Bond, English

This is one of the commonest method of constructing a brick wall which is more than ½ a brick thick and consists of alternating courses of heads and stretchers.

English bond brickwork
English bond brickwork

The minor wall building materials

Metal

Though important in building is garden use is rather limited but can if used carefully can be very effective. The term metal encompasses a vast range of material, many used since ancient times, and the suitability of a particular one will depend on the individual use planned.

Reinforced concrete

This material combines concrete and steel to create a material with excellent compressive and tensile strength. This provides the potential to provide some very graceful and elegant structures but the complex nature of the material means is design and specification requires specialist expert knowledge.

Concrete reinforcing should not be confused with crack control in concrete, by weldmesh or polypropylene fibres, which serves a very different purpose.

Plastic

Traditional plastic has not been used a great deal in garden construction but the vast range of different forms of plastics means it has great potential. It has the advantage that it is very rot resistant, can be moulded (and some can be machined), pre-coloured and even some is made from recycled materials means it is beginning to be used for more than pond liners and roofing sheets.

Glass

Used for hundreds of years, recent developments in glass technology means this is a material with great future potential.

Peat blocks

Traditionally these have been used to make raised peat beds, but have they have fallen out of favour in recent years as a result of the environmental concerns around peat harvesting and use.

Peat block wall
Peat block wall

Taxonomic rank

This relates to the level within the hierarchy of plant names. The series of taxa for botany are set out in the International Code of Nomenclature for algae, fungi, and plants. Not all plants have an entry for every taxa and above the level of genus there is often a great degree of disagreement as to what belongs where. The important thing is that any plant can be identified by its genus and below.

 

Taxonomic rank

Kingdom

Subkingdom

Division

Subdivision

Class

Subclass

Superorder

Order

Suborder

Family

Subfamily

Tribe

Subtribe

Genus

Subgenus

Section

Subsection

Series

Subseries

Species

Subspecies

Variety

Subvariety

Form

Subform

(The principal taxa or in bold)

The main wall building materials

Brick

Reclaimed brick walling
Reclaimed brick walling

One of the oldest and most durable building materials; its variability, flexibility, durability and strength has made a ubiquitous walling material. Traditionally made from dried earth the centuries of use and development has lead to a very sophisticated produce now mass produced in millions each year in the UK alone.

The earliest bricks were probably made of mud and date back at least 5000 years, and probably considerably more. Modern bricks are still normally made from fired clay (a natural extension of sun-baked mud) but they now come in a vast range of colours and surface finishes. It must be remembered that most facing bricks, while very strong are damaged by frost if their exposed surfaces are saturated with water. The only real exception to this is engineering bricks which are not as absorbent as facing bricks, but are only available in plain red or blue.

 Concrete

The use of concrete dates back at least 2000 years; it was used extensively by the Romans and there are Roman writings on its mixing, placing and use. Though its use has waxed and waned with changing fashions is seems every new generation re-discovers it, finding original uses for it.

Years of use and study have meant that what may appear to be a very simple basic material has become a very complex subject. What is frequently not appreciated is concrete, while having excellent compressive strength1, has so little tensile strength2 that is it regarded by engineers as having none.

Stone

The stone mason is one of the oldest trades and stone walls have been found wherever stones can be sourced. The earliest were probably dry stone walls built from stones found laid on or near the surface of the soil.  The durability and effective ness of these can be seen from the miles of dry stone wall which snake over the North Yorkshire Dales, where the shallow topsoil means the stones could be sourced by gradually picking up stones laid about the fields. Once metal tools had been invented stone could be cut, worked and polished allowing the creation of the pyramids and temples of the ancient world.

Wall detail at Dornoch Cathedral
Wall detail at Dornoch Cathedral

Stone comes in a vast range of forms and this determines it suitability for building and what results can be achieved. As one of the main costs of stone is haulage, traditionally it was sourced close to where it was to be used so lending distinctive local styles to walls.

 

Timber

Though not as durable as stone or brick, its easy of working and availability has meant it has long been used as a building material. It has also has other advantages over brick and stone work: it is a lot lighter, possesses tensile strength2, can be readily coloured with stains and paints, and although it does weather it is unaffected by frost.

Timber pole walling
Timber pole walling

Wood is though a very variable materials depending mainly on the tree species it comes from, but also the environment the tree grew in and the part of the tree it is harvested from. When used in construction this can lead to concerns about its structural strength and for this purpose it is “stress graded” but in a garden context the size of the timbers chosen for aesthetic considerations means this is unlikely to be important.

Notes:

1)      Compressive strength is simply the ability of a material to resist being crushed.

2)      Tensile strength is simply the ability of a material to resist being pulled apart, something that brick, concrete and stone walls actually lack. Hence the need for arches or solid lintels over openings in walls.

Parts of a Wall

Garden walls are constructed from 5 distinct elements:

Parts of a wall
Parts of a wall

Subgrade

Foundation

Walling materials

Mortar

Coping

 

The first, the subgrade, is the ground the entire structure stands upon and so its stability and load bearing ability determines on whether the wall is going to remain standing. For these reasons the wall foundation should be onto undisturbed ground that has not been built up from material such as old construction rubble or compacted hard core. For the same reason sufficiently deep so that there is no risk of frost and therefore frost heave.

The foundation of the wall is normally concrete and acts to spread the weight of the wall. Historically wall foundations could vary from nothing at one extreme to quiet complex structures and this depends more on the ground conditions and the builder/architect than the date they were built. A roman building could have a concrete foundation not unlike a modern while a country cottage built in the last few hundred years may be built straight onto the topsoil.

The walling material is the bricks, stones, etc. which forms the walls.

The mortar is the sand based material generally used between the pieces of the walling material and it serves the function of keeping the pieces of walling apart. It does not hold the pieces together, so walls have no tensile strength, but instead keeps them apart; so stopping them wobbling and stabilising the structure. The sand itself is held together by incorporating lime or more normally now cement to prevent it being washed out of the joints.

The coping tops the wall and protects it from becoming saturated with rainwater.

Clematis tangutica

Clematis tangutica flowers.
Clematis tangutica flowers.

This charming clematis spices is quite different from the large flowered cultivars usually grown in gardens. The small pixie hat flowers make up for their small size by their numbers which appear from June through into autumn when they can be seen with typical feathery clematis seed heads.  While not as showy as the large flowered cultivars Clematis tangutica (Maxim.)Korch. is a lot less demanding than these tend to be. Like all clematis any reasonable garden soil and aspect is suitable and the small flowers and dense foliage make it more successful in exposed locations where the large flowered cultivars would be pull apart by the wind.

Clematis tangutica
Clematis tangutica

Its vigorous, dense foliage makes it an excellent choice of covering walls and fences. It will reach 4.5 m to 5 m but is not as vigorous as Clematis Montana which tends to rapidly smooth whatever it is intended to grow over. Left to their own devices it will grow quiet happily un-pruned but it can appear untidy. Alternatively they can be cut back as hard as needed in winter though this will delay the start of flowering the following year.

The inside of a Clematis tangutica flower.
The inside of a Clematis tangutica flower.

C. tangutica is very similar to C. orientalis L., the clematis grower Christopher Lloyd admitted he at times struggled to tell the two apart. The main distinguishing feature is that C. orientais has narrower leaves. Originally C.tangutica was classified in 1889 as a variety of C. orientais  by Carl Maximowicz a Russian botanist who travelled widely in the orient. Subsequently Sergei Korshinsky another Russian botanist placed it in a species of its own in 1898. It first reached the UK from St. Petersburg in 1898, but has since been reintroduced from its native habitat in Mongolia and North West China.

Reference:

Species Plantarum by Carl Linnaeus

Hillers Manual of Trees and Shrubs

http://www.tropicos.org/Name/27101612

Clematis by Christopher Lloyd

The Well-Tempered Garden by Christopher Lloyd

Walling Materials

Brick wall detail at Lartington Hall
Brick wall detail

Historically walls have tended to be built from the nearest suitable materials and this has to very individual regional building styles. Since the advent of modern mass transport this has begun to be broken down; except where local planning restrictions have protected it. That is not to say the local traditional building style has to be followed slavishly, if any is discernible in the first place, as often the use of a contrasting material can be very effective. Making a clear demarcation between the old and new; always fair better than a poor match.

Traditionally walls have been associated with bricks or stone pieces with a mortar between them to stabilise the structure. As a building technology this is a very old one; and was well established by the time the Romans combined this with the arch allowing them to create their major engineering feats. The individual units that create a wall tend to be small, partly from practical considerations and partly from aesthetic ones. The small individual units imparts great flexibility into any design for a wall, allowing the same wall to be both straight and curved at different points. Its appearance can also be uniform if the same material is used throughout or broken up if the sizes and/or colours of the materials are varied.

Walls though don’t have to be brick or stone; the material used for their construction is only limited by the designer’s imagination. Concrete, timber, recycled bottles and wire cages filled with cobbles have all been used to make walls. The choice of materials dramatically alters the effect wall will have within the garden, as will its detailing and height.

When choosing the material to build a wall the range of possibilities is vast, with hundreds of different bricks alone to consider. When deciding on a walling material a number of factors have to be taken into consideration:

What materials have already been used?

How much are you prepared to spend on the wall?

What is the danger of frost damage?

How solid does it need to be visually?

How high does it need to be?

What if anything does it have to support?

How important is it to the appearance of the garden?

What finished appearance is wanted?

What shape is it going to be?

What is the purpose of the wall?

While this list won’t make the selection for you; it will narrow down the search, help focus your mind and hopefully broaden your mind to less obvious possibilities.

What is a species

The idea of a species is fundamental to gardening and botany, but what is a species? A dictionary will give you a definition but not one which allows you to say this group of plants forms a species, as opposed to say a subspecies. The Cambridge Illustrated Glossary of Botanical Terms describes a species as,

A group of closely related, mutually fertile individuals, showing constant differences from allied groups, the basic unit of classification

 

As it is this is a nice definition but does really tie down what a species actually is? No, the truth is a species is indefinable. I realise this is probably about as helpful as a fridge in an igloo but once you appreciate what a species actually is it makes complete sense.

So how did we end up in this situation? Well, if anyone is to blame its probably Charles Darwin and Alfred Russel Wallace. These two men independently came to the same conclusion, though they both arrived at it from observing the plants and animals on small islands.

Prior to this people saw species as distinct groups:

 

A figure illustrating 3 species
What is a species – figure 1

 

The problem with this was two fold. One where did the species come from originally and second where did the fossils come from people kept finding. The fossils were clearly very old: some similar to living things, while others where very different but still recognisable as plants or animals with characteristics at least similar to living examples.

 

A figure illustrating 3 species and 2 fossils.
What is a species – figure 2

By the 1850’s when Darwin first published his ideas on the origin of species the notion that living things appeared by evolution was widely accepted but the mechanism which made it work was unknown. What Darwin and Russel suggested was that species changed into new ones by a very gradual, survival driven, process of small changes. Each step in this evolution is so small as to be unnoticeable at the time and could only be appreciated with the benefit of hindsight. This process applied to all the species all of the time; but over many years and generations. The only reason we see separate species is because all of these intermediates have been lost, except for the very rare fossil.

 

A figure illustrating the evolutionary relationship between 3 species and 2 fossils.
What is a species – figure 3

 

If this is correct, and all the evidence we have found to date supports this, then there is no real starting point to a species and the only end point can be extinction. What we call a species is merely the extant remnants in a chain of gradual changes.

For this reason a species is rather like fog, you can see where it is, you can say you are in it or not, but it’s impossible to say exactly where it stops and starts. This is why no one has yet come up with a strict definition of what a species is, and in all likelihood they never will.

 

Castanea sativa

Castanea sativa
Castanea sativa

The Sweet (or Spanish) Chestnut (Castanea sativa Mill.) is probably most know for its edible nuts, traditionally eaten around Christmas time, but in fact it makes a very fine large tree. Clothed in thick glossy leaves, tolerant of a wide range of soil types and relatively free of disease it has been extensively planted through the British Isles. Its quick growth and large size limits its use in all but the largest gardens when grown as a tree, but its success as a coppiced tree would allow the more ornamental forms to be more wildly grown. At present these are not widely grown but Castanea saliva ‘Albomarginata’ is a very attractive form with creamy white edged leaves and C. ‘ Aspleniifolia’ is a vary rare form with the serrated edges of the leaves drawn out into fine filaments.

Castanea sativa 'Albomarginata' foliage
Castanea sativa ‘Albomarginata’ foliage

It is believed that the tree was introduced by the Romans who ate the nuts but in practice the tree fails to provide a crop of edible nuts in all but the warmest parts of the UK. Globally though about 500,000 tonnes of chestnuts are produced annually, about half in the Far East. In France the best nuts are sold as marron and in Italy marron may refer to a cultivar of C. sativa which yields fewer high quality nuts. Though Castanea is only represented by C. sativa in cultivation in the UK the genus is quiet large and widely distributed with several hybrids and cultivars being actively studied because of its economic importance. Of lesser importance is the timber of Castanea due to its tendency to warp and split but its durability in contact with water has long been known and has made it a preferred wood for stakes.

Castanea sativa foliage and youing fruits
Castanea sativa foliage and youing fruits

Its scientific name dates from the 8th edition of Philip Miller’s Gardener’s Dictionary published in 1768 when he updated it to bring it into line with the Linnaeus system of plant names. He did though take the sweet chestnut back out of the beech genus, that Linnaeus had merged it into, arguing that the male catkins of Castanea are long and those of beech are globular. Castanea is Latin for chestnut while sativa comes from the Latin for cultivated. It is claimed that castanea itself comes from the Greek κάστανα meaning chestnut and a large number of Greek words where borrowed by Latin.

Castanea sativa bark
Castanea sativa bark

References:

Species Plantarum by Carl Linnaeus

Hillers Manual of Trees and Shrubs

Excursion flora of the British Isles by Clapham et al

Inventory of Chestnut Research, Germplasm And References, FAO http://www.fao.org/DOCREP/006/AD235E/AD235E00.HTM [accessed 30th January 2013]

http://apps.kew.org/trees/?page_id=85 [accessed 30th January 2013]

The Royal Horticultural Society Horticultural Database’, available at www.rhs.org.uk [accessed 30th January 2013]

Botanical Latin by William T. Stearn

Tropicos, botanical information system at the Missouri Botanical Garden – www.tropicos.org [accessed 30th January 2013]

New Year – New Vegetable Plot

The arrival of the New Year inevitably starts you thinking about next summer’s vegetable crop and what to grow. This will of course be influenced by how much space you have available to grow food in and how keen a vegetable gardener you are. The vast majority of us only have so much space available, so compromises have as always have to be made.

For some people vegetable growing is a hobby; but for an increasing number of us it’s a way of using a bit of our garden to supplement our supply of food for the kitchen.  With this in mind, how are we going to gain the most benefit with the time and space available? The competing demands of work, children and family life are going to limit how much time we can realistically expect to spend on growing vegetables.

The next problem is where in the garden are you going to use and how much space can we spare. Everyone who uses the garden will have their own demands on the space available, growing flowers, playing football, sunbathing, eating out and so on. Whichever space is chosen it will have fit in with these competing demands and so its fair to say you are not going to be self sufficient in vegetables. So what are we going to chose to grow?

The first step must thinking what do we actually use in our cooking, lettuce may be easy to grow, but if no one in the house actually likes lettuce there is no point in wasting time growing it! The next step is what is practical, you may love asparagus but if you are going to move in a few years you will be gone by the time it starts cropping. Likewise if you are on stony, gravelly soil you are going to struggle to grow decent root crops such as carrots.

This should leave you with a list of possibilities. Now look down the list. What are you going to gain the most benefit from growing? In many cases just as good can be bought from the supermarket. Potatoes take a lot of space so are very unlikely to have the space to grow more than a fraction of your needs. If on the other hand you like green tomato chutney you are going to have to grow them yourself. Tomatoes are a good case in point, commercially grown tomatoes have the advantage that they are available all year round and they will only produce a small crop if grown outdoors in the UK, but the sad fact is the flavour of the varieties grown commercially is very poor.

By a process of elimination you will whittle your list down until you are left with what you can grow and will get some real benefit from. The collection you end up with may seem an eclectic mix, and in coming years you will adjust the range grown, but you should end up gaining some real value from a small corner of your garden.