INTRODUCTION

This chapter will show that growing plants in protective structures can be enormously beneficial for commercial growers and gardeners who are producing crops all year round or trying to extend the growing season in the spring and autumn. These extra crops can attract premium prices for producers, an important factor for those whose cash flow is reduced during the winter months.

The positioning, building and management of any structure requires careful planning and preparation of the site in order to maximise the benefits and justify the additional costs involved compared to growing in the open ground.

Protective structures are made from many materials and constructed in many shapes and sizes: from the home-made polythene lean-to on an allotment, a cedar wood amateur greenhouse in a private garden to a modern, fully automated aluminium glasshouse covering many hectares. Polythene and netting tunnels, conservatories, cold frames and cloches are also considered as protected structures. What they all have in common is the ability to create an environment that induces improved plant growth compared to those growing in an open environment outside.

The uses for protective growing structures are varied. Many are used to produce edible crops grown direct in the ground or modern methods can be used where plants are grown in artificial growing media and have no contact with the soil such as hydroponic and nutrient film units.

Growers can use protected structures for a wide range of crops throughout the complete production cycle or for a specific growing period, such as propagation and establishing newly potted plants. Some houseplants and cut flower crops require carefully controlled light regimes to ensure they have colour and flower at a certain time in order to be saleable for a specific market; other plants require protection from the extremes of the weather to ensure they grow to the desired size and quality within strict time periods.

INTRODUCTION

The majority of plants may suffer with pests or disease outbreaks at some time or other. Integrated pest management (IPM) brings together all aspects of pest and disease control: initially using cultural techniques, biological control, environmental control and then finally selective pesticides as a backup. This has developed as a more sustainable method of pest and disease control, and as a pesticide-resistance management tool. The vast majority of UK-grown edible crops are produced within strict guidelines that have been developed between advisors, growers and the retail outlets (www.assuredproduce.co.uk). The non-governmental organisation GlobalG.A.P. (www.globalgap.org) sets voluntary standards for growth and production of many crops including edibles, ornamentals and livestock production. Both organisations specify the importance of using IPM techniques in crop production.

Controllable environmental conditions can influence pest and disease pressure by inhibiting plant pathogens and by providing more suitable conditions for biological control agents to work more effectively. Pesticide regulation in Europe and the impact due to loss of key active ingredients on agriculture and horticulture has recently been reviewed by Chandler (2008) with the conclusion that IPM should be at the centre of European Union (EU) crop protection policy.

INTRODUCTION

It is important to understand the structure and workings of plants if you are to grow them to their full potential. Knowledge about a plant’s life cycle indicates when it should be sown or planted, grown on and harvested, with each of the different categories named, defined and discussed, together with what treatments the plant may require to get the best from them, this knowledge includes their durability, economic use, and decorative or structural value.

Knowing about a plant’s external and internal structure and how they work is very useful for propagation, this leads on to such decisions as the type of material to use related to the time of year or the plant’s ability to produce adventitious roots on a wide range of different parts. A selection of species within a plant genus can have very different propagation and maintenance requirements. Also this information has a role to play in solving physiological problems that may occur with plants, especially those related to nutritional imbalances.

However, please note that there is still much to learn about the internal workings of plants and research is still ongoing. This greater and developing understanding will be useful in the future to help improve plant growth and yields to feed an ever-growing population. To aid in the gaining of this knowledge you will need to first develop a basic understanding of how plants grow, and hopefully this chapter will give you this introductory understanding.

INTRODUCTION

Within this section the direction is provided to start influencing the growing or display conditions for plants, that provide the best or quickest results. Leading on from the foundations, the opportunities are outlined and discussed for adjusting our thinking of how to obtain the maximum benefit from our present knowledge level and build on this to meet our objectives, whatever they may be.

One of the most pleasing aspects of gardening is the reward of new plants that are free apart from a little time and effort. Propagating plants vegetatively provides a plethora of methods, with the background reasons for the selected methods being discussed, together with the alternatives on offer. Technical language is fully explained and images are provided to enhance understanding of the practical aspects.

The whole subject of designing plants leads on from home propagational techniques into a world filled with a new language and some fears about the unknown, and worries as to the pathway of genetic modification being a one-way street or dead end to some species.

Shaping plants, as a topic, is always high on the agenda when plant people meet or undertake garden visits. The discussion runs from the ‘only prune to shape, once in a lifetime’ through to the ‘cut it to the ground, once a week, if not more often’ view, and everything in between. However, often the reasons and the methods that can be used are unknown or have been forgotten over time. Whereas, newer methods or techniques, such as the Chelsea chop, are being adjusted or renamed for modern times.

INTRODUCTION

Horticulturists throughout the ages have striven for plants that suit their needs: be they flower colour, odour, fruit size, shape, uniform harvest or resistance to pests and diseases. This chapter explains the biological processes that produce these characteristics (genetics and the inheritance of characteristics) and goes someway to explore the methods used by horticulturists in achieving a ‘designed’ plant. The techniques and morals of genetic engineering are explored in some detail, as this is an emotive and relatively modern technique of designing plants that is often cited in the media, commonly with some bias. It is important that you, as a student of horticulture, are informed of this technique and are able to make decisions of the validity of its use, for yourself, based upon a sound technical knowledge and understanding of the processes involved.

Genetics is, among other things, the study of the inheritance of characteristics. Characteristics may be observable, such as flower colour, shape or odour, or they may be ‘hidden’, such as the plant’s abilities of disease resistance or resilience to dry conditions, either naturally or in times of stress.

The way these characteristics are passed from one generation to another is by means of genes (it is, however, important to point out that the environment also has an effect on a plant’s characteristics although we will focus mainly on the genes’ role). Genes are lengths of DNA (deoxyribonucleic acid), a long string-like chemical that chromosomes are made from, and are located within the nucleus of cells.

INTRODUCTION

In the wild, the majority of higher plants reproduce by means of seeds. However, in the garden this is often not desirable, or may not be possible and other means must be used to obtain new plants. Therefore vegetative methods have been developed where a section of the parent plant is selected and roots are established so it can live independently.

A variety of different methods can be used to propagate plants vegetatively. These include softwood and hardwood cuttings, root cuttings, leaf cuttings, division, layering and a number of specialised techniques, such as grafting, budding and reproduction from structures such as bulbs and corms. The first section (Basic principles) is concerned with the physiological principles underlying the regeneration of new plants by vegetative propagation, with the second section (Practical techniques) focusing on the practicalities of the various procedures. Some techniques are very simple and success is guaranteed, while others require patience, skill, equipment and perfect timing. Micropropagation has become an important method for the regeneration of large numbers of plants by vegetative means and more details are given in the text below. Other methods are outlined with the time of year or age of the material highlighted. This allows a more informed view for the propagator to select a more suitable, potentially easier, method to be chosen with the aim of maximum success as the result. The environmental options available are also discussed, together with the required equipment, for all technical levels.

INTRODUCTION

The ‘feel good factor’ of good light levels is well known to humans with the pleasing emotional response to sunshine and the longer days of summer being welcomed after a long, dark winter.

However, green plants (all those with leaves or stems that contain chlorophyll) are completely dependent on light for many aspects of their growth and development. In particular, light energy is required to fuel the process of photosynthesis, which results in the production of carbohydrates and, subsequently, leads to all of the other organic components of plants. Light is also an important source of information for plants, giving them the ability to sense their light environment and, in many cases, also their seasonal environment.

This chapter describes how plants use light under different environmental conditions to ensure growth is continued to successfully complete their life cycles and set seed to provide future generations. The chapter also considers how gardeners can manage light most efficiently in the context of the garden, especially as climate change is likely to lead to altered seasonal light levels. The interrelationship of light with temperature and water availability leads on to future management and the opportunities presented with the balance between light and shade. Shade perception and plant adaptations to shade are also introduced to provide a greater understanding of this common, but somewhat challenging, environment.

INTRODUCTION

Why is it important for the reader to have a knowledge and understanding of flowers, fruits and seeds? First, the vast majority of the food we eat is produced from plants grown from seeds: including large-scale farming and vegetable production as well as ‘grow your own’ crops.

Having an understanding of flower parts and the types of inflorescence can help you to identify a plant. This chapter covers flower parts and structure, including the various types of inflorescence.

The function of flowers is to produce fruit and seed to perpetuate the species. The flower facilitates the pollination and fertilisation of the ovules that ensures the production of seed. Fertilisation results in the production of fruit, which ensures the survival and spread of the seed.

With the recent loss of pollinating insects, including bees, it is important to have a good understanding of pollination and fertilisation to ensure a good crop of fruit is produced. Factors affecting pollination and fertilisation and how the grower can improve these are discussed in this chapter.

Seeds also have the ability to survive very difficult climatic conditions that would kill many plants, thus the plant can survive over winter and grow again in the spring. A good understanding of seed germination requirements, overcoming dormancy and ensuring the correct conditions for growth helps to ensure a good crop. The germination process is explained along with the types of dormancy and how these control when the seed will germinate. Methods of breaking seed dormancy are also explained.

Finally, how to propagate plants from seed both indoors and outdoors and the various sowing techniques are covered.

INTRODUCTION

This chapter will show that commercial horticulture is a diverse and multidisciplinary global industry with thousands of commercial companies and organisations producing crops or offering their services to commercial customers, clients and retail consumers. These activities are carried out to satisfy local or regional demand, multinational operations or trading as vast global networks. These can vary from specialised plant growers to multiple retail chain stores; high street florist shops to seed producers and landscape contractors to tree surgeons, all supported by a wealth of research and development networks. With the world markets becoming more accessible and competitive it is essential that growers and suppliers are aware of how global issues will affect their existing customers and potential markets in the future. These factors could include fluctuating exchange rates within Europe or the sharp rise in global fuel prices, both dramatically affecting the supply and demand for crops. These variables can cause extreme difficulties for growers within an overcrowded, overstocked seasonal marketplace, especially where time-sensitive edible crops are being produced as any disruption in the supply chain will affect crop quality and its value. Many horticultural businesses can be divided into two main categories: those that sell their products or services to other commercial companies within the industry, these being wholesalers, and those that sell direct to consumers in retail nurseries, garden centres or multiple chain stores, these operate as retailers. There are companies that trade in two or more sectors, for example a wholesale production nursery supplying direct to its own onsite garden centre, or a landscape contractor growing plants for direct use in their private clients contracts.

Introduction

Conservation and sustainability go hand in hand and embrace all aspects of horticulture, from amenity to commercial and small to large scale. The gardener has a role to play whatever the size of garden. It is being increasingly recognised how important ordinary gardens are in providing a network of habitats for conserving wildlife and improving the environment.

Botanic gardens have long played a global role in conserving plant species, dating from the sixteenth century, with the first botanic garden in the UK being completed in 1663, in Oxford, (Oldfield, p. 13, 2007). This role is carried on today with traditional methods combined with the advantages of modern technology, for example at Kew’s Millennium Seedbank at Wakehurst Place, Sussex.

Many important charities have been founded to aid the conservation of plants and gardens, either as their main remit or as part of a wider theme of conservation and education, such as the National Trust and Plant Heritage. Legislation has played an increasingly important role, for example through the Wildlife and Countryside Act 1981, and Convention on International Trade in Endangered Species (CITES). Local planning authorities implement important planning legislation, for example, administering Tree Preservation Orders (TPOs).

Sustainable practices are fundamental to conservation. Again, these are important on all levels, from the compost heap and water butt in a back garden, to large-scale water storage for commercial nurseries and effective management of recycling in large parks and gardens.

Like other plants, trees have to engage in sex by proxy, using the wind, water or an animal as an intermediary to get pollen from one tree to another (see Box 5.1). Unlike many other plants, the sheer size of trees raises extra problems of pollination, and eventually seed dispersal, which are solved in ingenious ways. The original trees, the conifers, were (and still are) wind-pollinated. The flowering plants (angiosperms), which includes hardwood trees, evolved hand in hand with insects to be, not surprisingly, primarily insect-pollinated. Yet some have reverted to the old way of wind pollination, and for very good reasons. These are linked to geography: most trees in high latitudes are wind-pollinated, but animal pollination (insects, birds and mammals) becomes more important the closer one gets to the tropics, reaching 95% of trees around the equator. Figure 5.1 gives an overview of general flower structure.

Animal pollination

Animal pollination is primarily the world of the insect; in the wettest Costa Rican forests, for example, 90% of trees are insect pollinated. But within insect pollination there are different strategies. Some trees, like magnolias, apples, rowan (Sorbus aucuparia), European spindle (Euonymus europaea), some maples, hawthorns (Crataegus spp.) and a long list of others, go for quantity. They are generalists that spread the pollen on a wide range of flies and beetles in the hope that some will arrive on another flower of the same species. Common features are open flowers, often facing upwards, a drab colour, many stamens, easily reached nectar and a strong scent, especially at night (see Box 5.2 and Figure 5.2).