Post category: Trees and Shrubs

 

Shelter belts fulfill the same functions as hedges or screens, but on a larger scale. Very many large gardens, rural houses and farmyards would benefit from more shelter planting. Trees can be planted in blocks in corners or in a narrow belt.

 

Planting

 

The best shelter belts are porous enough to allow the wind through, but reduce its speed. Dense conifers are better mixed with deciduous trees because mixed shelter belts are better to look at, especially in winter when coniferous shelter can be depressingly dull.

Plant shelter belts across the direction of the wind that is to be slowed down, which is not always the prevailing wind direction. Where possible, plant two or more lines in a shelter belt, mixing at random a number of types such as hazel, hawthorn, holly, poplar, alder, pine, spruce, cypress, beech, larch and birch, choosing size and type as appropriate to the space available and the soil.

 

Spacing

 

In single rows, plant shelter trees about 1.5 metres apart. Space double rows about 1.2 metres apart and plant the trees about 2 metres apart in the rows. For multiple rows, space the rows about 1.5 metres apart and the trees 2.5 to 3 metres apart in the rows. Stagger the trees in each row.

Randomise the spacing of the trees in the rows and between the rows to achieve a more natural appearance. This is especially important when planting garden woodland blocks. The finished wood will look much more natural if the trees are not in exact rows.

 

Choosing trees

 

Choose deciduous native trees and Scots pine, which is given native status by some experts. Good trees for garden planting or close to house and buildings are the smaller ones, such as birch, hazel, holly and hawthorn. For damp ground, use willow and alder. Further from the house, the larger trees, such as oak and ash, can be used. Beech is not native but widely naturalized and Norway maple makes a fine tree for autumn colour. Sycamore is not native but very wind-resistant as is Scots pine and Monterey pine Wild cherry is a fine tree to include in small numbers for its fine spring flowering and rowan for autumn berries. Hornbeam is another non-native that is naturalized in places and very good on heavy land, where beech does badly. Small transplants of these species can be bought in forest nurseries.

 

After planting care of trees

 

Fence off shelter belts against grazing livestock, keeping trees at least 1.5 metres from the fence. Keep grass and weeds down for a few seasons with Roundup or similar. Give a little general fertiliser in the early years. If shelter becomes bare at the base as it gets older, try underplanting with common laurel.

 

While careful pruning enhances a tree or shrub, heavy cutting back usually spoils a plant’s shape, at least temporarily, but it might become necessary if a plant has outgrown its space. Before hard cutting back consider removing some shrubs or trees completely from a planting to allow room for the development of the remainder.

The best method of cutting back trees or shrubs is to reduce the number of branches. Completely remove, at source, half of the plant’s branches. Careful selection of the branches for removal will allow the plant to retain its shape. This thinning process may achieve enough size reduction. If not, shorten the remaining branches by one-third or half of their length.

Another method, for shrubs only, is to cut the plant right down to ground level. The cut stumps will sprout again and the shrub will regenerate itself. This rather drastic treatment should be carried out in April and may occasionally cause a shrub to die off.

To actually kill off tree stumps and prevent sprouting, paint the cut surfaces with Roundup. If the tree stem diameter is more than 10 centimetres, drill one hole for each 10 centimetres of diameter of the stump using a bit and brace and place some undiluted Roundup in the holes.

 

 

Diseases

 

Honey fungus, or bootlace fungus (Armillaria) is a widespread and serious root disease. Privet, griselinia, cypress, lilac, birch, willow and pine are very susceptible. The fungus grows in the roots just below the bark, producing white fluffy growth, black bootlace-like strings and yellow mushrooms.

 

 

Butt rot is a similar root disease of conifers, common near old shelter belts and forest plantations. There is no control. Remove stumps.

Phytophthora root rot has become a common disease since the advent of container-grown plants. Lawson’s cypress, rhododendron, heather, flowering cherry, yew, beech and lime are susceptible. The affected plants wilt and die slowly over a period of time, especially in summer. Avoid nurseries where there are dead and dying Lawson’s cypress.

Heart rots are diseases of the heart wood of large trees. Fungi enter the trunks through broken branches, and rot the heartwood. Brackets appear on the tree and release spores. Oak, beech, chestnut, ash, walnut and birch are often attacked and seriously weakened.

Silverleaf is a disease mainly of flowering cherry. The leaves on one or two branches go silvery and the tree eventually dies. Bacterial canker is another serious disease of the plum and cherry family, including laurel. Gum usually exudes from a main branch, and little holes (shot-hole) may appear in the leaves. The tree usually dies.

Die-back is a general name for the damage caused by a variety of fungi on small twigs and branches of many different trees and shrubs. Cut out dead shoots. Dutch elm disease is a very specific disease of elm that starts by killing a few small branches, and eventually the tree itself.

Leafspots and powdery mildew, caused by a variety of fungi, attack a wide range of trees and shrubs. These are usually harmless, if a plant is weakened, give it some fertiliser to speed recovery.

Fireblight affects apples, pears, cotoneaster, pyracantha, hawthorn, mountain-ash and Japanese quince. It first kills a few branches, these retaining their leaves as though scorched by fire. If suspected, notify the Dept. of Agriculture.

More detail on these in the section on Gardening techniques: Diseases

 

Pests 

 

A group of caterpillars on beech

 

Rabbits and hares cause very serious damage in rural areas. Fencing is the complete answer. Wrapping the stems of young trees with heavy polythene is effective too.

Greenflies feed off many trees and shrubs, especially honeysuckle, viburnum, privet, beech, lime, flowering cherry. Control is usually not necessary.

Caterpillars of many kinds eat the leaves of trees and shrubs, usually leaving holes. Damage is slight and control not necessary.

Leaf miners attack many trees, notably holly, leaving twisting tracks and blisters on the leaves. Though unsightly, control is not necessary.

Red spider mite attacks many trees and shrubs. Control is not necessary, except on dwarf spruces, which could lose all their leaves. Spray in April or May.

More detail on these in the section on Gardening techniques: Pests 

 

 

Sunken acid bed 

 

In areas where the soil is limy, an acid soil and peat bed is necessary to grow rhododendron, camellia, azalea, pernettya and other lime-haters. It can be of any size, even small enough for just one plant.

 

Rhododendrons need acid soil

 

Raised acid bed

 

A more simple approach, likely to be more successful, is to simply heap up the acid soil/peat mixture on the existing soil surface to a depth of about 25 centimetres. The sides can be retained by stones, turf sods or timber, or the heap can be graded back to the existing soil level.The acid soil and peat bed actually acidifies the soil beneath over a period of years. A raised bed is ideal for a grouping of lime-haters, but needs to be about two metres in diameter to be effective. Even one vigorous rhododendron would eventually fill an area of this size.Peat beds are prone to drying out because they are raised and they need watering at a rate of at least 70 litres per square metre per month in drought periods. Topping up with peat or well-rotted, organic material such as leaf mould should be carried out every two or three years. An application of sulphate of iron at up to 70 grams per square metre, and 30 grams of Epsom salts, if desired, can be made if the plants show signs of yellowing. Or use seqestered iron, available from garden centres.

 

Planting 

 

A hedge, or screen, is simply a line of trees or shrubs planted close together and trimmed to shape. Apart from providing shelter, privacy and boundaries, hedges can be used as a backdrop for the shape and colour of ornamental plants. A disadvantage is their tendency to draw moisture and nutrients from the surrounding soil. They cast shade too, and they often provide a haven for slugs and snails.

 

Small hedges can be very decorative

 

Spacing

 

Hedges planted at close spacing thicken up more quickly, but cost a bit more. Competition between the plants at closer spacing means they are more easily kept to the desired size. Most common hedges, including evergreens, are best planted 60 centimetres apart. Smaller types, such as berberis and hawthorn, should be planted at 40 centimetres apart.

 

Formal training

 

For a formal hedge, training should begin at planting, when the top 15 centimetres of the leading shoots are removed, which encourages the plants bush out lower down. Continue this tipping-back during the first two seasons and shorten strong side-shoots at the front and back of the hedge to keep the hedge narrow and encourage the plants to meet earlier.

Start clipping the sides first, to prevent the hedge becoming too wide. Clip the hedge to a wedge shape to let light get at the lower part. Otherwise the foliage dies and the bottom of the hedge goes bare.

 

Clipping

 

Regular clipping follows on the initial training period. Begin regular clipping before a hedge has reached its desired final size. Never let a hedge get beyond its ideal height and then, too late, try to bring it under control, particularly with cypresses. Stop the plants 30 centimetres short of the ideal height and let them reach it over five or six years, thickening up in the process.

 

Clip hedges to be narrower at the top

 

Informal hedges

 

For an informal hedge, such as forsythia or escallonia, and for tall screens, simply let the plants develop naturally for a couple of years. Then trim the sides with a secateurs, shortening all strong side-shoots. Flowering hedges should get this treatment after flowering. Avoid using hedge-clippers on informal hedges or screens if they are to have a natural informal appearance.

Another kind of informal hedge can be clipped to shape. In this case, the shape is informal, not the growth of the hedge. Unusual ‘cloud’ shapes, for instance, can be clipped into a hedge, even one that was formal to start with.

 

Overgrown hedges

 

Badly overgrown hedges can be cut back part-way, even right back close to the ground, and they will sprout again. Hedges that have become too broad can have one side cut off. The second side can be cut off, two years later, if desired. April is the month for these operations.

Cypress hedges cannot be cut back in this way, as they do not regenerate from bare wood. Never cut them back beyond the green part of the shoots or they will stay bare.

 

Many of the most popular garden trees are grafted on to rootstocks. Flowering cherry, flowering crab-apple, flowering hawthorn, mountain ash and whitebeam are examples. Any of these might produce suckers at ground level or at the top of the trunk – wherever the graft union is located.

 

Strong upright shoots may be coming from the rootstock

 

Suckers usually have small or coarse leaves and are more vigorous than the grafted variety. The young shoots should be removed as soon as they are noticed, or they will take over. They can be pulled or cut away, or chop them away with a spade if they are below soil. Firm the ground well to discourage further suckering.

A few other plants, although not grafted, produce suckers, for example stagshorn sumach, poplar, kerria and snowberry. These suckers arise from the roots of the tree or shrub and are the same plant.

If they arise from trees such as stagshorn sumach or poplar, they should be removed. If they arise from shrubs that naturally spread outwards by suckering, such as kerria or snowberry, they can be left in place if they are not a nuisance.

 

Young  deciduous trees

 

Pruning trees and shrubs can be quite complicated but there are a few general guidelines to consider. The only essential pruning is the removal of dead, damaged or diseased branches, and even this might not need to be carried out in a natural setting.

 

Trees have natural shape that should be preserved

 

Trees and shrubs generally do not need pruning. However, the shape of a tree, or the flowering display of a shrub, can be enhanced by pruning. Carefully observe the plant’s shape and discover its flowering time before attempting pruning.

 

Mature trees

 

Mature trees may need considerable pruning for safety reasons if large, heavy limbs pose a hazard. This dangerous and highly skilled work is best left to a qualified, fully insured tree surgeon.

If a small branch has to be removed, to let in light, for example, it should first be cut half way through on the underside, about 45 centimetres from the trunk. This cut prevents the branch tearing away the bark of the trunk. Next, cut through from the top. Finally, cut off the ‘snag’, leaving the all-important branch collar undamaged.

 

Conifers

 

Most conifers are best left unpruned because any pruning more light foliage trimming will tend to spoil their shape, which is the main reason for growing them. If they get too big for their position, take them out completely. ‘Topped’ conifers are an eyesore!

 

Shrubs

 

Flowering shrubs generally benefit from a little careful pruning. It helps to maintain a good display of flower and prevents the shrubs getting too big or too dense. The aim is to encourage the replacement of old shoots by new ones, removing the old ones completely, from where they arise on larger branches or from the ground.

 

Leave the branch collar intact when pruning

 

Prune spring and early summer flowering shrubs such as forsythia, flowering currant and philadelphus immediately after flowering. Shrubs that flower after the end of July should be pruned in March. These include hydrangea, hypericum and fuchsia.

Very many flowering shrubs need no pruning – rhododendron, camellia, pernettya, witch hazel and magnolia. These can have badly placed branches or over-long branches removed. Make sure that any pruning carried out is to a purpose.

The flowering shrubs that benefit are generally twiggy and bushy with many stems at ground level. Evergreen shrubs are grown for their foliage value and are not pruned usually but they can be reduced in size if necessary.

 

Plants can be trained, by means of tying-in and/or judicious pruning, to take a desired shape or to fill an allotted space. Climbing plants and wall shrubs such as pyracantha, cotoneaster and winter jasmine usually need to be trained, but a tree or shrub may also need to have its shape adjusted by tying in or by pruning.

 

Pyracantha needs to be tied in to wires

 

Where possible, tie in young shoots to the required position. On walls, use wires about 25 centimetres apart, fixed to brass screws or masonry nails driven into the wall. Wooden trellis makes an attractive support for climbing shrubs. Screw the trellis to wooden battens fixed with screws to the wall. If necessary, this allows the trellis to be easily taken down.

Use soft jute string, not plastic string, to tie in plants. The soft string breaks down and rots in a year or so and there is no danger of constricting the branches. Tie in the new shoots as they grow. If young shoots cannot be tied in to a suitable position, or if there are too many suitable shoots, prune out the surplus where they arise, during the summer.

 

Weeds can seriously impair the growth of young trees and shrubs by competing with them for moisture and nutrients. An area at least one metre diameter around young trees should be kept weed-free by hoeing carefully, by applying a layer of old carpet, a thick layer of cardboard, newspapers or organic mulch, or by using chemical weedkillers.

Mulching feeds the young tree and conserves moisture, as well as keeping weeds down. Some mulches, such as garden compost, grass clippings and farmyard manure, often contain weed seedlings and these will have to be controlled. Other mulching materials such as bark, brewer’s grains and mushroom compost are weed-free.

Chemical weed control is very successful but must be used properly. Contact weedkillers, such as Basta, will deal with grass and soft weeds. Soft weeds and tough perennial weeds can be spot-treated with Roundup. Brushwood Killer is useful for killing brambles and other scrub, including ivy.

As trees and shrubs get older, they can usually cope with weeds, being bigger and able to shade them out. Woody weeds such as brambles and elderberry can become a problem and should be dug out as soon as they are noticed. Other weeds such as bindweed might need to be spot-treated with Roundup.

 

To become really well established, young trees and shrubs should have access to plenty of plant nutrients for the first five or six years. On good, fertile soils, this feeding need only be a 5 centimetre layer of well-rotted manure or compost, topped up in April. This layer provides plant food and retains moisture in the soil. On poorer soils, 30 grams per square metre of general fertiliser or Tree and Shrub Fertiliser should also be applied, in spring.

 

Mulching feeds the plant and retains moisture

 

Be careful not to over-mulch on heavy soils because too much mulch can keep the soil wet and cold and restrict growth. Healthy balanced growth helps the plant to resist diseases and pests, and make an impact on the garden more quickly.

Older trees and shrubs need no fertiliser unless they look unhealthy and need a boost following pest or disease attack. Feeding as mentioned will encourage recovery. Established plants growing in poor hungry soil may fail to provide a good display of flowers or foliage and should be fed every year or every two years.

 

The water needs of trees and shrubs are quite often overlooked. Young, newly-planted trees are particularly vulnerable. For the first two summers after planting, any tree or shrub can suffer, especially conifers. During dry spells of more than one week, a close watch should be kept for signs of drought.

Plants showing signs of shortage should get a good watering – about 20 litres per plant, every ten days or so. Apart from obvious wilting, the danger signs are a listless appearance and dullness of leaf colour, especially with conifers. Even big established trees can come under moisture stress and might need to be watered, especially if they have had any root disturbance in recent years.

Root disturbance such as excavation, or a change in ground water level caused by building or roadworks, may result in small-sized leaves, sparsely held and even dead twigs. New growth sometimes appears on the main branches as the tree adapts by dying back from the top. A large shrub or small tree can be watered effectively by allowing a slight trickle of water from a hose to percolate down into the root zone over a period of a day or more. Move its position to deliver a very large quantity of water without waste. For a tree with a wide root area, a sprinkler could be used.

 

Trees and shrubs are sold either as container-grown plants or in the traditional way as field-grown, bare-root stock. Deciduous bare-root plants are planted from the beginning of November to the end of March. Evergreen bare-root plants are planted in October or April. Container-grown plants can be planted at any time of year, even in high summer. However, they establish best if planted during the traditional planting months.

Before planting, soak the roots of the plants in water. Allow container-grown plants to drain for a while afterwards. Make up a planting mix of moist peat with a handful of general fertiliser or Tree and Shrub Fertiliser added to each bucketful.

 

Make the planting hole wide enough

 

Completely remove any grass or weeds – spray with Roundup to kill existing weeds if necessary. Dig over the area where the planting hole will be, breaking down the soil lumps. 
Dig out the hole. When planting in a lawn area, place the removed soil on polythene sheeting to avoid messing up the grass.

Make the hole deep enough and wide enough to take the roots or rootball. Break up the soil in the bottom of the hole. Add a 5 centimetre layer of the planting mix and mix it with the soil in the bottom of the hole. Drive in a support stake at this stage, if a tree is being planted. A short stake is best unless the tree stem is tall and weak.

Place the plant in the hole and spread out the roots. Check that it is the same depth as it was previously planted – look for the soil mark on the stem. For container-grown, make the hole deep enough to leave the top of the compost just level with the soil surface. Be sure to avoid planting too deeply, which is a common cause of poor establishment.

 

 

Add some fine soil and planting mix. Work this in around the roots by giving the tree a little shake. Firm gently. Add more soil and firm again. Leave the soil surface neat. Water immediately after planting with about 10 litres of water per plant. If a stake is used, tie in the tree using two ties, one near the top and one half way down, unless a short stake is used, in which case one tie will be enough.

Be patient – do not expect results immediately after planting. Many shrubs take a few years before starting to flower. Although the shrub might be in flower at planting, or perhaps flowers in its first year, this flowering can be deceptive because it is caused by the restriction of the nursery container. When the tree roots gain the liberty of the open soil, the plant often skips flowering for a few seasons. Do not prune plants that have done this because it further delays flowing.

 

Guidelines 

 

How far apart and how many plants should occupy any particular piece of ground is a difficult question to answer. Much will depend on the eventual size and shape of the tree or shrub and its rate of growth. The rate of growth of trees and shrubs depends greatly on soil conditions and, to a considerable extent, it is a matter of taste and experience.

 

Shrubs filling their allotted space

 

Dense planting fills the space quickly, hiding the soil and helping to control weeds. But, planting at close spacing is expensive, because a greater number plants is used. After a while, trees and shrubs planted too closely together begin to interfere with each other’s development and they all end up spoiled.

 

Thinning out trees and shrubs

 

The spacing guidelines might give a planting that looks sparse, but this will not last long. To avoid an initial sparse look, over-planting and subsequent thinning might be carried out. Quick-growing shrubs can be used as colourful, but temporary, fillers. Broom, cistus, escallonia, weigela, ceanothus and lavatera are examples. Some of these are short-lived anyway, so thinning is almost automatic as they reach their lifespan and die out.

 

Planting may initially look a little bare

 

Specific spacing rules

 

When planting near boundary walls, keep large trees about three metres away and plant small trees and shrubs the height of the wall away. Plant wall shrubs and climbers between 15 centimetres and 45 centimetres away. When planting near a house, keep large trees at a distance equal to half their eventual height plus 6 metres. Plant small trees and large shrubs no closer then 3 metres, unless they are of narrow, columnar shape.

 

Size

 

Find out the eventual size of a tree or shrub before planting. It is a common mistake use trees or shrubs that are too large for the space available and these have to be removed or spoiled by heavy pruning. Use the larger plants to provide the framework – the backbone – of the planting and the smaller ones to complement and contrast with these larger plants. Generally, the tall plants are put to the back, the smaller ones to the front. An occasional exception might be made in order to provide contrast.

 

A variety of shapes used to good effect

 

Shape

 

Every tree and shrub has its individual shape. The main types of shape are columnar, conical, round, flat or ‘weeping’ and there are innumerable variations. A good variety of these tree shapes should be planted to provide interest and good contrasts. There is often plenty of rounded shapes, but not enough of the others, especially upright or conical kinds. Many garden trees are grown as standards, with a clear stem of up to 2 metres, which allows planting beneath.

 

Colour

 

Trees and shrubs offer a wonderful panoply of colour, provided by leaves, flowers, berries, bark and even buds. Flower colour is usually taken into account, but foliage colour, though at least as important, is often ignored and the other sources of tree colour are hardly even recognised. Aim to provide variety of foliage colour through spring, summer, autumn and winter by choosing trees and shrubs that change colour with the seasons. Those that vary from the standard green – yellow, bronze, red, purple, blue and grey foliage plants – deserve special consideration.

 

Texture

 

Texture is a feature of trees and shrubs that is less obvious than other aspects, and its value is not widely appreciated. The distinctive size, shape and density of foliage, and the way the plant holds its branch framework, define texture. For example, Japanese maple is soft and ferny; horse chestnut is bold and strong; Scots pine is rugged and untamed. Choose plants for variety of texture, which is every bit as important as shape or colour.

 

Cordyline australis ‘Albertii’

 

A large garden, greater than 1,000 square metres, can accommodate a small number of large trees and some smaller ones. Not nearly enough large gardens have good-sized trees, even one or two, although there is often plenty of space. A very wide choice of trees and shrubs is available to suit any garden site.

 

Trees and shrubs need good, fertile, moist – but well-drained – soil. Some types tolerate wet, heavy soil and others enjoy warm, dry soil. Thus a choice can be made for any soil type.

It is not practical to improve the soil for trees and large shrubs, because their root area is just too large, but proper planting will greatly help establishment. The soil area for smaller plants can be improved by digging in well-rotted manure, compost or peat and some general fertiliser, before planting.

 

Laburnum anagyroides

 

The acidity of soil can affect trees and shrubs. Very acid, peaty soil causes poor growth because the soil is low in available plant nutrients while limy soil causes some of the best garden shrubs – rhododendrons, camellias and heathers – to fail during to iron deficiency, iron becoming unavailable to these plants when grown in limy soil.

Slightly acid conditions, pH 6.5, are ideal for a wide range of plants. Hydrangeas are good indicator plants, carrying pink or red flowers on limy soils, blue on acid and a weak purple on neutral soils. Soil test kits are available and adequately accurate for most ordinary garden use.

 

Trees and shrubs are relatively tall plants and, therefore, prone to wind damage – Ireland has a very windy climate! Western and southern coastal areas suffer particularly from strong gales. Eastern and northern areas often get cold, dry winds in spring. The midlands, being flat, can be very windy too.

In exposed gardens, shelter is the first essential. Even where exposure is not great, trees and shrubs grow better with some shelter. Certain species of trees and shrubs tolerate strong winds and even salty gales. These species can be used to protect their more finicky cousins. Young plants especially need protection, but it must be remembered that too much shelter makes a garden cold and dark.

 

The effects of salt-laden gales

 

A useful shelter effect is achieved for a distance of 10 times the height of the shelter. In a very exposed situation, consider using artificial shelter to allow natural shelter to become established. Porous wooden fencing, or plastic netting, can be used to reduce wind – not to block it.

Solid windbreaks can increase the problem by forcing wind upwards, only to have it come down behind the barrier with even greater force. Note that these effects are often created around and between houses and, although the locality might not be exposed, parts of the garden can be very windy.

 

Trees carry their branches on a single stem, or trunk. Shrubs have a number of stems at ground level. Trees are generally larger than shrubs, but there are exceptions; dwarf trees – still truly trees – might be only a few feet tall.

 

Evergreen or deciduous

 

 

Trees and shrubs are either evergreen – retaining their leaves all year round – or deciduous – dropping their leaves each autumn. Trees that bear cones instead of flowers are called conifers. Evergreens can be broad-leaved evergreens such as holly and laurel; conifers with needles such as spruce and pine; or conifers with soft foliage such as lawson’s cypress and thuya.

 

Uses of trees and shrubs

 

 

Trees and shrubs are used in gardens for decorative purposes. Trees fill some of the space of the garden, counterbalancing the flat areas. They give privacy and provide a backdrop for smaller plants. Shrubs are more ornamental and provide variety of interest. Trees and shrubs are best planted in combination, to create a pleasing decorative effect.

 

 

Specimens

 

 

Exceptionally beautiful trees or shrubs can be planted as single specimens in a lawn area where their special qualities are put on show. Use only one specimen in a small lawn, or a small number of isolated specimens in a large lawn; otherwise the effect is lost.

 

Other uses

 

 

Climbers are used to decorate walls and fences. These woody plants make good use of vertical space that is often wasted. Some trees and shrubs make good hedges and screens. They provide privacy and respite from noise and dust. Evergreens are best against noise. Deciduous trees are best against dust, removing it each year when the leaves fall. Low-growing shrubs can be used as ground-cover plants to clothe the soil surface and help to keep weeds under control.

 

When the temperature level drops below -5 Celsius, some shrubs can be affected such as fuchsia. Below -10 Celsius, many others are damaged, such as cordyline, griselinia and phormium.

Temperature levels dropped to minus 12°Celsius in some places in the first two weeks of 2010 and perhaps a degree or two lower in others, some – 17. This is very cold – these temperatures are plumbed only every fifteen or twenty years, and then only for an exceptional night or two.

But the big freeze saw low temperatures last for a week and more, without thaw, depending on location. When this happens real damage is done to plant tissues. They freeze and the ice crystals slowly grow, just as the ice thickens on a lake, and eventually the ice bursts the cells and the cells die.

Very often this damage appears as dried out leaves, or mushy leaves, but sometimes the damage is done inside the plant, in the buds or in the cambial layer, that slippery layer of cells between bark and wood.

Cordylines and phormiums keel over, the soft centres of these plants killed by freezing. Griselinia and escallonia hedging too. The damage does not become evident for a few weeks, when anticipated growth does not happen. In the meantime, nothing to do but wait and see what happens. It is not unusual for some shrubs to sprout low down on the main stems or even from below soil in some cases.

Do not cut away the top until you can see where the new growth is coming from.

If you lift some bark with a knife at ground level and the wood is brown underneath in a few places, the shrub or tree is dead.