Most gardeners are unaware that the natural flora of mediterranean-climate regions is a lot richer than that of temperate regions.

The flora of the Mediterranean basin is one of the richest in the world: 25,000 plant species grow here, which amounts to 10% of the world's flora.

A good indication of this diversity is the fact that it is often in dry regions that we find the greatest number of endemic species. The Cape Province of South Africa, for example, which enjoys a mediterranean type climate, has an amazing 5,800 endemic plant species - compare this to Great Britain where, in an area three times larger and with a damp climate, there are only 24 endemic species.

Do you know how many species you need to create a garden? The answer is somewhere between 100 and 200, perhaps slightly more if you have a large garden or if you are a passionate plantsman.

The soil is generally acid and shrubs such as Fabiana imbricata, Escallonia rubra and Buddleja globosa can be found, while in the foothills of the Andes remnants of the ancient Araucaria forests survive.

In spite of the intense drought and heat, Atriplex canescens thrives in the dunes of Death Valley. It is a shrub that is easy to grow in the garden since it withstands cold well and tolerates a variety of soil conditions. With its fine foliage and gracefully arched inflorescences, it is without doubt the most ornamental of all Atriplex species.

It is the plants mechanisms of adaptation to drought that give the Mediterranean garden its charm, its profound identity and unique character, for it is only in an unwatered garden that the beauty of dry-climate plants can truly be seen. If we use plants that are adapted to dry conditions, then the drier the garden, the more beautiful it becomes.

Survival strategies:
Dying in summer: annual plants
When the heat of the summer arrives, annuals are not in the least bit bothered because they are already dead. However, they have already dispersed their plentiful seeds, thus ensuring the survival of the species and the cycle is ready to begin all over again.

Nature is generous with annual plants, endowing them with attractive and brightly coloured flowers, for the plant can't afford to waste time: it needs to attract pollinators as fast as possible before the summer heat sets in and death approaches.

Hiding below ground: geophytes
Geophytes are what we generally call bulbous plants. Specialists make a distinction between true bulbs, resembling an onion (tulips, narcissi), corms, which are a swollen basal stem (Crocus, Sternergia), tuberous rhizomes, which are fleshy horizontal stems (asphodels, many irises), and tubers, which are shorter and thicker than rhizomes (Jerusalem artichokes).

A double root system
Many dry-climate trees and shrubs develop a double root system in order to cope better with a shortage of water.

Imagine a Cistus seed germinating in the garrigue in autumn...Over winter the seedling doesn't see to grow more than a few centimetres - but in fact its most important growth isn't visible since it's taking place out of sight below ground. The Cistus is rapidly sending out a long taproot deep into the soil, forcing its way down between the stones. If the plant manages to survive its first summer, in addition to its deep root system the Cistus will then also develop a branched network of surface roots.

A number of Mediterranean plants adapted to degraded and often very poor soil have developed a symbiotic relationship between their surface roots and mycorrhizal fungi which help the plant exploit the small amount of decomposing organic matter on the surface of the soil.

Reducing transpiration: Sclerophyllous plants
In order to limit transpiration, sclerophyllous plants have developed thick, leathery, evergreen leaves with an upper surface covered with a glossy and impermeable cuticle. All the stomata are on the underside of the leaves, the side most protected from the sun.

The garrigue and maquis around the Mediterranean contain many sclerophyllous plants: holm oak, arbutus, phillyrea, bupleureum, buckthorn, lentisk, myrtle.

Thanks to their evergreen foliage sclerophyllous plants grow in autumn, winter and spring and then become dormant in summer, the 'off-season' for Mediterranean plants.

Summer dormancy: plants that lose their leaves in summer
While sclerophyllous plants opt for a period of summer dormancy, some dry-climate plants have taken this strategy to extremes: they lose their leaves entirely during the dry season.

Reducing exposed surfaces
The term evapotranspiration is used to cover the combined water losses from a plant's leaves.

The rosemary maintains a large leaf surface area to carry out photosynthesis, but folds the leaf edges over in order to reduce the surface directly exposed to the sun, and hence minimise water loss through evaporation.

Many dry-climate plants seem to be vying with each other to see which can achieve the smallest leaf: there are linear leaves (Dianthus pyrenaeus), needle-like leaves (Genista hispanica), minute leaves (Teucrium subspinosum) and leaves reduced to simple overlapping scales (Juniperus phoenicia).

Obviously, reducing the surfaces able to capture the energy of the sunlight also means a decrease in photosynthesis; this explains the slow growth rate of many plant species with very small leaves [Cacti!].

Sheltering from the heat: hairy plants and grey foliage
Plants with grey foliage have developed a simple and effective way of 'getting into the shade': they are covered with white hairs that reflect the sunlight. Beneath these hairs the leaves are green, because photosynthesis can only take place through the action of sunlight on the green pigment in leaves.

On the one hand the dense web of hairs reflects the sunlight and reduces the heat on the leaf surface, thus directly reducing evaporation. On the other, the hairs serve as a 'windbreak', creating a microclimate over the ostioles of the stomata and conserving some of the water vapour produced during the gaseous exchange of photosynthesis.

Capturing moisture from the air
The amount of droplets trapped by the hairs on grey-leaved plants is significantly greater than that simply deposited on ordinary leaves.

In arid climates with almost no rain, some plants even manage to survive by absorbing through their stomata the small amount of water from nocturnal humidity that is trapped by the hairs on their leaves.

In a bubble of scent
The primary role of essential oils is to protect the plant against predators, either herbivores or insects. A second, more complex role is to combat competition from other species: the litter of decomposing leaves formed beneath Cistus or thyme plants, for instance, releases substances that inhibit the germination of competing plants.

Conserving water: succulent plants
The tissues of succulent plants have particularly large cells, creating a sponge-like structure which can act as a water reservoir, enabling the plant to get through long periods of drought.

The stems of the succulent euphorbias have large vertical ribs, giving them their characteristic canalised cross-section. The shade projected by these vertical ribs means that a significant area of the stem can benefit from relative coolness during part of the day.

However, the most remarkable adaptation in succulent plants has to do with a modification of the photosynthesis cycle...Carbon dioxide is absorbed through the stomata during the night and fixed by means of a special chemical reaction, then used during the day to permit photosynthesis to take place without opening the stomata - in other words, without water loss through transpiration.

Salt, wind, cold and drought: balls and cushions
Salt acts on leaves like a regular and intense drought. Because of the difference in osmotic pressure, salt literally draws water out of the plant's tissues.

The most effective way for the plant to withstand wind is to grow in a dense ball shape.

A scale of drought resistance
Although there are a number of secondary factors that comes into play, what principally defines hydric deficit is the relation between temperature and precipitation: an increase in temperature causes greater evapotranspiration, while a decrease in precipitation makes water less available to the roots.

...a month is considered dry if its average temperature (in degrees Celsius) is greater than half its precipitation (in millimetres).

Alkaline soils
If your soil is alkaline, as most soils around the Mediterranean are, it's not worth trying to grow calcifuges.

You can grow many species of lavender in alkaline soil, such as Lavandula angustifolia, Lavandula latifolia, Lavandula lanata and a host of others.

Most wild Mediterranean-climate plants can in fact adapt without problem to acid soil, even when their natural habitat is limestone rocks.

Chlorosis is a complex matter, since it depends on the pH value, the level of active alkalinity, plus the type of soil - either more or less 'asphyxiating'. Drainage thus plays an important role: plants become chlorotic much more quickly in compact clay soils that remain saturated with water in winter.

With its tufts of decorative bracts, Lavandula stoechas is particularly attractive. But it only grows in acid soils.

Cold
The duration of frost is at least as important as degree. A drop in temperature to -10C for a few hours just before dawn is not at all the same thing as when the thermometer remains at -10C for several weeks at a time.

Depending on the suddenness of the frost, the degree to which plants have been grown hard also influences their sensitivity.

Many Mediterranean plants can tolerate dry cold, but will die under the combined effects of cold and damp.

The age of a plant also affects its resistance to cold. A well-established plant can put out fresh growth from the rootstock after a harsh winter, while a young plant, still weakly rooted in the soil, won't have the strength to send out new shoots in the spring.

Finally, we should note that an individual species may have different 'ecotypes': during the course of its evolution, the species gradually adapts to particular conditions, such as cold, in a given site.

Small and tough: a new criterion of quality
The harsher the climate conditions, the more we need to plant small plants which have been grown hard.

When you choose your plant, the key word is balance. The volume of foliage above ground must be balanced to the volume of the root system.

Root quality
Root quality is a taboo subject in the horticultural world. Everyone knows there is a problem, but no one wants to discuss it.

The more the plant grows, the more the roots twist: if the plant remains too long in the pot, the roots go on twisting until they have formed a tight knot. This is sometimes known as 'root girdling' or 'root circling'

In the case of woody plants - trees, shrubs or sub-shrubs - there is an even more serious consequence: if the plants finally does manage to become established, the base of the trunk will slowly grow wider until one day, after five or ten years depending on the species, the collar of the plant will be strangled by the circular knot of roots formed in the pot. This is one of the main causes of premature death - often wrongly attributed - of woody plants in the garden.

The problem of the root knot is less serious for herbaceous perennials since they regenerate by suckers, layering or rhizomes.

Soil preparation
In the course of their evolution, dry-climate plants have adapted to soil conditions which may seem harsh, but which suit them perfectly: not good, deep, moist soil, but rather a soil that is stony, poor and well-drained.

Above all, dry-climate plants need good drainage. Drought doesn't scare them, it's what they're designed for.

The simplest way to drain your soil is to raise your beds.

If the soil is really clayey, it is best to mix it with river, or sharp sand at a ratio of up to 30-50% sand...But take care that you have the right kind of sand: sharp or river sand has grains that are rounded, and improve drainage, while quarry sand, produced when rock is crushed, has pointed grains that make clay set as hard as concrete.

When to plant
Drought adapted plants have a growth cycle which is the opposite of that of temperate climate plants: they grow in the autumn, winter and spring, followed by a marked dormant period in summer when the heat sets in.

Rapid growth is not what is wanted during the plant's first year. No potting compost or fertiliser should be added.

It is only during the second year that the plant will increase visibly in size, often in a spectacular manner, as if to make up for lost time.

In the dry garden plants grow a lot faster than might be imagined, provided of course that the initial rules have been respected: choosing drought-adapted species, preparation of the soil and autumn planting.

The planting hole and watering basin
A young shrub grown in a 1 or 2 litre pot requires a hole at least 30 cm wide and 40cm deep, which is equivalent to the average volume of roots after the first year.

Don't add peat, don't add compost, don't add manure!

If at all possible avoid plants raised in a medium that is too rich in peat: as soon as the rootball dries it will shrink like an old sponge, so that instead of remaining in contact with the soil in the planting hole the roots will suddenly find themselves in an air bubble.

Now for the watering basin - perhaps the most important thing of all. Novice gardeners always tend to make the watering basin too small, which is more or less useless.

The size of the basin depends on the nature of the ground - how permeable it is - but in general a good basin should be at least 60cm in diameter and 20cm deep, in order to hold 20-30 litres of water at a time.

When and how to water
The best way to get a young plant accustomed to drought is to water as infrequently as possible, but copiously each time - the water must form a patch of moisture deep in the ground, well below the level of the rootball, in order to 'draw' the roots downward.

Repeated superficial watering makes the plant produce a thin carpet of roots just below the surface, exactly where evaporation is greatest.

Sprinkler irrigation favours the development of surface roots to the detriment of deep ones. It also encourages the germination of countless weeds and favours the appearance of many diseases such as rust, Oidium, Aescochyta and Phytopthora.

In rocky soils, wonderful damp pockets remain even longer beneath large stones - a real delight for roots.

Hoeing the surface of the watering basin a few days after watering limits water loss through evaporation.

If you use drip irrigation, you should programme it to provide a deep watering at widely spaced intervals, as in watering basins.

For those who insist, a question of zones
If you are going to water some of the plants in your garden there is one error you should avoid: mixing species without taking into account their water requirements, then irrigating them all in the same way.

Your garden can thus be visualised as a series of concentric circles spreading outwards from the house. The further from the house you get, the drier the garden, while close to the house, in a zone that is easily accessible for watering, you can group the plants which have higher water requirements.

To replace smaller areas of lawn you could, however, choose from a range of ground cover plants adapted to the Mediterranean climate which will tolerate a moderate amount of being walked on, equivalent to normal family demands. Some of these plants withstand drought relatively well (Phyla nodiflora, Achillea crithmifolia, Cynodon 'Santa Ana'), while others will need a weekly watering in the summer (Zoysia tenuifolia, Frankenia leaves, Thymus ciliatus).

From weeding to mulching
It's a good idea to be sensible at the planning stage of creating your garden: rather than planting the entire garden in a single season, it's worth doing it bit by bit in successive years, so that the maintenance of your new plantings during their first year is easier.

It is better to leave the watering basin fully exposed during the first year, both so that the amount of water given to the plant each time can be controlled, and so that the surface of the basin can be hosed when necessary. Moreover, a thick mulch piled closely around young plants can actually retain too much moisture round the base of the plant and lead to the appearance of fungal diseases.

We use two types of mulch. Between large-growing plants we spread a thick layer of organic mulch...Between smaller plants we prefer to use a mineral mulch.

The numerous different colours and grain sizes of gravel available make it possible to set off foliage to its best advantage. In our garden we mainly use calcareous gravel, with a grain size of 10-30mm: the absence of fine particles makes it harder for weeds to germinate.

Pruning
Many Mediterranean plants actually like being pruned each year. Lavenders, Santolinas, Rosemaries and Cistuses [and Teucrium] can all be lightly sheared in autumn in order to maintain their compact shape.

If constricted rootballs are the most common cause of premature plant deaths, the second most frequent cause is certainly the fact that conditions in the garden are in fact too favourable for a great many native Mediterranean species.

Pests and diseases
To avoid diseases in an ornamental garden, I recommend two simple principles, which we apply in our own garden: first, increase biodiversity and secondly use as few chemicals as possible.

Avoid monoculture in hedges, perennial and shrub borders, and groundcover. The more plant diversity you have, the less risk of disease there is.a paragraph. Click here to add your own text and edit me. It's easy.