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The greenhouse is one of the most useful tools a gardener can have. It is a place to propagate seedlings, nurture young plants, experiment with exotic planting and hide from the rain. This book provides all the information and advice you will need to decide which greenhouse is right for you, set it up and get your planting going, and all under the watchful eye of the nation’s favourite gardener.

Includes:
* guidance on selecting, installing and maintaining a greenhouse
* recommended vegetables, fruit, herbs and ornamental plants for growing under cover
* practical advice on general care, harvesting, storage, propagation and pest control
* seasonal management guide
* step-by-step illustrations showing essential techniques

Alan Titchmarsh imparts a lifetime of expertise in these definitive guides for beginners and experienced gardeners. Step-by-step illustrations and easy-to-follow instructions guide you through the basic gardening skills and on to the advanced techniques, providing everything you need to get the most from your greenhouse.

About the Author

Originally trained at Hertfordshire College of Horticulture and Royal Botanic Gardens, Kew, Alan Titchmarsh is the author of over 40 books about gardening, including How to be a Gardener Book 1: Back to Basics, the fastest-selling of all time in the genre, and the bestselling The Kitchen Gardener: How to Grow Your Own Fruit and Veg. He writes for BBC Gardeners’ World Magazine, and is gardening correspondent for the Daily Express and Sunday Express. He has presented Gardeners’ World, the annual coverage of The Chelsea Flower Show and Nature of Britain, and has his own daily chatshow and presents his own show on Radio 2.

This ebook is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorized distribution or use of this text may be a direct infringement of the author’s and publisher’s rights and those responsible may be liable in law accordingly.

Published in 2010 by BBC Books, an imprint of Ebury Publishing, a Random House Group Company

The right of Alan Titchmarsh to be identified as the author of this work has been asserted in accordance with Sections 77 and 78 of the Copyright, Designs and Patents Act 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner.

Addresses for companies within the Random House Group can be found at www.randomhouse.co.uk

Introduction

Gardening is one of the best and most fulfilling activities on earth, but it can sometimes seem complicated and confusing. The answers to problems can usually be found in books, but big fat gardening books can be rather daunting. Where do you start? How can you find just the information you want without wading through lots of stuff that is not appropriate to your particular problem? Well, a good index is helpful, but sometimes a smaller book devoted to one particular subject fits the bill better – especially if it is reasonably priced and if you have a small garden where you might not be able to fit in everything suggested in a larger volume.

The How to Garden books aim to fill that gap – even if sometimes it may be only a small one. They are clearly set out and written, I hope, in a straightforward, easy-to-understand style. I don’t see any point in making gardening complicated, when much of it is based on common sense and observation. (All the key techniques are explained and illustrated, and I’ve included plenty of tips and tricks of the trade.)

There are suggestions on the best plants and the best varieties to grow in particular situations and for a particular effect. I’ve tried to keep the information crisp and to the point so that you can find what you need quickly and easily and then put your new-found knowledge into practice. Don’t worry if you’re not familiar with the Latin names of plants. They are there to make sure you can find the plant as it will be labelled in the nursery or garden centre, but where appropriate I have included common names, too. Forgetting a plant’s name need not stand in your way when it comes to being able to grow it.

Above all, the How to Garden books are designed to fill you with passion and enthusiasm for your garden and all that its creation and care entails, from designing and planting it to maintaining it and enjoying it. For more than fifty years gardening has been my passion, and that initial enthusiasm for watching plants grow, for trying something new and for just being outside pottering has never faded. If anything I am keener on gardening now than I ever was and get more satisfaction from my plants every day. It’s not that I am simply a romantic, but rather that I have learned to look for the good in gardens and in plants, and there is lots to be found. Oh, there are times when I fail – when my plants don’t grow as well as they should and I need to try harder. But where would I rather be on a sunny day? Nowhere!

The How to Garden handbooks will, I hope, allow some of that enthusiasm – childish though it may be – to rub off on you, and the information they contain will, I hope, make you a better gardener, as well as opening your eyes to the magic of plants and flowers.

What is a greenhouse?

A proper greenhouse is often seen as the mark of a serious gardener, but if you don’t consider yourself such, don’t be put off – gardening under glass is really no different from gardening outdoors, except you’ve got more control over the climate. Greenhouses have many benefits – how you use yours will depend on the type of plants you’d like to grow.

At its most straightforward, a greenhouse is a place where you can raise and grow plants that will not do so well outside. This may be because they are unable to cope with weather conditions at certain times of the year or because they do not like, or cannot survive, your prevailing weather conditions all year. Greenhouses also make excellent plant nurseries, where you can plant seeds, raise cuttings and generally manage and increase your stock of plants.

Added protection

Many popular vegetable plants are sensitive to cold weather and benefit from being started in a greenhouse. For example, sweetcorn needs a long growing season, but it does not like the cold, wet weather of early spring. So you plant the seeds in pots under cover, and the seedlings grow away happily until late spring, when conditions are such that they will survive outside.

Other vegetable plants, such as tomatoes, chillies, cucumbers and aubergines, are also best sown under cover to be planted out in late spring and early summer, or kept indoors for their whole lives. For these, the benefit of growing indoors is mostly the warmth, but they are also protected from wind and rain, which means plants and crops are less likely to be damaged, and the result is higher yields.

What about the plants that are never able to cope with prevailing weather conditions? These are usually the ones that come from habitats and homelands very different from our own. They include plants as diverse as orchids, many of which need continuous warmth and high humidity in order to survive, and alpines, which prefer cool, dryish conditions and dislike water on their leaves in winter, so need protection from rain. There are also plenty of others, including cacti and tropical plants of the sort that are often grown as house plants. Although these survive in our houses, that is often all they do. They can be transformed into things of real beauty when they are grown in a greenhouse, bursting into bloom in the more natural light levels and temperatures.

A plant nursery

If you’re keen on growing plants from scratch, a greenhouse is almost indispensable. You can use it as a potting shed as well as a nursery and set it up to provide perfect conditions for raising new plants. You can install electricity in the greenhouse and provide heated propagators for those seeds or cuttings that need them, but others will simply benefit from the extra protection from predators, such as slugs or mice, and extremes of the weather. Thinning, pricking out and potting up are all easier done in one place, too.

Depending on how well organized you are, and how you have arranged your garden, you can also use a greenhouse as a staging post for indoor flowering plants. Keep up a continuous display in your house by bringing on the different plants in the greenhouse until they’re ready to bloom, then moving them into prime position in the house, porch or conservatory. Once their moment of glory is over, you have a suitable place for your plants to recuperate.

Greenhouse temperatures

Greenhouses are usually described as either unheated, cool, warm or hot, terms with fairly specific meanings. For more information on heating and insulation, see here.

An unheated greenhouse is the most economical type, but also the most limited. Providing some heat in early spring and in autumn widens the range of plants that you can grow. It also increases your yields of vegetables, such as tomatoes and cucumbers, and extends your cropping season with salad plants, for instance. However, if you really want to make the most of your greenhouse, consider year-round heating; if you want to grow tender or tropical ornamentals, it is an essential requirement.

A cool house is kept at a minimum of 7°C (45°F) through the winter. This is pretty much the lowest temperature that most tender plants, such as citrus fruit, pelargoniums and ornamental bananas, will withstand. Any lower and you need to consider covering plants with fleece during colder snaps.

A warm house kept at a minimum of 13°C (55°F) suits tropical plants such as amaryllis (Hippeastrum), Cape primroses (Streptocarpus), begonias, poinsettias (Euphorbia pulcherrima) and many orchids. However, it will be too warm for other less exotic plants.

A hot house, also called a stove house, is for the real specialist and has temperatures in excess of 18°C (65°F). This is the temperature you will need for some orchids, tender flowering plants like stephanotis and gloxinia (Sinningia), and even a range of leafy ornamentals including coleus (Solenostemon).

Anatomy of a greenhouse

Greenhouses are fairly simple structures – particularly the basic aluminium types, which are the most common. However, the details are a little more complex. It pays to understand the ‘anatomy’ of a greenhouse before you buy, so you can be certain of making the right choice. Most greenhouses do the same basic job and have much the same components, but elements such as the door, the vents, the roof height and so on will all make a surprising difference to how easy they are to use and maintain.

Frame Greenhouses have various braces and cross bars that work together to support the glass. Individually they are not very strong, particularly aluminium ones, so each must be properly fitted and the nuts checked and tightened regularly.

Door A sliding door is best, since you can leave it open for ventilation without fear of it slamming. It also takes up minimal space – a bonus in a small garden. Doorways need to be at least 90cm (3ft) wide, and even wider if you want to bring a wheelbarrow into the greenhouse.

Base Often an optional extra, this raises glass panels off the ground and provides a foundation. However, it is worth considering installing a course of bricks for extra strength as well, particularly if you’re placing the greenhouse onto soil (see here).

Glass panels These are usually a combination of standard sizes. Very large panels are more expensive to replace if they break, so opt for smaller ones if the cost may be a problem.

Side vents You need at least a couple of these for air circulation. They are often louvres, which don’t stick out so far as a fully hinged pane when open and are less likely to get knocked as you walk around the greenhouse, but are more difficult to shut firmly against the cold.

Roof vents These usually open up and outwards and allow heat to escape, as well as increasing air circulation. The ideal is to have one or two on both sides of the roof, equal in total area to around about one sixth of the floor space.

Kicking panels These can go all the way around the house or just be on the door. They keep feet away from glass and are an important safety consideration.

Guttering and water butts The environmentally conscious gardener will want to have guttering to catch rainwater, and substantial water butts to store it in.

Greenhouse design

Nowadays, greenhouses come in an extremely wide range of shapes and sizes and their frames are made from a variety of materials. Depending on your tastes, your budget and the space available, you can choose anything from the standard utilitarian aluminium type of greenhouse to a fancy reproduction Victorian glasshouse, complete with finials and maybe even a weathervane. Most types will do more or less the same job, but they vary greatly in their price, ease of use and maintenance requirements.

Shape

One of the first considerations to take into account when you are choosing a greenhouse is shape. Although it might seem important only from an aesthetic point of view, shape also has an impact on useability.

Basic greenhouse shapes

When it comes to choosing a greenhouse, think about the pros and cons of each style. The span greenhouse is practical and versatile, but the sides of a Dutch light let more light in at the base. A half-span or lean-to is useful in confined spaces and for particular plants, and a polygon often suits the smaller garden. Half-walling provides added insulation.

SPAN

SPAN WITH HALF-WALL

HALF-SPAN OR LEAN-TO

LEAN-TO WITH CURVED ROOF

DUTCH LIGHT

POLYGONAL

Span and lean-to

There is a reason why the most common type of greenhouse is what is called the span greenhouse (see here) – rectangular with straight sides and a pitched roof. This shape provides plenty of growing space along each side, with the plants exposed to the maximum amount of light, while still being easy for someone standing in the middle of the greenhouse to work. A pitched roof provides height, particularly in the centre, where you are likely to be standing, and also contributes to the stability and overall strength of the structure.

Spans are freestanding, but you can get a three-quarter span or even a half-span or lean-to if space is limited (see here). Again, these are very practical buildings with a good balance of growing space and working space. However, they tend to be more expensive, and they need to be built against a wall or fence, which makes them more complicated to install. If installing one against the wall of your house, you could fit a communicating door and consider extending your central heating into the greenhouse. Walls and fences are also very useful for erecting shelving, and make a good site for climbing plants.

Dutch light

A Dutch light greenhouse (see here) has walls that slope slightly, which allows more light in at the base, increasing the warmth and making the structure more stable. This makes Dutch lights good for raising low-growing plants in soil borders, but the sloping sides do complicate plant supports and the larger panels can be expensive to buy and replace if they are glass.

Dome-shaped

Dome-shaped greenhouses or ‘biomes’ (see here) have recently become popular again. The shape ensures that several panes are at right angles to the sun throughout the day, which maximizes the light inside. Domes are attractive but pricey. They are sometimes not as practical for growing tall plants as the more traditional shapes, and will not accommodate standard shelves, benches and other fittings.

Curved roof

Some greenhouses, including lean-tos, have a curved roof (see here). This allows in more light and also looks slightly less utilitarian than standard models, but curved types are more costly to buy and to replace. The roof isn’t truly curved; each row of panes is set at a slight angle to the last, so the effect is of a curve. Freestanding greenhouses with curved walls are also available but are less common.

Polygonal

Many-sided greenhouses look more decorative than rectangular ones, and are a good choice where space in the garden is limited, where you want only a small amount of indoor space, or where you really want a greenhouse that looks good from the outside as well as being functional. At their most simple, they are usually octagonal with a sloping roof (see here), but you can get them with more sides or, if price is not a problem, in more fanciful designs – such as miniature pagodas.

Polygonal greenhouses are not as practical to use as rectangular ones: you will be cramped when bending down to tend plants on the ground, but if you put them on benches at waist height, there is a lot of wasted space underneath them. However, they allow in plenty of light and can grow a range of plants reasonably well; they are particularly good for displaying plant collections.

Size

It’s important to get a greenhouse of a size that will make it enjoyable and practical to use, as well as looking good in its surroundings. One of the most commonly cited ways of deciding on a size is to go for one that is bigger than you think you will need. The wonderfully positive thinking behind this is that as soon as you start using it, you’ll find many more uses for it than you ever imagined, and if you get a small one, you’ll wish it was bigger. However, there are some rather more practical ways to help you make up your mind.

First, measure out the area that you have available. Allow for access around all four sides of the greenhouse – 1.5m (5ft) is ideal, although 1.2m (4ft) is workable at a pinch. Think about how you’re going to use the space. For example, if you’re planning to manoeuvre wheelbarrows and lawnmowers, you’ll need more room than if you simply want to be able to walk around it to clean the glass from time to time. (For more on siting your greenhouse, see here.)

Next, you need to think about height. To enjoy working in your greenhouse, you have to be able to move around it easily and stand up straight in most of it. A height of around 1.5m (5ft) at the eaves should give a height at the ridge of about 2.2m (7ft). If you’re short, you could have a slightly lower ridge, but this sort of height is the most practical and comfortable to work in. Taller greenhouses allow more light in, too, as well as providing room for taller plants.

On a budget?

Although they may be tempting because of their very low price, beware of the very cheap mini-greenhouses that consist of lightweight tubular frames with polythene sheet covers. While reasonably useful for propagating plants in a very sheltered corner of the garden, they are often awkward to use and rarely spacious enough for the job. They are also insubstantial and prone to being blown over in windy weather, taking your precious plants with them.

Don’t forget

Glass-glazed greenhouses are potentially hazardous – you don’t want to be squeezing past them on a regular basis – so allow plenty of space around them and ensure good access.

Materials

There are two main choices of material: aluminium and wood. UPVC is another, more expensive, option for the greenhouse enthusiast.

Aluminium Since aluminium is light and comparatively strong, the frame can be quite slight, which means that it casts very little shade. It is also maintenance free – a big plus to a busy gardener. It usually comes unpainted as a silvery-grey colour, but coloured frames are available. The main drawback of aluminium is its flexibility. The struts of cheaper models are easily bent and damaged, which can weaken the structure. Look for plenty of cross braces and a generally sturdy overall frame. Add strengtheners if needed.

Wood This is a traditional material and is undeniably usually much more attractive than aluminium. Also, if you want to have half-walling for increased insulation, wood generally looks better and will do a better job than aluminium. Another advantage is that it is easier to attach custom-made shelving and plant supports to a wooden structure than to an aluminium one.

The main drawback of wood is that it will need maintenance, since greenhouses are damp and wood is very susceptible to the growth of algae and moulds. Fitting guttering will help, but you’ll need to carry out regular inspections and attend to rot as soon as it starts.

UPVC Greenhouses complete with double glazing are also available. Like aluminium, these are easy to look after. They are inevitably a bit more pricey, but are worth considering if you are really keen, particularly if you’re planning to grow hot-house plants.

Glazing options

One of the most important aspects of any greenhouse is its glazing. These illustrations show how much light each type lets in (indicated by a straight arrow) and how much heat escapes (a squiggly arrow).

SINGLE GLAZING
Allows in over 90 per cent of light, and is reasonably good at retaining heat.

DOUBLE GLAZING
This is a good insulator, but the two layers of glass transmit less light than single glazing.

TWIN-WALL POLYCARBONATE
Good at retaining heat. Allows 83 per cent of light through, but this reduces with age.

POLYTUNNEL SHEET
Light transmission is fair, but it clouds with age. Heat retention relies on a draughtproof structure.

Don’t forget

You can buy aluminium-framed greenhouses that look as though they are made of wood, but they are relatively expensive.

Glazing

Glass is the most widely used material for glazing greenhouses, but there several options available.

Glass Horticultural glass is thinner than normal glass and so allows light through more easily. If it is not damaged, glass lasts forever and is easy to install and keep clean. Double glazing is available and retains heat well, but a disadvantage, aside from cost, is that light is not transmitted so well through it.

Twin-wall polycarbonate This is a common and inexpensive form of glazing. It consists of two layers of plastic sheeting with air trapped between, which makes it a good insulator. It is light and strong, but lets less light through than glass – a problem that increases as it ages.

Acrylic This has similar properties to polycarbonate and its flexibility makes it popular for decorative detailing, such as curved eaves. However, it is brittle and tends to scratch and discolour with age.

Polythene sheet Used to glaze polytunnels, polythene is cheap and reasonably good at transmitting light and retaining heat, but generally deteriorates with age.

Choosing the right greenhouse

By now you should have enough information to make a sensible decision about which sort of greenhouse you need, its size and basic fittings. However, before you buy, it’s worth sitting down and making a list of your needs, and critically assessing the various greenhouses you like to see which ones most nearly meet them. Try to be open-minded and not allow your prejudices to influence you, at least not until you have exhausted all other options.

Assess your gardening

Ask yourself what you want a greenhouse for. If you simply want to raise a few bedding plants, you might do just as well with a heated propagator on a windowsill indoors and a couple of cold frames. But if you’re planning on being self-sufficient in vegetables, or if you have a huge collection of cacti that is about to take over your home, a greenhouse will certainly be very useful. A well-used greenhouse can become the hub of a garden, acting as a focus for all sorts of garden activities – if you’re a keen gardener, you certainly won’t regret buying one.

Think about your future

Before splashing out, it also pays to think about your long-term plans. Greenhouses are a comparatively expensive purchase, and it doesn’t make sense to buy one if you’re going to move house next year. Taking down and transporting a greenhouse is not the easiest or most enjoyable job in the world – that’s why you see those adverts for second-hand ones, saying ‘Buyer dismantles’. (That said, if you’re buying a second-hand one, it’s best to see it standing, so you can assess its condition and see what’s missing or broken.)

Checklist for choosing a greenhouse

Size – make sure it is adequate for your needs and ambitions.

Cost – find out exactly what is included in the price.

Functionality – make sure the greenhouse is up to the job.

Useability – check for vents, doors, kicking panels, guttering, and places to attach shelving and other items you will need inside.

Appearance – does it look good? There’s no point in buying a greenhouse if you don’t like the look of it.

Look for inspiration

Imitiation is the most sincere form of flattery, as they say, and when it comes to greenhouses, it’s certainly worth having a look at what other people have in their gardens. Visit flower shows, garden centres and gardens open under the National Gardens Scheme (also known as Yellow Book gardens), and ask your friends and fellow gardeners what they like and dislike about the model they’ve got. Gardeners are usually very willing to share information, and you’ll probably find out the pros and cons of all sorts of designs just by mentioning you’re interested.

Compare prices

Decide on a few likely models and find out what comes with them and what additional items you’ll need that will increase the overall cost. Some companies throw in shelving, extra vents, guttering, staging and so on. Have a look at what they offer – it might be a bargain, or it might be poor quality, in which case you’ll want to buy your own accessories elsewhere.

Consider the cheapest models, but do it with care as there are bound to be reasons why they’re inexpensive. It might pay to get the next price up, which could give you a sturdier, longer-lasting greenhouse that is a joy to use.

There are firms that will deliver and erect a greenhouse. This will inevitably add to the cost, but you have the security of knowing that they should deal with any little niggles, breakages and so on before leaving you with your new purchase. On the other hand, if you’re a perfectionist, or have your own ideas about how you want your greenhouse to be arranged, you might be happier putting it up yourself. Bear in mind that, unless you are buying a mini-greenhouse, this is not a one-person job.

Look for hidden costs

The price of the greenhouse is not the only cost to consider. Buying a greenhouse can lead to quite a few other expenses that you might not have bargained for. For example, if you want to install electricity and water, these will cost you, as will foundations and a path leading to and around the greenhouse. More obvious items include propagators, watering systems and automatic vent openers, all of which add to the utility of the greenhouse. Then there are blinds, heaters, thermometers, insulation – you could shop forever.

Don’t forget

Your other half. If there are two or more of you in the family who are keen on gardening, make sure you allow for everyone when you decide which type to buy. If you don’t, you might very well find your greenhouse being overrun by their activities anyway.

FOCUS ON Greenhouse alternatives

If for some reason, such as space or expense, you don’t want a greenhouse, but you like the idea of increasing the range of plants you can grow and the way you grow them, there are numerous other options. They range from a bright windowsill in the house that can double up as a propagator, to an ornamental conservatory, designed to be a place to display and grow plants as well as enjoy afternoon tea on cooler days.

Windowsills

Windowsills are the most readily available and cheapest form of plant propagators. A wide windowsill that gets plenty of light but not too much direct sunshine is very handy for raising seeds, and if it is spacious, it would also be suitable for growing tender herbs, such as basil, as well as a range of flowering house plants. If it is wide enough, you could stand a small heated propagator on it; otherwise plant seeds in trays and cover them with a sheet of glass or plastic until they germinate. The main drawback of windowsills is that all the light tends to come from only one direction. However, it is a simple job to turn plants around regularly so that they don’t end up leaning in one direction.

Conservatories

Conservatories can and do make excellent places for growing and displaying plants. However, they usually differ from greenhouses in some crucial ways, making them less suitable for the general growing and displaying of plants. They tend to contain soft furnishings and other household items, so watering must be done with care and damping down (see here) is rarely possible; they are often integral to the house so cannot be left open on hot days, which means the plants can suffer from heat stress; and many have special glazing to reduce glare for humans, which also reduces light levels for plants. On the plus side, conservatories are usually double glazed and heated, making them ideal for growing tropical plants.

If you’re considering installing a conservatory, you can make it more plant-friendly by fitting roof vents and a stone or tiled floor that can cope with water. However, if you’re really keen on your plants, it’s cheaper to have a rather larger greenhouse and put a couple of chairs in there than it is to build a conservatory, and there are plenty of very attractive greenhouses on the market.

Pick plants that like the conditions windowsills and conservatories offer and you should be able to have a colourful show all year round.

Porches

Depending on their design and situation, porches can make useful plant display areas, but they are less likely to be suitable for raising young plants. This is simply because they are intended to take through traffic, and all that coming and going will produce great temperature fluctuations as well as draughts and the risk of damage from passing bodies. A porch is also unlikely to be heated, in which case overnight temperatures may be very low. That said, if your porch is little used, bright, sheltered and generally warm, it is worth considering using it as a mini-greenhouse.

Mini-greenhouses

Greenhouses come in all shapes and sizes and even if you have a tiny garden, you can probably find a spot for a small greenhouse, whether it is a lean-to, octagon or mini. As long as it receives sun for most of the day, you will be able to grow things in it.

About the Book

About the Author

Introduction

What is a greenhouse?

Added protection

A plant nursery

Greenhouse temperatures

Anatomy of a greenhouse

Greenhouse design

Shape

Basic greenhouse shapes

Span and lean-to

Dutch light

Dome-shaped

Curved roof

Polygonal

Size

On a budget?

Don’t forget

Materials

Glazing options

Don’t forget

Glazing

Choosing the right greenhouse

Assess your gardening

Think about your future

Checklist for choosing a greenhouse

Look for inspiration

Compare prices

Look for hidden costs

Don’t forget

FOCUS ON Greenhouse alternatives

Windowsills

Conservatories

Porches

Mini-greenhouses