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Even in cool temperate weather, microclimates within gardens can enable frost-sensitive plants such as tree ferns and Geranium maderense to be grown.
Temperature
There are two main aspects to consider – air temperature and soil temperature. Both of these are vital factors in determining the successful growth of plants. Almost all plants purchased from garden centres are now informatively labelled. There should be a maximum and minimum temperature given, between which the particular plant will do well. In some nurseries, stock is not always so well labelled, so don’t be afraid to ask someone who works at the nursery if any plant you want to buy fits in to the maximum and minimum temperatures in your garden.
Frost is a hazard and can put plants at great risk. A frost occurs when the temperature falls below o°C (32°F) on clear, still nights. Local weather stations measure the temperature 1.5m (2yd) above ground level, so if the forecast in your area is for a temperature of 4°C (39°F), the temperature of your plants at ground level could be close to freezing.
Severe frosts can damage or put at peril even hardy plants, but in general terms it is important to know when the danger of spring frosts is likely to be over in your area. It is only after this date that you should plant out tender plants and summer vegetables. If a frost is forecast, it is advisable that you protect any plants that you know to be at risk from such a low temperature (see here (#litres_trial_promo)).
You’ll often hear the term ‘frost pockets’ used by gardeners. Frost pockets are low-lying areas such as valleys and hollows where cold air (which is heavier than warm air) flows downhill, accumulates and causes frost. So if you live in a valley or hollow you should take extra care against frost.
Climate change: Almost all scientists now agree that the earth’s climate is changing. The effects of global warming are much debated and contentious, but there is widespread expert opinion agreeing that there will continue to be a general rise in temperature, with a resulting frequency of flooding and droughts, as well as other extreme weather conditions all over the world.
Global warming will deliver a mixed bag to us gardeners as milder winters will allow a greater number of tender species, such as citrus fruits, to be grown outdoors in temperate zones, as well as increased yields of many vegetables, fruit and flowers due to increasing levels of CO2, which plants absorb in photosynthesis. Problems will include an increase in pests and diseases as well as increased maintenance to cover the longer growing season, and certainly many species of plants will suffer or face extinction. As gardeners we are all in a position to make a positive difference to our environment simply by planting and caring for plants appropriate to our environment. Recycling organic matter, improving the soil and planting for wildlife are just a few of the ways we can start to redress the balance and help to heal a planet that is under stress.
Plants you can expect to see more of include olive (Olea europaea), ginger lilies (Hedychium), banana (Musa basjoo), Canary Island date palm (Phoenix canariensis) and century plant (Agave americana).
At present, this Agave americana might not survive an average temperate winter. However, with milder winters due to climate change, such plants will become more commonly seen. In the right conditions, and over 30 years, these plants can grow up to 2m (6ft) high.
Wind
When it is severe or continuous, wind can cause much physical damage to plants. The best way to protect your garden from wind is to create windbreaks. These are simply plantings of trees or hedging that will reduce the speed of the wind by taking the brunt of the wind themselves, thus ‘breaking’ the wind. Natural windbreaks are generally more successful than man-made ones. So, if you have an area of garden that is particularly exposed to the wind, you should consider planting a screen of trees or shrubs that themselves are wind resistant. Ask advice from your local garden centre as to which plants these would be for your area.
Hedges are the perfect barrier for providing shelter from wind within a garden.
Rainfall
Rainfall is an essential aspect of climate that provides the water for your plants to grow. In areas of low rainfall, irrigation schemes can be very effective, but even they still depend on rain falling at some time. Most of our gardens still receive the water that they need through regular rainfall. Unfortunately, rain does not fall at predictable intervals and in consistent quantities, so your plants need to be able to cope with this variability in rainfall. This can sometimes present two main problems:
Waterlogging of the soil, occurs with consistent heavy rain where drainage is poor.
Drought conditions, where rain is sparse over long periods and the soil has dried up and the ground has gone hard.
In both cases, action can be taken to improve matters. Drainage of waterlogged soil can be improved by the addition of coarse grit. Cultivation of the soil will further improve matters (see here (#ulink_a2003ab4-b79a-5406-854f-aecd9d2943d9)). If the problem is persistent, a more complex solution has to be found, such as installing underground drains. This is an area where professional help should be sought.
In dry soil conditions, the addition of organic matter will assist water retention, but generally a regular watering regime has to be undertaken to ensure that the soil is kept moist. If you have free-draining soil and persistently dry conditions, then you should choose plants that suit the conditions. Grasses and many plants from the Mediterranean region are suitable for dry conditions. There is always an answer for whatever the situation.
Plants for wet positions
Betula nigra (river birch)
Caltha palustris (giant marsh marigold)
Gunnera manicata
Ligularia ‘Gregynog Gold’
Lysichiton americanus (yellow skunk cabbage)
Matteuccia struthiopteris (ostrich fern)
Persicaria amplexicaulis (bistort)
Rheum palmatum ‘Atrosanguineum’ (Chinese rhubarb)
Rodgersia aesculifolia
Trollius europaeus (common European globeflower)
Humidity
Humidity is the amount of water vapour in the atmosphere. It is also affected by the moisture content of the soil. At one extreme, high humidity can encourage the growth of mould and fungal diseases, while a low humidity can increase the rate at which plants dry out and wilt. Low humidity can be improved in a garden by introducing water features and soaking all hard areas and soil, occasionally hosing down with water. Gardeners often refer to this as ‘damping down’. The opposite extreme to low humidity occurs mainly in rainforests, where plants adapt to these very particular conditions. Careful selection of moisture-loving plants is therefore important.
It is unlikely that you will have a perfect balance of all of these elements of climate in your garden, but a basic understanding of your local conditions will help enormously. Knowing that you can take some steps to work with the climate and not against it will help to improve your gardening results.
Euphorbia myrsinites naturally grows in exposed rocky places, and so is ideal for planting in a drystone wall.
Astilbes are moisture-loving plants and are best grown in partial shade.
Soil (#ulink_71095199-f4d7-54ab-af19-1e35e452329d)
Getting to grips with the stuff that you grow things in can save you a lot of wasted time and money. A plant adapted for boggy conditions will thrive in a heavy, clay soil with poor drainage. Planted in a well-drained, sandy soil, lavender will thrive just as it does in its native Mediterranean soil. Of course, you can contrive soil conditions by planting in containers or raised beds, but as it’s usually not possible to change your type of soil, it is essential that you understand what you have.
You don’t need a degree in chemistry to gain an understanding of the many different types of soil. Although you could spend many years learning about and specializing in soil types, the structure of the soil, the balance of nutrients in the soil and the constituent make-up of the soil, it just isn’t necessary when you start out in your gardening endeavours. Instead, a simple appreciation of soil types and their respective strengths and weaknesses will do to get you started.
What is soil?
Soil is the growing medium for your plants. From soil, your plants will draw their water and their nutrients. The soil provides a base in which the plant is physically supported too. The fact that soil can do all of this shows you just what an amazing natural material it is.
Some people are lucky enough to have a good soil for gardening that needs little in the way of support and improvement. Others are less fortunate and have a soil that needs to be enhanced by improving the structure of the soil by adding organic material, such as manure, and improving the nutritional value of the soil through the addition of fertilizers (see here (#litres_trial_promo)). The types of soil that you may encounter are shown opposite.
Rhododendrons and azaleas both grow best in a soil that has a low pH value, which is usually referred to as ‘acid soil’.
Soil types at a glance
Soil structure
Topsoil: This is the soil on the surface of your garden. It is the soil level that contains almost all of the organic matter that has been dug in to the soil or applied as a top dressing to the soil in autumn.
The topsoil is the most supportive and nutritious of the soil levels for your plants. It is from the topsoil that the plants will draw most of their moisture and nutrients. The depth of top soil will vary greatly from place to place. You are very lucky if you have two spade depths or more of top soil in your garden.
It is in the topsoil that almost all of the organisms and insects that live in the soil will be found. Many of these are beneficial to the soil. One of the gardener’s best friends is the earthworm, which plays such an important part in the incorporation of organic material into the soil. Through all its wriggling around, it is a tireless worker in aerating the soil, improving the drainage and providing ideal conditions for encouraging root growth in plants.
Some new gardens have little or no topsoil at all, and if this is the case it will need importing into the garden. Topsoil is not cheap, but be aware that if you find yourself in this situation, it is crucial you don’t stint on importing it. Any penny-pinching at this stage will come back to haunt you in the years to come! Existing topsoil can also be increased with the addition of generous quantities of organic matter (see here (#ulink_a2003ab4-b79a-5406-854f-aecd9d2943d9)).
Stephen Dalton/NHPA
Worms have been conditioning our planet’s soil for millions of years by recycling organic matter.
Subsoil: This is the level below the topsoil and it usually differs in colour from the topsoil. It is often lighter in colour. One reason for this is that none, or very little, of the applied organic material reaches down to this level. The subsoil will still contain nutrients from which your plants will benefit, but it will not be anywhere near as fertile as the topsoil.
If, when you are digging, you reach subsoil, stop! Do not incorporate subsoil into the topsoil. You will know you have reached subsoil not only with a change in colour, but also as this layer will be more densely packed than the topsoil. You will undoubtedly have worked hard to achieve your desired structure and quality of topsoil. It will not assist you to then integrate subsoil into this valuable mix.
KIM’S TIPS
It is likely that most people will have a soil that is a mixture of two or more of the basic types described on the previous page.
What I look for in a soil is a good open structure that is crumbly and with an evenly moist texture.
Even if you don’t start with an ideal soil, it is possible to work towards a more ideal one with perseverance and, of course, a little general knowledge. So whatever type of soil you have it is good to know that you can improve on it.
The properties and condition of soil are absolutely fundamental to the level of your success in the garden. Plants, like children, will respond well to good nourishment!
The pH value of your soil
Depending on what you intend to plant in the garden, it may be useful for you to know the pH of the soil. Some soils are naturally acid, and some soils are naturally alkaline. There are plants that will only grow in an acid soil and, conversely, there are plants that will only grow in an alkaline soil. However, this is looking at both extremes of a soil’s acidity or alkalinity. Local climate will give you a clue as to whether your soil is alkaline or acid. High rainfall areas often have acidic soils as the rain leaches out alkaline elements in the soil, whereas alkaline soils are typically found in low rainfall areas. Classic acid-loving plants include heather, camellia, rhododendron, pieris and hydrangea. Classic alkaline plants include lilac, clematis, wisteria, rosemary and ceanothus.
Soil can be tested to see how acid or alkaline it is. The test is known as a pH test. The pH value ranges on a scale of 1 to 14. A pH value of 1 is very acid and a pH value of 14 indicates that the soil is very alkaline. A value of 7 is regarded as neutral.
Testing your soil
If you wish or need to know the pH of your soil, you can buy a soil testing kit from your local gardening centre. They are simple and easy to use:
1 Mix a small amount of soil with a chemical solution in a test tube.
2 Shake the tube and the solution will change colour.
3 Match the resultant colour against a colour chart supplied in the kit. This will correspond to a pH value and tell you to what degree your soil is acid or alkaline. Neutral soil has a pH of 7; a lower number indicates an acidic soil and a higher number, an alkaline soil.
The best soil
It is generally accepted that a neutral to slightly acidic pH would be the most beneficial in order to grow the widest range of plants. So a pH value somewhere between 5 and 7 would be ideal.
Alkaline soils are a problem if you wish to grow rhododendrons and heathers as both of these species thrive in acidic soils. Alkaline soils are also problematic because of their high level of calcium. Calcium increases the rate of decomposition of organic material, making it necessary to add manure to the soil more often.
Rhododendrons are not difficult to grow, but they do require an acid soil to do well.
Lavender originates from the rocky terrain of the Mediterranean and manages well in dry, stony soil.
Improving and buying soil
The most important thing you can do to keep all the plants in your garden happy and healthy is to improve your garden soil. The best way to do this is to increase the amount of organic matter that it contains by adding your own garden compost or well-rotted farmyard or stable manure. This last needs to be at least a year old because fresh manure can actually kill plants.
Organic matter consists of the dead and decomposing remains of animal and plant life and gives better overall soil fertility. Among other things it provides nutrients for plants, improves drainage, and helps retain moisture in the soil. Garden compost, farm manure, leaf mould and spent mushroom compost, are just some of the more common sources of organic matter. Any of these are not only good for improving the soil, but they can be used as a mulch to conserve moisture and suppress weeds if spread generously across the surface of a bed. Over time, worms will incorporate the mulch into the soil below. Organic matter incorporated into clay soil in the autumn will open it out, allowing more freedom for the circulation of air and water, promoting healthy root growth. Digging organic matter into sandy soils in the autumn will improve water and nutrient retention by acting like a sponge. Incorporate it into the soil whenever possible. I also make good use of potting compost that has already been used for seasonal bedding plants, spreading it across the vegetable garden and lightly forking it in before sowing seeds.
If you are starting to tackle your garden for the first time, the more you can do to improve your soil before planting the better. I have seen newly planted shrubs in poor, unimproved soil that, after a couple of growing seasons, have hardly made any growth at all. In soil that has had plenty of organic matter to bulk it up, the same shrubs would be almost mature in the same time.
The soil in our garden was originally poor, dry and free draining; I have selected plants that are suitable for this type of soil but I also continually improve the soil.
It is hard work though! When you finally manage to persuade your local farmer or stable owner to deliver you a load of well-rotted manure you will suddenly realize that it’s heavy, and it takes a lot of effort to move it all around the garden! But once the job is done, you can sit back, safe in the knowledge that the worms will get to work on it, pulling it down into the soil, and eventually the organic mulch will add nutrients and structure to the soil.
KIM’S TIPS
Plants are only as good as the soil that they grow in, so develop a regular habit of making your own compost, and enriching your soil with it whenever possible.
If well-rotted manure isn’t available from a local farm, you can buy or order it at garden centres.
Buying top soil
If you are redesigning your garden, or if your existing soil is very poor, you may decide that you need to bring in some extra topsoil. The quality of topsoil for sale can vary a lot, so it’s always best to look at it before buying it. Ideally the soil should be dark – humus rich – crumbly and free from stones and perennial weeds. Also get some advice on how much you need for any particular space – a couple of tonnes may sound a lot, but when it is spread out it doesn’t go that far.
• If you need a lot of soil to increase ground levels in a garden area, an average quality of soil will be okay. You can then incorporate organic matter into the top layer to improve the quality further.
• If you just need a small amount of topsoil for a planting layer over existing poorer soil, it’s really best to buy a more expensive ‘screened’ grade of soil. Screened soil has been sieved to remove stones and also any rubbish and most weeds.
It is also worth contacting your local council as many of them now operate a composting scheme where garden waste, cardboard and other biodegradable materials are collected from designated household bins and are composted on a massive scale. The resulting compost produced from these recycled materials makes an excellent soil conditioner and can save the need for buying large quantities of topsoil – and help the environment at the same time.
Incorporating organic matter into soil greatly benefits the whole garden, not just raised vegetable beds.
Basic botany (#ulink_f188d9bf-f43c-5d0b-ba83-c099fd2fde51)
Plants play the most important role in the cycle of life on our planet. Without plants, there would be no human or animal life on Earth. It is believed that millions of years ago, algae that grew in the planet’s seas somehow triggered the evolution of land living plants. These then in turn provided food for land-living animals as they evolved.
The oxygen we breathe also comes from plants as a byproduct of photosynthesis, which is the way a plant makes food for itself, and as part of this process plants also produce oxygen.
Leaves are the main food-making part of most plants. Chlorophyll is the green part of the leaves and captures energy from the sun. Using carbon dioxide and water, the leaves produce food in the form of sugars and starches, which provide the plant with energy to grow. Plants take in the carbon dioxide through tiny holes in their leaves, just like the pores in our skin, and oxygen is released as a by-product of photosynthesis through these tiny holes.
The plants also take in the water they need through their roots and lose water again through the tiny holes in their leaves. This process of taking in water and releasing it again is called transpiration.
For millions of years, the plants that existed on our planet were very simple in form and did not even produce what we think of as seeds. These early plants included tree ferns, horsetails, mosses and some conifers. They produced spores to reproduce, rather than flowers and seeds. Indeed, we still refer to them today as ‘non-flowering plants’.
Evolution eventually produced flowering plants that could spread themselves over greater distances by the dispersal of seeds. Through evolution, plants adapted to individual conditions, and it is estimated there are now over 260,000 species of plants identified.
Mosses and conifers were some of the earliest plants and so didn’t reproduce through flowers.
Evolution has created plants with specialist features such as hairs to protect the leaves from extremes of heat Some plants, such as cactus, have developed fleshy leaves to store water during periods of drought.
There is now an incredible variety within the plant kingdom, from plants such as tiny alpines to the world’s tallest living tree, a ‘coast redwood’ tree in California, which is over 112m (367ft) tall. The climate of different world regions also determines what types of plants can flourish there. Plants have adapted themselves gradually to enormous differences of climate and growing conditions throughout the world. It is not enough to just survive in some extreme conditions: plants need to flourish and propagate themselves too.
In regions of very low rainfall, plants like the cactus have developed water-storing tissue in their leaves and stems. Mediterranean plants have adapted to their environment by developing hairy or furry and also narrow or silvery leaves to protect themselves from extreme heat and drying winds and also to reduce transpiration as much as possible. Garden plants such as rock rose (Cistus), rosemary (Rosmarinus), lavender (Lavandula) and sage (Salvia) all come from this region, so they are perfect plants for a hot, exposed area in the garden. For shady, damp conditions, look for large, dark green leaves, such as hostas, which have adapted to maximize the amount of light that is received.
Pollination and seed production
Although plants have developed many ingenious ways of reproducing themselves, the most common is through cross pollination. This is where pollen from one plant is transferred to another to fertilize it. Most plants have flowers with the male and female parts present in each flower. However, they still need to be cross-pollinated with another flower. Many plants rely on insects, such as bees or butterflies, to transfer the pollen from one flower to another. Pollen is a useful source of protein for some insects, such as bees.
Insects are attracted to the flower by scent, colour and nectar. They are not deliberately pollinating flowers, but they are usually feeding on sugary liquid nectar produced by the flowers when the pollen is rubbed off the body of the insect. They carry pollen from flower to flower, while collecting nectar and pollen for themselves. After pollination, the plant produces a seed, which mostly grows protected inside the plant.
It’s not always insects that pollinate the flowers. Plants may use the wind, birds or even bats as pollinators. With wind-pollinated plants – such as grasses, cereals and some trees – the flowers are very simple, with no bright colours or pleasant scent as they don’t need to attract the insects. These plants have both male and female reproductive parts and they make a lot of pollen.
