station!

The first frost of the year

Getting to know your garden’s microclimate is fascinating as it allows you to exploit the temperature, rain and wind variations to the full. Walled gardens with their protected microclimate were vital for food production for centuries. I was mighty surprised on drawing the curtains recently to see a ground frost on the north side of the house on October 9 – exceptionally early. I had to touch the grass to convince myself it was not a heavy dew.

Later that day I was working in Ely (30 miles south east) and several people said all their dahlias had been frost-blackened. Mine, luckily, are still voluptuous and colourful as they are in the south-facing, sheltered courtyard garden which is frequently 10C or so warmer than the frost-hit north-facing garden that overlooks our old meadow.

When I checked my French beans, courgettes and outdoor tomatoes (in raised beds) which are also grown on the colder, north side of the house, they were all unscathed. This is because raised beds and containers above ground level enjoy warmer temperatures than the colder temperatures at ground level. It is all down to microclimate.

Temperature variations in a garden

I worked with Peter Gibbs recently, formerly of the Met Office and a BBC weather forecaster (and, of course, co-chairman of Radio 4’s Gardeners’ Question Time). He highlighted the many reasons for the surprisingly large variations that you will get even in a tiny garden. In his garden, which is around 10m by 30m, he has seen temperature differences of 8C, and it is not unusual to see this difference over a mere 10 metres.

Getting to know your garden’s microclimate is fascinating as it allows you to exploit the temperature, rain and wind variations to the full - Andrew Crowley
Getting to know your garden’s microclimate is fascinating as it allows you to exploit the temperature, rain and wind variations to the full - Andrew Crowley

“The difference will be greatest on a windless day with strong sunshine as a breeze will stir things up and even it out a bit. That is, of course, true air temperature, without the sun shining directly on the thermometer,” he points out.

It is fascinating to check out the temperature differences. A quick and fairly accurate way to do it is to put similar-sized small pieces of wood, about one-inch cubes, in various places around the garden (out of direct sun) and measure them when you have allowed time for them to get to the surrounding temperature, with an infra-red temperature gun with a red spot to focus.

Digital maximum and minimum thermometers are indispensable in the greenhouse, especially after last summer’s highs of 40C, as well as for extreme cold.

Colder temperatures at ground level

So why exactly did my vegetables on the north side escape the frost? What most people do not realise is that meteorologists read air temperatures at a height of between 1.25m and 2m, usually in a Stevenson screen, so the thermometer bulb is out of direct sun. But the temperature on the ground is pretty much always lower than the temperature at around eye level.

The temperature on the ground is pretty much always lower than the temperature at around eye level - Andrew Crowley
The temperature on the ground is pretty much always lower than the temperature at around eye level - Andrew Crowley

It may even be up to 6-7C lower, with free draining sandy soils showing greater extremes than wet clay soils. This is because the ground surface loses heat to space, with the coldness starting at the ground and working its way up. Wet, clay soils will emit more heat than dry, sandy ones.

Frosts and rain prediction using weather apps

Frosts are the bane of gardeners, affecting flowers, fruit and vegetables. In my early years of gardening I would look up at the sky on clear, sunny spring days and hastily throw fleece over crops susceptible to frost. Now there are great weather apps available and I rely heavily on these. Peter Gibbs points out that the most accurate forecast models for the UK are the Met Office and the ECMWF (European Centre for Medium-Range Weather Forecasts) so the two apps that Peter rates are the Met Office app which uses its own data and the BBC app which is a blend of the forecast models.

But, if you are experiencing showery weather and it’s crucial to know an accurate rain forecast, he recommends you use a weather radar app such as Rain Alarm. This should tell you that rain is coming within 15-20 minutes. Peter has a Bresser weather centre in his garden (bresser.de) – these cost from £130.

Different types of frosts

There are several types of frosts: ground frost, air frost, hoar frost and rime. The ground frost is when the frost is, as it says, on the ground, with the air frost occurring when it is freezing or below around 1.5m above the ground (ie far colder than just a ground frost). Hoar frosts are visible manifestations of humid air crystallising out on plants and objects, while rime builds up as beautiful feathery layers on trees and shrubs as supercooled water droplets freeze on contact, often seen after a foggy night in winter.

The advantages of frost

Although freezing temperatures and frosts and can adversely affect plants, they have their upsides, too. They can kill off build-ups of pests and disease in plants and soils. They also help break down compacted soils, producing a beautiful crumb structure. I love working in the garden on cold, frosty days, doing warming work such as spreading mulch, axing logs and turning compost. I have to admit I can be slow to start but once stuck in I am invariably reluctant to go back indoors.

Rain shadow effect

Many gardeners complain of climbers on walls and fences taking ages to get going, and I think this is nearly always down to their lack of awareness of the all-important rain-shadow effect. Most of our moisture-bearing winds come from the south west, and close-board fences, hedges and walls that interrupt the moisture-laden winds will have far larger deposits of moisture on the south-westerly side and next to nothing on the leeward side.

Most of our moisture-bearing winds come from the south west, which can impact how long it takes some plants to get going - Andrew Crowley
Most of our moisture-bearing winds come from the south west, which can impact how long it takes some plants to get going - Andrew Crowley

The difference in rainfall can extend a fair few metres beyond the fence line. Also, when you are planting borders adjacent to the building, the same effect happens, but the walls can actually draw moisture up from the ground and you may well have some roof overhang too, both of which increase the dry effect.

So when you are establishing new plants in rain-shadow situations you do need to compensate. On planting, soak the plants before they go in, soak the hole before they go in and soak again after planting. Watch new plantings like a hawk and as soon as you see the slightest flicker of stress, give a really good soak. With any new planting I tend to soak weekly in the growing seasons but with good volumes of water, around two gallons per three-litre plant, as a very rough guide. That way the roots chase the water down and so they will develop a good deep root system. Frequent, shallow watering encourages surface rooting, which is detrimental.

Garden orientation

North-facing gardens do get bad press, but our main sitting area is on the north side, and it does get quite enough sun at the times of the year we use it. I have tall, highly productive espalier pears against an 8m-high barn and my silver-leafed, Verbascum bombyciferuim ‘Polarsommer’, which loves sun, self-seeds and flowers all along the bottom of the wall. In north-facing borders the soft, clear light means that blues and whites are especially effective and strong colours don’t get burnt out in harsh sunlight. I love watching the early morning sun spill across our north-facing garden in the morning before it tracks back in the opposite direction in the evening.

Many roses perform well on north-facing walls apart from the beautiful but usual suspects, repeat flowering Rosa ‘Mme Alfred Carriere’ and R. ‘Phyllis Bide’. Most of David Austin’s English roses perform well too. What many roses struggle with is dry shade under trees.

I love watching the early morning sun spill across our north-facing garden in the morning - Andrew Crowley
I love watching the early morning sun spill across our north-facing garden in the morning - Andrew Crowley

My cousin has a fabulous garden, but he says if he could improve it he would reorientate it so it faces west. Then he could enjoy the evening light in the garden when he gets back from the office. South-facing gardens are always thought to be the best, but I think with climate change maybe they are losing their edge as we put up pergolas, parasols and loggias to escape from the heat. Who would have thought we would have had temperatures of 40C in the UK and no doubt that will be topped pretty soon.

Climate change

Few gardeners can be unaware of the effects of climate change. It seems that our job is really about giving plants the best chance to get through the greater extremes we are experiencing. Often milder, wetter winters are followed by extremely dry summers. Making sure the soil drains but also holds moisture is key. To that end, piling on organic matter (free sources of ramial and compost in my case) can only be a good thing. Of course we should not get lulled into believing that we will not have sharp, cold snaps with plummeting temperatures and must be on our mettle with fleece and covers waiting in the wings.

Using protective covers

But back to freaky frosts. When one is forecast you can use fleeces, which are brilliant for keeping off a few degrees of frost. Agralan (agralan.co.uk) sells a 17g/sq m fleece that protects plants from around 2-3 degrees of frost (left) and a thicker 30g/sq m, which provides 6Cof protection.

When we get extreme cold, I bring my precious tender plants (such as my curry plant, Murraya koenigii) under a lean-to and fling old quilted coats over them, supported on canes – very makeshift, but it works. In the greenhouse you can make a box of polystyrene, to insulate your treasures. It always amazes me to think that a thick 24in stone wall has the same insulation value as a 9in brick wall or a ¾in polystyrene sheet, so it makes sense to save this valuable packing material.


What do you do to ensure that your garden is frost-proof as winter approaches? Share your tips in the comments section below