is not all bad news, however. Counterintuitive though this may seem, hilltop sites often enjoy far less cold and fewer frosts than surrounding gardens. The reason is simple: cold air sinks, meaning that wintery air drains freely off gardens on elevated sites and whisks away the chances of frost as it goes. If the garden is in the south of England, or even just faces south, this effect is even greater. Of course, if the hill we are talking about is of Alpine proportions these benefits start to diminish, but for most hills under about 400m above sea level (which is pretty high by UK standards) there is a definite benefit.
Type 3 – Lowland frost pockets
As mentioned above, dense cold air has a habit of running downhill, and if you live at the bottom of a hill, the accumulation of this chilly air can create intensely frosty conditions. This is particularly true in valleys and ditches, where frosts often arrive earlier and end later, making winters not only colder but also in effect making them last longer. This means that many of the more tender plants can find it difficult to survive in these areas. Rest assured that British native species – perfectly adapted to freezing cold winters – will grow away as if nothing ever happened.
Every cloud has a silver lining, however. Lowland frost pockets are often sheltered from the full effects of strong drying winds and are also less likely to suffer in times of drought – water, like cold air, flows downhill. This makes them a great place to grow hardy, moisture-loving species like marshmallow, willow, cranberries, angelica, meadowsweet, watermint and comfrey (great for making organic fertilizer).
Type 4 – Seafront sites
As the palm trees (Phoenix canariensis, Trachycarpus fortunei, Chamaerops humilis) that increasingly line seaside resort promenades attest, coastal gardens enjoy mild, sometimes even frost-free winters. Generally, the closer they are to the sea, the lower the chance of frost. They also have the rather dubious honour of being amongst the wettest places in the United Kingdom (with the exception of coastal Norfolk, Suffolk, Essex and Kent), but from a gardener’s perspective this does mean very little watering is ever necessary. They also tend to be relatively well drained because most coastal sites have a sandy, friable soil, which means this extra rainfall does not result in the waterlogged soil that so many medicinal plants, and particularly herbs, hate.
These wonderfully mild conditions do come at a price, however, in the form of the huge gusts of salt-laden winds that blow in off the sea, especially in the winter months. Such winds can have a particularly damaging effect on plants, particularly soft, leafy species. Despite this, and with a few cleverly planted trees or hedges to act as windbreaks, you can create a space that enjoys the best of both worlds: mild, moist conditions sheltered from the full force of the winds. Abbotsbury Subtropical Gardens on the south coast is a perfect example, where a dense barrier of evergreen trees have created a sheltered microclimate with stunning results.
Soil science
Apart from planting wind breaks or creating heat-retaining walls, there is not an awful lot you can do to significantly change the climate of your site (short of building an enormous Eden Project-style dome over it). You can, however, radically improve your growing conditions – by improving your soil.
Soil quality has a direct impact on the health of your plants. By making small adjustments to this, you can dramatically change not only how well your plants grow but even which species it is possible to grow on your site.
To improve it, you first need to figure out what kind of soil you have, and the good news is you don’t need a ‘CSI’-style lab to analyse it. Just grab a handful of soil on a dry day and give it a good squeeze. Then ask yourself:
A Does the soil break up easily, feel a bit gritty, and filter through your fingers?
B Does the soil clump together, look slightly shiny, and roll easily into a firm sausage shape?
C Does the soil roll into a loose, fragile, sausage shape?
A It’s sandy soil
Many Mediterranean-type herbs and plants (fennel, lavender, lemon verbena, olive, rosemary, scented-leaved pelargoniums, thyme) thrive on this kind of soil because it is as close as possible to that of their native environment, to which they are perfectly adapted. Being wonderfully free-draining, this type of soil does not suffer from waterlogging and is extremely well aerated.
While many plants love this soil, there is a major down side to its open, friable texture: water and nutrients tend to drain straight through it. This means that it can often hold too little of these essential elements to support the healthy growth of many species that aren’t specifically adapted to cope in these harsh conditions.
There is, however, a very simple way to greatly improve the water- and nutrient holding capacity of sandy soil: every year, apply a good layer of organic matter (compost, leaf litter, well-rotted manure or even just leftover vegetable peelings which have been rotted down in a compost bin). This organic matter acts like a sponge to retain water and the nutrients dissolved in it, and make it available to the roots of plants. If you want to, feel free to dig the matter in, but this is not strictly necessary. (If you’re wondering why, see ‘To dig or not to dig’ below for a full explanation.)
B It’s clay soil
When the tiny particles of clay meet water, they stick together, making this soil clumpy and heavy. This makes it far superior to sandy soil in terms of its excellent water- and nutrient-retaining properties, but its dense, pastelike consistency can restrict the flow of air to, and the uptake of nutrients by, the plant’s roots. Many half-hardy plants that do not survive the winter are not necessarily the victims of the cold itself but instead succumb to the stifling effects of waterlogged soil, which cause bacterial or fungal infections that rot the roots. Clay soils also have a tendency to bake rock hard in hot, dry summers, just like pottery in a kiln, leaving your plants struggling to grow in what is almost a natural concrete.
Just like sandy soil, the addition of organic matter every year will greatly improve the condition of heavy clay soil. Here the fibrous texture of organic materials like compost or leaf litter opens up the soil structure and allows air in. Additionally, digging in some grit or horticultural sand will break up the heavy clods to improve drainage. (Whatever you do, though, please don’t use builder’s or beach sand, which contain plant-damaging lime or salt.) You’ll find that the soil becomes freer-flowing and less likely to waterlog, with a texture more like the topping of an apple crumble than dense cookie dough, which gives plants a far better chance.
C It’s loamy soil
Congratulations! You have the soil type that all other gardeners want, the perfect mixture of water- and nutrient-retaining clay and friable, well-drained sand. You get different variations of this (more clay than sand, more sand than clay), but on the whole this soil is ideal for growing the widest range of plants. Having said this, excellence can always be improved upon, and (again) this is achieved by piling on the organic matter every year to keep the nutrient levels high.
To dig or not to dig?
The first point to note is that garden compost, leaf mould, well-rotted manure or other bulky fertilizers are all considered to be organic matter; granules, pellets or liquid feeds aren’t.
Now, adding organic matter to soil aerates and enriches it, but there is a big debate about whether you should dig it in, or just leave it on the surface and let the worms do the work for you. Being a resolutely lazy gardener, I prefer the second option. Shovel on a load of organic matter in autumn, then leave it over the winter. By next spring the worms will, hopefully, have worked their magic, though you can lightly fork it in then if it’s still clumpy. If you opt for the no-dig approach, you have the added bonus of using the compost layer as a mulch before the worms get to work. This will keep weeds down and moisture in – as well