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.
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.
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.
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.
Once the only available material, glass is still the best, letting in light and retaining heat better than any alternative. It is more expensive and not as safe as plastics, but it lasts much longer. Safety glass is available, however, and though it is more expensive again than ordinary glass, it might be considered for a conservatory.
Not as dear as glass, and safer, but they do not let in as much light; nor do they look as well, except for perspex, but this is expensive, too.
This is usually polythene which is cheap and safe and lets in light but does not last so well. PVC and Ultra-violet inhibited films are more expensive than polythene but last longer.
A very wide range of irrigation equipment is available for garden use. Being made of modern plastic materials, it is relatively inexpensive. Much of this can be installed by the home owner, but larger gardens might need the services of a professional installer.
A hose, and perhaps a sprinkler, are essential in a large garden with a lot of watering to be done, or a garden on dry soil. A garden with a lot of pots will need a hose to speed up the frequent watering required. Very handy attachments such as storage reels for hoses are available. Sprinklers can be attached to tap timers to control the amount of water delivered.
A soak-hose, or leaky hose, has pores that allow water to seep out, gently watering the soil along its length. This can be left in position for long periods if necessary, for instance to establish a hedge in dry ground.
Fixed irrigation systems with drippers or small sprinklers are available for large and small gardens, and fixed lines with drippers are very convenient for watering containers, especially baskets and window boxes that might be inaccessible.
A set irrigation system is very convenient if watering must be repeatedly carried out, for instance, in the dry shade of trees.
Their main use, nowadays, is as colourful fillers-in, ideal for odd corners and gaps between other plants. They give a ‘cottage-garden’ look to a bed or border – a jumble of types of different heights and colours flowering over a period in mid-summer.
Hardy annuals are raised from seed sown in seed trays or directly in the ground where the plants are to flower. They can be sown in March, April or May. March sowings can be affected by cold, wet weather. May sowings can be affected by dry conditions and, anyway, they tend to flower late. Early April is usually a good time.
Seeds of some types can be sown in September, too. These over-winter as young plants and flower earlier the following summer than the spring sowings.
Dig the ground, working in general fertiliser at 70 grams per square metre. Break up all lumps and rake the surface fine. Some peat or organic material might be worked in too if the soil is poor. Make little drills with a stick about 15 centimetres apart and 1 centimetre deep. Sow the seed thinly and cover with soil.
If the area being sown is larger than about 1 square metre divide the space into areas of about this size and sow a few different types. Seed can be sown broadly scattered about too, but sowing in lines makes it easier to distinguish flower seedlings from weeds.
Hardy annuals grow best in good, fertile, but not over-rich soil in full sunshine. Some kinds, such as California poppy and pot marigold, can tolerate poor, dry soil.
Aftercare for hardy annuals
When the rows of seedlings can be distinguished, lightly run a hoe between them to kill weed seedlings. Weeds should never be allowed to get established. Watch for slugs and snails, too. When the seedlings are about 2 centimetres high, a first thinning can be carried out, though, if the seeds were sown thinly enough, this will not be necessary.
When the seedlings are 5 centimetres high, they can be thinned to their final spacing. This varies from 5 to 10 centimetres apart for small kinds to 30 centimetres apart for large types. If there are gaps, they can be filled by lifting and transplanting excess seedlings carefully.
Some of the taller types may flop about when grown on good soil. Bushy twigs might be used for support. Hardy annuals often self-seed, so areas of the garden might be set aside for this to occur.
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
House plants are attacked by quite a few kinds of pests because these appreciate the warm conditions, soft growth and the absence of predators.
Greenflies are the most common houseplant pest, greenflies, can appear on any plant at any time of year. Black, sooty moulds may grow in the greenflies excretions.
Red spider mites cause yellowing and curling of leaves and are difficult to control. Busy lizzie is often attacked.
Red spider mite damage
When a plant infested with white fly is touched, tiny white flies fly out. Though not as common as the other two, whitefly can cause severe stunting too.
Scale insects are protected by waxy scales and these sap-suckers can reduce growth and cause leaf-fall, especially on evergreen plants such as citrus. Scale insects can be controlled by dabbing with cotton wool dipped in methylated spirits.
Caterpillars and earwigs sometimes eat holes in houseplant leaves. Affected plants are usually near an open window. Damage is usually slight and not worth controlling.
Vine weevil grubs eat the roots of many house plants, especially cyclamen and woody plants. The adult weevil crawls into the house and lays eggs in the compost. Sudden wilting, although plants have been watered, and the presence of white grubs in the compost are the usual indicators.
Tiny black mushroom flies crawling on the surface of the compost, lay eggs that can feed on the roots as tiny larvae. These are an indication of over-watered compost and can be controlled by allowing the compost to dry out for a time.
Among the specific houseplant insecticides are: Derris, Malathion, Tumblebug, Kerispray, Bio Sprayday and Picket. Take the plants outdoors for spraying and spray all affected plants at the same time to avoid re-infestation.
Repeat if necessary. Alternatively, plants can be immersed, pot and all, in a bucket of diluted spray material. Use rubber gloves.
Root-rot is the most common disease of house plants, usually caused by over-watering. Affected plants often die.
Leaf and stem-rots are caused by various fungi, but mainly grey mould or Botrytis. Avoid over-watering or misting in the dormant season. Place plants in a warmer, brighter place. If they do not recover, discard them.
Soak-water the plant before potting. If the new pot is made of clay, put it in to soak too. If an old pot is used, wash off all traces of old potting compost. Place a piece of broken pot, or a flat stone, over the drainage hole if it is large.
Put some moist compost into the pot. Gently knock the plant out of the old pot, supporting the root ball on one hand, the pot with the other and tapping the pot edge against the edge of a bench or similar surface.
Try out the root-ball for depth in the new pot. Set it deep enough to allow 2-4 centimetres of rim space for watering, and one centimetre or so to cover existing root-ball with new compost. The bigger the pot the greater should be the watering rim space.
Fill in around the root-ball with new compost and firm gently. Clean the sides of the pot and water the compost lightly. Keep the plant out of direct sunlight for a few days after potting.
March/ April is the best time for potting because the plant gets the full benefit of the growing season. However, potting can continue through the summer until August.
Avoid potting in autumn and winter. There is generally no advantage in potting this late in the year – plants will not grow during that period and there is a risk of root rot diseases developing during the winter months.
Plants need to be re-potted when they outgrow their pots, which depends on the vigour of the plant. Every two or three years is enough for most house plants. The best indication that a plant needs re-potting is the compost drying out very quickly after watering, or the pot toppling over at a touch. Move gradually up through the pot sizes – do not put small plants into large pots.
Types of pots
Indoor plants are grown in a pot or container of some sort. The compost in the pot provides a medium for supplying moisture and nutrients, and it also supplies anchorage for the plant. As plants grow, they need to be moved into larger pots.
Ordinary soil is not suitable for house plants because frequent watering eventually cakes it into a hard mass, that admits neither water not air. An open compost is necessary for house plants, and compost for houseplants should be peat-based or contain a fair proportion of peat.
Peat-based composts include Shamrock Seed and Potting Compost, Erin Potting Compost, Bio Potting Compost and Levington Compost, Use lime-free compost Brown Gold, for lime-haters. Mixing these composts with garden soil, unsterilised, helps to deter vine weevils.
Plants need carbon dioxide from the air for growth. The old notion that it is dangerous or unhealthy to have plants in the bedroom at night is not true. Plants marginally increase the carbon dioxide level at night, having reduced it during the day – another person sleeping in the same room increases the carbon dioxide level many times more.
Roots need oxygen to live and for the uptake of nutrients. Air is excluded by excessive water in wet compost, causing the roots to die and eventually to rot. The roots ‘drown’ for lack of air, but this will not happen if the compost is open enough to allow air to reach the roots. Open, well-aerated compost is essential for healthy growth.
Air-borne dust is another pollutant that affects plants. House air invariably carries a lot of dust from open fires, clothing and furnishings. A thick layer of dust not only spoils the look of the plant but it reduces the amount of light reaching the leaves, which reduces growth.
Leaves should be cleaned from time to time, especially at the start of the growing season, by spraying with clean water or sponging large leaves. Leaf shine products, such as Bio Leaf Shine and Kerishine, can be used to enhance the shine of leaves, but only on naturally shiny-leaved plants. Do not use household polish, cleaners, oil or milk on house plants.
When to feed
House plants depend entirely on whatever nutrients are in the compost, or are added to it subsequently. Potting composts have enough food for about two months. After that, plants must be fed for continued good growth.
Dieffenbachia needs regular feeding
Which feeds to use
Soluble plant food formulations are easy to use and safe for the plants. Solid fertilisers too easily lead to overfeeding and it is best to stick to special houseplant feeds. There are many brands: Phostrogen, Kerigrow, Baby Bio, Hygeia Plant Food, Miracle Gro, Algoflash, Shamrock and J. Arthur Bowers.
Some brands are high in nitrogen, which is the first figure in the analysis given on the packet or bottle, for instance 10:2:4. These are suitable for foliage plants. Flowering plants need a more balanced feed, such as the formulae 7:7:7 or 5:4:4.
Most kinds of plant food contain trace elements. Use slow release plant food tablets, or spikes, to reduce the frequency of feeding.
Too much feed
In extreme cases, too much plant food can cause a plant to wilt and die, especially when excessive plant food is applied to a dry pot. Constant over-feeding can cause stunting and brown edges to the leaves.
Quite often, over-feeding causes rapid, dark-green leafy growth at the expense of flowering; this is typical of geraniums. Over-feeding can give rise to a white salt deposit on the compost surface. However, in a ‘hard’ water area, this simply may be lime in the water that rises to the surface of the compost.
Too little feed
When plants are short of nutrients, growth is weak with small, pale leaves and thin stems. Often the leaves have yellowish blotches, or markings, between the veins.
On poorly fed plants, the flowers sometimes have poor colour, and the flower heads tend to be small. Stems and leaves can take on a purple tinge, especially in peat composts. Older leaves, or young leaves, can go yellow, and fall off or shrivel. Stems are spindly.
The method of watering has an influence on the frequency. Soaking the pots to half their depth in a basin of water will ensure that a full complement of water is absorbed. Allow to drain afterwards. Plants watered by this method
Watering from the top of the pot is easier because the plants can be watered in situ. Fill the rim space with water. If it soaks away quickly, fill it again. It can be quite difficult to re-wet dried out posts by this method as much of the water escapes between the compost and the pot.
A good compromise is to soak-water every third or fourth watering during the growing season. In winter, top-watering is best, because a full soak-watering might leave the compost too wet, with little prospect of drying quickly enough.
Always use water at room temperature, as cold water can cause plants to drop their leaves. Use only ‘soft’ water for azaleas, citrus, camellias, stephanotis, and indoor heathers. If the water supply is hard – ‘fur’ in the kettle – use rainwater, or melted water from defrosting the fridge.
Wet compost is cold, and this can slow down or even stop growth. On over-watered plants, new leaves can be small and weak. In winter, cold, wet compost exhausts the plant’s food reserves, the leaves turn yellow and fall off, or parts of leaves turn brown, often without drying out.
Do not stand plants in a saucer or tray of water, especially in winter. It is very common for entire plants to die if rotting of the roots follows over-watering. A heavy pot is a good indicator of too much water.
Too little water
Wilting is the most dramatic manifestation of water shortage. The plant cells, empty of moisture, deflate like a balloon and rigidity goes from the leaves and soft stems. Following wilting, plants seem to recover upon watering, but later, brown patches often develop.
Plants that frequently run short of water, even without wilting, suffer considerably, because parts of the root system may die. Growth is often affected – new leaves will be small.
Flowering can be hastened but the flowers tend to be small and often shrivel without opening. Dry plants look ‘hard’ – often with a bluish or greyish tinge. A light pot is a good indicator of dry compost, even though the surface looks moist.
Water is a critical need of house plants for good growth, and for keeping them cool by transpiration – the plant version of sweating. It follows that more water is needed in the warm months. Water is lost from the compost in the pot and through the pot itself if it is made of clay.
Gloxinia rots when over-watered
The ‘Touch Rule’ is a simple test. Place a finger firmly on the compost in the pot. If it feels dry and hard, the plant may be in need of water. If it feels cool and soft, the plant has enough moisture. If it feels cool and wet and moisture remains on the skin, the plant is over-watered.
In the October to March period, house plants need only a fraction of their summer requirements. Using the ‘Touch Rule’, keep the plants between moist and dry – certainly not wet. Ideally, the compost should be dry on the surface and moist just below. Plants maintained slightly on the dry side resist cold and disease much better.
Watering will be necessary only every seven to thirty days in winter. The winter flowering house plants make an exception to the general guideline. Cyclamen, azalea, poinsettia, potmums and christmas cactus should be kept just moist in winter.
Coleus likes warm conditions
Although house plants need warmth for growth, the main concern is to provide conditions warm enough for healthy survival through winter. Many house plants come through winter in such bedraggled condition that they are thrown out. Because indoor temperatures are usually higher than outdoors, most of the plants used as house plants are native to warm climates.
Partly heated rooms
Busy lizzie is quite tolerant
Rooms that are heated for part of the day in winter are suitable for the majority of house plants. The temperature usually stays above 10° to 12° Celsius, and this is adequate for most house plants. Flowering house plants stay in flower longer in cool conditions.
Rooms that are not heated at all are suitable for only a limited range of house plants. On a cold night, temperature levels can fall to 5° Celsius in such rooms, and even close to freezing on occasion. These are harsh conditions for house plants and many types will lose condition.
Plants that can survive unheated rooms include geraniums, rubber plant, fatsia, ivy, silk oak, spider plant, mother of thousands, cacti and succulents, cyclamen, primula and cape primrose. Note, that behind the curtains of unheated rooms, plants might be exposed to frost.
Freezing conditions often occur in greenhouses and conservatories in winter, and since very few house plants can survive sub-zero temperatures, greenhouses are not suitable for overwintering house plants unless artificially heated.
Too much heat
Excessive heat is usually localised – caused by heaters or radiators. Any plant in direct contact with a heat source will be scorched and, even though the heater can be some distance away, brown marks could still appear on the leaves nearest to the source. If the air in the room is generally too warm and dry, brown edges often develop on the leaves over a period of time.
Too little heat
The main symptom of a problem with low temperatures is leaf drop. Plants drop leaves for several reasons – too much water, too little water, root damage, old age – but in winter, if leaves drop off suddenly, it is usually from cold. They are often still green when they fall. Some plants sacrifice part of the leaf, which later goes brown.
Many plants can adapt to low temperatures over a period, but even normally hardy plants can suffer if they get a sharp shock. This can be caused by a sudden move from a warm room to a cold one, or by draughts causing low temperatures at floor level.
Avoid sudden changes and, if plants are suffering move them for a while to a warm room to recover. A first sign of trouble, very often, is listless appearance – a slight droopy look – not quite wilting. Plants can tolerate cool conditions better if they are getting good light and are not over-watered.
Most indoor situations have some light. This ranges from very little to quite a lot – even within a average-sized room. There are plants to suit any situation where daylight reaches.
Croton needs good light
In really poor light situations, leave the plants in position for only a couple of months at a time, rotating them between good light and dull conditions. Otherwise consider installing artificial lighting of sufficient power to allow plants to grow in shaded corners. The lights should be aimed at the plants, and placed fairly close to them. Use ‘cool’ lights that will not scorch the leaves.
Green foliage plants tend to turn pale yellow-green, and variegated foliate plants tend to lose their variegation if there is too little light. Flowering plants flower badly, or not at all. Plants become lanky, with smaller leaves on long leaf stalks and with bigger gaps in between, and they turn towards the source of whatever light there is.
The majority of house plants need good light, such as the window-sill of an east, or west-facing room and near, but not on, the window-sill of a south-facing room. Flowering house plants, variegated foliage plants and green foliage plants all need good light – the needs of flowering plants being greatest and those of green foliage plants least.
Many house plants – mostly the foliage kinds – cannot tolerate the very bright light in south-facing windows and porches. Some plants revel in it, such as geraniums, cacti, succulents, yucca and bougainvillea.
Fading is the tell-tale sign of too much light. Flowers lose their colour and often dry out at the edges of the petals. Foliage plants often fade to yellowish green, and variegated plants, though they enjoy some sun, may fade to whitish yellow. Ferns go brown from scorching, and other plants can develop brown spots on the leaves too. Danger time is summer.
Flowering house plants can be very short-lived – in some cases they just one step up from cut flowers – or they can be quite long-lived. Some types, such as cineraria and primula are disposed of after flowering finishes.
Hippeastrum makes a good house plant
Others, such as begonia and cyclamen, have a bulb or tuber that is retained to flower again; and some such as geranium and azalea that stay green and leafy after flowering, are grown on as foliage plants until they flower again.
Other greenhouse vegetables
Early and late season supplies of carrots can be had from the greenhouse, frame or low tunnel. Sow ‘Early Nantes’ or ‘Amsterdam Forcing’ in December or January for supplies in late May and June. A late sowing of the same varieties in August gives a December crop.
Early carrots from a cold frame
White turnips, broccoli, radish, scallions and parsley can be grown under protection too. Sowing can start in January in a cold greenhouse or frame, December in a cool greenhouse. Delay sowing until early February under low tunnels but put up the tunnels about three weeks before sowing.
Florence fennel and chinese cabbage are two crops that are difficult to get right outdoors – they both have a tendency to bolt if the weather is not warm and moist. Sow florence fennel in late March and chinese cabbage in May. Keep both well-watered to prevent bolting.
Early and late potatoes can be produced under protection. Planted in December or January they will be ready in May.
In August, plant strong runners 30 centimetres apart outdoors in good soil. In October, lift the plants and carefully pot then in medium-sized pots. Leave the pots outdoors until the middle of January and then bring them into the greenhouse, or frame.
Early strawberries in flower
When the plants begin to grow, check them for greenflies and spray, if necessary. Depending on the level of heat available they will flower in March/ April and fruit in April/ May.
Alternatively, the plants can be covered, where they were planted, by a low tunnel to fruit in May/ June. Plants ‘forced’ under glass or plastic can be planted out and grown on outdoors, but are not worth forcing again.
Peaches, nectarines and apricots are closely related stone fruits that can be grown in a greenhouse as fan-trained trees on a wall. The trees can take up quite a lot of space, especially the apricot, but they can be hard-pruned too. ‘Peregrine’ is a common variety of peach and ‘Early Rivers’ is a nectarine variety.
Peaches can be raised from pips of shop-bought fruit and, unusually among garden fruits which are mostly grafted, will come true to type. Plant a young tree into the open soil and train it to a fan shape by tying in the branches to wires, set 30 centimetres apart, that run the length of the wall to be covered.
Pollinate the peach flowers by hand, using a child’s paintbrush, or by tapping the wires each day during flowering. If a lot of fruits set, thin them out to about 15 centimetres apart. When the fruit is picked in August, immediately prune out the shoots that have carried fruit and tie in the new green ones to flower the following year ones.
In the spring, when the buds break, rub away excess young growth, leaving only enough shoots to replace the fruiting shots and maintain the branch framework. These trees always produce too many shoots.
Never let the roots go completely dry. Use a mulch and water as necessary. Watch out for red spider mite and use the predatory mite for biological control, or spray with Sybol, Malathion or Liquid Derris, if necessary.
A grapevine can be grown successfully in quite a small greenhouse, but the bigger the better because a grapevine can fill quite a large greenhouse. ‘Black Hamburgh’ is the best variety for Irish conditions. Planting is usually done when the vine is dormant in December but the plants are pot-grown and can be planted at any time.
Grapes swelling on the vine
Grapevines are often planted with the root outside the greenhouse and the stem taken in through a hole in the wall or wall-base. It is not essential to plant outside, although it reduces the vine’s watering needs, but the roots will generally grow out under the wall in any case.
Train the vine to grow up into the roof of the greenhouse. First, train it up to gutter height. Then train a single shoot along the wall at this height. When it reaches the other end, allow side-shoots to grow up the roof on wires, tied into place 30 centimetres apart.
From these side-shoots, which form permanent rods, come the flowering shoots. These arise every 30 centimetres or so. Allow only one shoot to develop at each station and pinch out its tip one or two leaves past the flower bunch. Tap the rods each day, during flowering, to ensure pollination. Pinch out subsequent side-shoots at one leaf.
Grapevines are normally vigorous but if not, mulching the root area in spring will encourage better growth. Use some general fertiliser as well, if growth is weak or after a heavy crop. Watch for red spider mite.
Powdery mildew is a serious problem disease. It is important to allow air movement in the greenhouse. Rose and fruit fungicides containing the active ingredient myclobutanil are highly effective, and one or two thorough applications in late spring on the new foliage before flowering will clear the problem.
Grey mould disease can be prevented by ventilation and maintaining a dry atmosphere in late summer. Prune out the fruit-carrying shoots in autumn when the fruit is picked, leaving the framework of permanent rods.
Shrubs and climbers
A wide range of ornamental plants can be grown in a greenhouse or conservatory. Some of these must have the protection of a greenhouse and cannot be grown successfully in the open garden. Other plants, though they can be grown outdoors, grow better with the extra heat provided inside a protective structure.
Freesias need greenhouse protection
A wide range of herbaceous plants, such as busy lizzie, streptocarpus, pelargonium, cymbidium orchid, canna and peruvian lily, can be grown in the greenhouse. Some of the indoor plants are bulbs, corms or tubers such as gloxinia, tuberous begonia, amaryllis and lily that are potted up in March or April.
Freesia, cyclamen and anemone can be potted up in August or September. Hyacinth, tulip grape hyacinth, crocus and dwarf iris can be potted up in September or October and brought inside in January. Most of these plants come into flower four or five months after potting up.
Many greenhouse flowers can be raised from seed. Cineraria, primula, calceolaria and butterfly flower are sown in June, July or August to flower in March, April or May of the following year. Cyclamen is sown in August to flower 15 months later.
Quite a few bedding plants, both spring and summer, can be used as flowering pot plants. Petunia, everflowering begonia, ageratum, tobacco flower and french marigolds can be sown in March to flower in summer.
Polyanthus and double daisy are sown in early summer, and stock in late summer, to flower in spring. Two very useful greenhouse plants also raised from seed in spring are morning glory and blackeyed susan. These are climbers, but they only last one season.
Many foliage plants, such as spider plant, tradescantia, coleus and ferns can also be grown in a greenhouse. Shading might be necessary to avoid sun scorching and, in winter, some must have frost protection, or be taken indoors.
Greenhouse alpine: Primula allionii
Because they need very little space, alpines make excellent greenhouse plants. They enjoy the dry air, but they mostly dislike excessive heat, and are best placed near the door or the ventilator. In winter, it is important to keep air humidity as low as possible.
Special alpine houses with a lot of ventilation are sometimes set up by alpine enthusiasts. Many kinds of alpines, such as primula, raoulia, lewisia, gentiana, rhodohypoxis and many small alpine bulbs, can be grown indoors.
Plants in a greenhouse need extra care because of the high temperatures generated and the exclusion of natural rainfall.
Christmas cherry with other greenhouse plants
Ventilation on hot days is necessary to keep plants cool. About 25° Celsius is an ideal maximum for most plants. Beyond that, growth slows down and stops. High temperature levels can be reached from late spring onwards.
In summer, ventilation alone might not be enough, so shading can be necessary. Apply Coolglass, or Summer Cloud, in June or early July and remove it at the end of August. A simple way of cooling the house on really hot days is to damp down the floor. Ventilation in winter and spring, on dry, bree days, dries the greenhouse atmosphere, helping disease control.
Greenhouse plants must be fed much more often than plants outdoors. The frequent watering that greenhouse plants receive tends to wash the soluble plant nutrients from the restricted reserve of a pot.
Feed little and often – even as often as once a week for large, quick-growing plants early in the growing season. Liquid feeding is simplest to use and most effective. Take care not to feed a dry pot, for fear of scorching the roots.
Pest and disease damage is usually more severe in a greenhouse, where the warm conditions are ideal for insects and fungi, and predators are absent. Remove old and diseased plants, or pest-ridden plants, to break the cycle of infection. Control pests and diseases when they appear.
Wash down the glass, pots, trays and benches in the winter with household disinfectant. There are no products approved for domestic use in disinfection of greenhouse soil. If the soil is ‘tired’, replace it with fresh soil. If there are root disease problems, grow non-susceptible crops. Flood the greenhouse soil in early spring by watering heavily to leach out excessive salts left over from frequent feeding the previous year.
To trap as much heat as possible, a greenhouse should be situated in an open, south-facing position without shading from buildings or trees. The ridge of the roof should point east-west, the broadest part of the glass exposed to the sun. This does have the drawback of heating more on one side, and this can be avoided by running the ridge north south. For warmth, the next best side-on aspect is west because it heats up late in the day, and stays warm longer into the night.
Strong gales can cause severe damage
An east-facing side-on site goes cool even before sunset and the morning sun can cause damage to plants by too-quick thawing. A north-facing greenhouse, to be of any use, will need artificial heating – even for the usual range of plants.
Do not site a greenhouse in a hollow where cold air might seep in, nor in a windy position. Do not forget the strong eddies of wind around a house, though the site might seem sheltered.
A ‘cold’ greenhouse means that there is no artificial heat provided. A ‘cool’ greenhouse has a heating system that will provide some artificial heat – usually just enough to protect against frost. A ‘warm’ greenhouse has a heating system capable of providing an air temperature of at least 10°Celsius.
Greenhouse flowers can be very rewarding
If basic frost protection is all that is required, there are two options – paraffin or electricity. A simple paraffin heater is relatively cheap to buy, and to run, but needs to be lit and refuelled, and can give off damaging fumes if not set up correctly.
An electric fan heater is more expensive to buy, but very easy to operate, usually featuring a built-in thermostat. Seek professional advice when installing an electric heater and be sure to set it up so that it does not get wet.
Running costs for a fan-heater are low, if it is used only for frost protection. A two kilowatt fan-heater will keep a 3.6 metres by 2.4 metres greenhouse free of frost on a night when it is minus 8° Celsius outside.
Heating a warm greenhouse to about 10° Celsius is a more difficult proposition. An extra radiator can be taken off the domestic heating system if a conservatory or greenhouse is attached to, or very close, to the house. Most central heating systems are on a time switch that shuts down the system at night – just when the greenhouse needs it most!
However, usually enough heat will have built up earlier to protect plants adequately. A thermostat over-riding the time switch can be installed to prevent very low temperatures.
Electric storage heaters can be used in a conservatory too. These use night-rate electricity. There must be no danger of them getting wet, for safety reasons. They tend to be bulky too. Free-standing greenhouses are difficult to heat economically beyond basic frost protection. A separate hot-water boiler is ideal, but few people would consider this necessary or affordable.
On a sunny day in summer, greenhouse temperatures could rise above 40° Celsius. Plants dry out quickly and can be scorched or killed at these temperatures. It will be necessary to allow the hot, dry air to escape.
Vents in the roof and sides should be provided. Opening the door helps too. Roof vents are important not only because hot air rises, but also, because it may not be possible to leave side vents or doors open in a conservatory for security reasons.
Polythene tunnels are difficult to ventilate properly, usually relying on leaving the ends open. This is adequate, once the tunnel is not too long.
Glass was once the only available glazing material, and it is still the best, letting in light and retaining heat better than any alternative. It is more expensive and not as safe as plastics, but it lasts much longer. Safety glass is available and, though it is more expensive than ordinary glass, it should be considered for a conservatory.
Low polythene tunnel with early potatoes
Rigid plastics are not as expensive as glass, and they are safer, but they do not let in as much light; nor do they look as well, except for perspex, but this is expensive, too.
A new greenhouse, well stocked
Polythene is cheap and safe, and allows in light well but does not last so well as the other materials. PVC and U-V inhibited films are more expensive than polythene but last longer.
A garden frame is just a large, low bottomless box with a translucent lid. The sides of the box can be made of wood, concrete, galvanised iron or any other building material – very often salvaged scrap materials will do.
The frame can be any length but should not be wider than 120 centimetres for comfort and safety. It should be 25 centimetres high in front, and about 50 centimetres high at the back. The ‘lid’ is a number of ‘lights’, each consisting of a wooden frame with glass or plastic – on it. Each ‘light’ matches the width of the garden frame in its own length and should be about 75 centimetres wide, and can be made of suitable timber lengths.
A ‘cloche’ originally was a bell-shaped glass jar placed individually over tender plants. The term was extended to include continuous structures of glass sheets supported by iron brackets. These continuous cloches were normally about 45 centimetres high but are now unusual, because low plastic tunnels and cloches have taken over.
A ‘walk-in’ tunnel, or polytunnel, can substitute for a glasshouse. Being relatively cheap to put up, it is possible to cover a larger area economically. A polytunnel can be of any length – using a greater number of the tubular steel supporting hoops.
Tunnels are generally sold as kits and the standard widths commercially available are 4.2 metres and 5.1 metres. Walk-in tunnels can be difficult to ventilate properly, and the plastic will have to be replaced. It usually lasts two or three years, although there are more durable kinds of plastic film that last for five years.
A low tunnel is a row of wire hoops – 45 centimetres high, 75 centimetres wide – supporting a 1.8 metre wide polythene film. Length of row is variable. At each end of the low tunnel the film is tied firmly to a short stake. The wire hoops are 1.8 metre lengths of strong wire with an ‘eye’ twisted into them about 20 centimetres from each end.
Strings tied into each ‘eye’ and stretched across the polythene hold the tunnel film in place. Although both garden frames and low tunnels are limited in use by their size, they are very successful for low crops such as early and late vegetables, early strawberries, and cuttings.
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