Garden Walls

New Zealand Journal of Agriculture, Volume 99, Issue 2, 15 August 1959, Page 183

Garden Walls

4

K. H. Marcussen,

cu t,

HILL gardens have a natural charm, but work in them can be difficult. Terracing will make gardening easier and when walls are judiciously fitted into the landscape they can become a feature. Types of walls and their construction, merits, and faults are discussed in this article.

TERRACING by several small walls is usually the most desirable method in hill gardens because construction is easier and also the character of a hill garden is retained. A high wall is generally unattractive. Even if in time it can be covered with trailing plants, it does not provide scope for growing the mixture of plants which makes hill gardens so attractive. Frosts are generally not the same problem in hill gardens as on flat sections, but frost danger is relatively less on a sloping section than it is on a terraced one. The wider a terrace the greater is the chance of it becoming a frost pocket and the nearer the bottom of the hill the greater this danger becomes. Underground springs are often encountered where a large excavation is made for a wall and require adequate outlets, but where it is possible to break the hillside up with several smaller walls drainage can more readily be provided. A series of smaller walls are much easier to make. Not only is the job simpler, but also it can be done over a period. Each wall can be made as time and finance permit and there is less interference with the general development of the garden. Walls should not be made too long. A garden will be more interesting if the terraces vary a little in levels and extent. Terracing of a hill section done with the strength and enthusiasm of youth will make work in the garden so much easier in later years. Foundations It is of utmost importance to have a firm foundation to a wall. This is seldom difficult on a slope, as the subsoil is mostly hard clay, rock, or papa, but not so where a hillside has been levelled before building was started and considerable quantities of loose soil have been thrown down the slope. With such unstable soil it is risky to build permanent walls, and, in general, it would be wiser for an amateur to build a temporary wall until the soil has settled.

Drainage Drainage must be efficient, as water can weaken the foundation and it is better to be over-generous when making drainage holes than to make too few. It is preferable to place them at different levels along the wall with adequate drainage at the foot of the wall. Drainage holes can easily be made in concrete or mortar walls by inserting round bottles during the construction. If they are given a slight turn occasionally while the concrete or mortar is hardening, they can be pulled out afterward.

It may. be necessary to provide a drain at the foot of the wall and the flow will determine the size that is needed. Concrete Walls Concrete walls are the easiest to make, but reinforcing, is necessary if there is much height or stress from the soil behind. Where a low wall can be placed on a firm foundation and where there is no risk of movement of the soil behind, an ordinary concrete wall will generally suffice.

Details on construction and materials for concrete and mortar are given in the Department of Agriculture Bulletin No. 345, “Concrete”, available free from the nearest office of the Department. Though concrete walls are durable and easy to construct, they cannot be fully recommended. An occasional concrete wall may look neat, but a series of them tends to give the garden a cold atmosphere. Their outline is hard and. they do not mellow and blend into the surroundings as do stone or brick walls. Stone Walls Stone walls can be made just as durable as concrete walls; in fact, a stone wall is often faced only and concrete poured in behind to strengthen it. They are, however, much more informal and pleasing than plain concrete walls. Sea or river boulders or rocks dug out of the ground can be used, but split quarry stone is much easier to work with. Such stones generally have one flat surface, which can be used for facing, and their irregularity facilitates placing. A stone wall should preferably be embedded in a concrete foundation and a batter, or backward slope, of at least 1J in. per foot of height should be given. Placing of the stones is simplified if a fairly “fat” mortar of lime, cement, and sand is used. No empty pockets should be left and the mortar should be worked well in between the stones. The face of the wall should be finished neatly, or the crevices between the stones can be pointed. The back does not have to be finished off as carefully, especially if concrete is to be poured behind. If this is not done, mortar should be used at the back to strengthen the wall and a long stone pointing into the terrace should be placed occasionally to tie the wall into position. The soil should be well filled in below these ties to ensure that they are kept stable while the mortar is drying. Split stone can also be used for steps and paths and if that is intended, the stones should be sorted while they are being used to save chipping them into shape. Buttresses in stone walls are not necessary, as the stone should have enough character to make it interesting, and if strengthening, is required, it can be given inconspicuously at the back of the wall. Concrete Block Walls Concrete blocks can also be used for garden walls and various types are now available. If the blocks are used to make a close wall, with the blocks mortared together, the result is more pleasing than a plain concrete wall, though still very formal.

Block walls must be made more carefully than stone walls, as the slightest irregularity will be noticed, but the blocks are easier to line up than uneven stone. Hollow blocks have the advantage that if they are placed correctly on top of each other, reinforcing rods can be inserted after the wall has been built and concrete poured in to finish the job. • Blocks can also be used for making a “dry wall”, described later, when their uniformity of size and shape enables their placing to be more secure than uneven stone. Brick Walls Though brick walls are formal, they fit into the garden much better than concrete walls. They should be well made and if strength is required, this can be provided by buttresses, which do not look out of place in this type of construction. Brick walls can be made in pattern in the same way as concrete blocks; any change from the normal will make the wall more interesting. If steps are made between the terraces, they will look more attractive if made in brick also. Timber Walls Wooden walls are more temporary than the others dealt with, but if soundly made will last for some years. Both sawn and rough logs may be used. Preserving treatment will prove well worth while before their use. The timber is generally placed horizontally in even lengths, being joined behind the posts. Placing of the posts is most important. They must be strong and set deep enough to hold the weight of the soil pressing against the wall. A batter of 3 in. per foot of height will ease the strain on the posts. Timber walls can often be made cheaply after completion of a concrete dwelling, as the boxing can be used. An advantage is that drainage will be better provided for than in a solid wall. Corrugated Iron Walls Second-hand corrugated iron can be used for walls in the same way as timber. More supporting posts, however, should be used, as iron sheets may bend in the centre under pressure and if that happens, it is a major job to get them back in position again. The iron should be treated before use with a rust killing preparation. Bituminous roof paints are excellent and provide a good seal on the side into the soil. Timber and iron walls are temporary only.

Dry Walls Dry walls are made of stones packed with soil and no cement or mortar is used to bind them. Concrete blocks are now also . used for this type of wall, but as the effect in the garden and method of use are quite different, they are dealt with separately. . Dry walls of stone are satisfactory only for low walls. In most places they are very expensive to erect, as a great many stones of good quality are required. The only justification for this type of wall is that it is possible to plant between the stones, but maintenance costs today are so high that they are seldom built. As with other permanent walls the foundations must be solid and drainage must not

be able to weaken it. A. tile drain may therefore be needed on the back of a wall to take away any seepage which may come down through the naturally sloping subsoil. Its unstable nature makes it much more prone to collapse under pressure than a solid wall. The stones should be fairly large and rough to ensure a good grip. Quarried and split stones are the best, but even then it may be necessary to shape them to make them fit firmly. River and beach stones are generally not suitable, as their smoothness prevents them from being placed securely. A batter of 3 in. per foot of height should be given and the largest stones should be used at the bottom of the wall. Each stone should be laid so that any movement is backward, where the soil will prevent it from slipping, but, generally, movement should be prevented by a firm packing of soil and smaller stones. Good garden soil should be used in the wall to sustain the plants grown in it. It is possible to plant while the wall is being constructed and the roots can then be spread out in the soil between the stones, but of course, it must be the right season. The stones on top should be as securely fitted as the others and large

enough that they cannot be dislodged by children. It is much simpler to construct a wall of concrete blocks, or evenly shaped stone because the blocks or evenly shaped stone can be placed firmly on each other, the joining surfaces can be reduced and a patterned interval allowed. This reduces the weight of a wall and gives greater flexibility. Block walls, or crib walls, can therefore be built higher than other types of wall without reinforcing. Proof of their strength is that such walls are used in road construction, where safety is of paramount importance. Construction of a very open crib wall is illustrated. Crib walls are sometimes attempted in brick, but the weight and size of the bricks are not enough to anchor them securely. Providing Plant Cover No matter how attractive a wall may be in itself, its appearance will be improved when the outline has been softened with plants. They can be used trailing from the top as well as growing at the base. Dry walls, of course, provide much greater scope, as plants can be rooted between the stones. . However, there is a danger that perennial weeds may be intro-

duced and they are almost impossible to eradicate without using chemical weedkillers. Fairly full cover can be recommended for plain concrete walls, and vigorous trailers such as aubrietia, morning glory (Ipomaea leari) , arctotis, and Dimorphotheca ecklonis are suitable. Stone and brick walls should be partly covered only and sprawling plants of compact habit are more suitable and can be used with the less vigorous trailers, such as alpine dianthus, Campanula sp., Sedum sp., Mesembryanthemum sp., Alyssum saxatile, gazania, and the trailing rosemary. Further information on the layout of hill gardens and suitable plants is provided in the February 1959 issue of “The Journal”.

Work for September

September is a busy but interesting month in the flower garden, as many different plants are beginning a new season’s growth cycle. This is

most marked in the colder areas, where the dormant season is more definite and spring blossoms are even more welcome. Because of the warmer and earlier spring in northern districts sowing and planting of summer flowering plants can begin earlier. What to do with Seeds With a little care several packets of seeds of annuals can give a most effective display over a long period in summer at little cost. If there is a

suitable warm and sheltered position in the garden, the top 6 in. of soil could be enriched with sieved compost and lightened with sand if necessary before the application of fertilisers and the sowing of seed. Such a position is, however, often the treasured place for spring flowering plants and for this reason and also the fact that seedlings are not so easily lost when in boxes, it is generally recommended that seed be sown in boxes which are 2 to 4 in. deep. The boxes should' be cleaned and sterilised by watering with 1 part of formalin in 49 parts of water. A layer of coarse rubble, leafmould, or coarse sievings from the compost heap can be placed in the bottom to assist drainage. When making a mixture in which to sow seed it is not so important to follow a recipe as to achieve a mixture which is quite open and yet has some body. Loam gives body and supplies small quantities of nutrients. Organic matter also gives body and helps retain the moisture and added nutrients. A

guide for the making of such a mixture is: 2 parts of sieved fibrous loam 2 parts of sieved leafmould, peat, or compost 1 part of coarse sharp sand plus 1|- oz of superphosphate and 4 oz of garden lime

per bushel of mixture (about an apple box). All ingredients should pass through -J in. sieve. When sowing in the open ground twice this quantity of superphosphate and lime should be used per square yard. Boxes should be filled level with the mixture, the soil should be consolidated with the fingers, especially at the sides and corners, and then smoothed and firmly levelled with a float (flat piece of board) . . The seed should be dusted with thiram, sown thinly, and pressed into the seedbed with the float before it is lightly covered with sieved mixture. The box should then be placed in 2 in. of water (a washtub is suitable) and left until moisture shows in one or two places on the surface. The box should then be removed, covered with glass and then newspaper, and placed in a warm place in no danger of drips from the roof. When seedlings begin to show the paper should be removed and two days later the glass can be removed. What Seeds to Sow Under glasshouse conditions the above method can be used for seeds which require warm conditions for germination. Outdoors, hardy plants which are to be transplanted, can be sown in boxes, while hardy plants and those which develop best when sown where they are to flower can be sown in the open. Of this latter group, linum, viscaria, mignonette, and love-in-the-mist are useful for sowing in pockets among permanent plantings to give an added splash of colour and interest. When the Seeds are up Seed sown previously may now be up and should be given frequent atten-

tion. It is usually better to water seedboxes by soaking in water than by sprinkling, which may create humid conditions conducive to trouble from the damping-off fungi. As soon as seedlings have their first pair of true leaves they can be pricked out 2| in. apart each way into a mixture with more body and more fertilisers. Plants being hardened off in frames should have the lights lifted when possible. It has been found that polythene is a doubtful replacement for glass on frames, as it allows quick escape in the night of heat built up during the day. This deprives plants of the protection they still need. Pansies and violas could be planted out now and make attractive borders round permanent beds of roses or fuchsias. Bulbs Need Attention Many spring bulbs are now past their best and the tops can be neatly tied in knots so that they continue to feed the bulb. DDT round the base of the plants will help prevent damage by narcissus bulb flies. New bulbs should be ordered while the varieties are still in flower. It is preferable to visit a good grower and see the varieties under field conditions rather than to order purely from the show bench. Tulips which have been attacked by virus should be dug up and burnt. Summer and autumn flowering bulbs and roots such as cannas, agapanthus, galtonia, and acidanthera can now be planted. Gladiolus nanus (vars. “Colvilii” and “The Bride”) should be planted by now and a few of the large gladiolus can be planted successively to give a continuing display from Christmas on. Plants in the Border Division and replanting of herbaceous perennials should be attended to urgently, as they are now starting into growth. Catmint, useful as a border and along driveways, can now be cut back and divided up if the clumps are too large or if required for extension. Gerberas can be broken apart now and planted in warm, sunny locations. The crown of the plants should sit above the soil when planted. Lily-of-the-valley and other plants nearing flowering will benefit from applications of weak liquid fertilisers. The whole flower border should now be given a dressing at 4 oz per square yard of balanced fertiliser made by mixing 3 parts of blood and bone 2 parts of superphosphate 1 part of sulphate of potash Cuttings of agathea, marguerite, hybrid wallflower, centaurea, and violet can be placed in sandy mixtures in a frame to root. Chrysanthemums and Dahlias If the planting positions of chrysanthemums and dahlias are alternated,

the build up of plant diseases which attack each crop is not so great. Both plants are gross feeders and repay all efforts to incorporate farmyard manure, compost, seaweed, and similar materials as well as regular balanced chemical feeding. Lime at 2 oz per square yard could also be given now. Three-inch cuttings from the tips, of chrysanthemum shoots should be neatly trimmed and placed in a box of a sandy mixture to root. In cooler districts they could be placed in a cold frame, but in the warmer areas they can be set outdoors. A sheet of paper should be placed over the box to stop the cuttings from flagging. Cuttings rooted in this manner will give shorter plants of bushier growth than those grown from rooted slips.

Dahlias can be encouraged, in frostfree positions, to send up new shoots. The tubers can later be divided or the shoots removed and set in a warm position to develop roots. Eelworms Eelworms cause sections of chrysanthemum leaves to turn dark brown and the leaves to shrivel and hang down. The damage usually starts at the base and extends upward until finally the whole stem is defoliated. Many spring flowering bulbs are also damaged, the attacks causing blisterlike swelling of the foliage and distortion and yellowing of the flower stem and foliage. In New Zealand eelworms are also known to attack delphiniums and scabious. Eelworms

are very specific in their host range and some types of eelworm . will attack only one type of plant. For home gardeners the only possible method of control is the treatment of plants with hot water. This has to be done very carefully. Overseas work has shown that the growing roots of French and African marigolds give off a substance which will reduce the numbers of some types of eelworms. It may be worth while to plant this easily grown crop in infected soils. Grassed Areas Sowing of new lawns and topdressing of bare, patches should be attended to as soon as possible. Grass grub has been so bad each year that the recommendation for their control is repeated this month, which is a suitable time to treat the ground before the grubs pupate. It is easiest to apply the DDT when mixed with the spring fertiliser application of 30 oz of sulphate of ammonia 10 oz of superphosphate 1 oz of 50 per cent DDT to 40 square yards of lawn DDT should be applied to the flower and vegetable gardens as well, if grass grubs are a problem in the district. One of the worst grass weeds which appears in garden areas is an annual, Poa annua. It flowers and seeds while the plant is very young and small and consequently the mower does not remove the seed heads. There may be several crops of this pale green grass each season, mostly during winter. It can cover gravel paths, and bare lawns for several months during winter and spring, but dies out to leave bare patches on the lawns during summer. The presence of this weed does not indicate that the soil is either too acid or too alkaline, as the grass will grow under either condition where the fertility of the soil is low. On lawns the fertility can be raised by the regular application of the fertilisers mentioned at least twice each year in spring and summer. It is preferable to apply them every three months. On paths an application of dalapon at 1 oz to 120 square yards could be used to destroy Poa annua. Hedge Plants Several ornamental plants such as escallonia and Chaenomeles japonica (japonica) are now being used as hedge plants and should be clipped back after flowering. Privet, lonicera, macrocarpa, and euonymus should also be pruned at this time. Hedges of Shawia paniculata (golden akeaks) are sometimes disfigured by the olearia gall midge, which causes stunting, resetting, and malformation of the leaves. Plants are best trimmed back during winter and sprayed now

with nicotine sulphate or DDT emulsion. Phebalium hedges have often been damaged by boring insects and where boring holes are noticed in these and any other trees, petrol could be squirted into the holes before they are sealed with clay or plugged with a twig. Phebalium is also susceptible to attack by root-rotting fungi, especially where conditions are inclined to be damp. The trees should be planted only where drainage is excellent. If the hedge starts to die out for no visible reason in one area, it may be possible to restrict the damage to that area by drenching the soil with 6 oz of copper oxychloride in 3 gallons of water per square yard. Lonicera nitida and many other plants are also susceptible to this trouble. Climbing Plants Evergreen climbers including the climbing potato vine Solanum jasminoides, ficus, and ivy can be pruned back into position : now. All climbing plants thrive best where there is adequate support. Plastic covered flex can be used to construct a cheap and artistic support which will not rust. In new gardens use should be made of annual climbing plants such as Mina lobata, tropaeolum (canary creeper) , sweet peas, and ipomea (morning glory) to give quick coverage of bare walls and early interest in the garden. Shrubbery Subtropical or tender plants and evergreens which would receive too much shock if planted out in the coldest months can now be planted. All shrubs should be lightly forked round and given a dressing of a balanced fertiliser such as that suggested for use on the flower border. Native trees can now be lightly pruned to retain their shape. When flowering is finished prunus, kerria, diosma, waratah, coleonema, tamarix, lilac, and spartium can be pruned. The waratahs should be sprayed with malathion or summer oil to prevent a build-up of scale insects. In windy places the young shoots from the base of this plant should be staked. Boronia plants are naturally short lived, but premature death can often be avoided if the plants are sprayed with malathion or DDT emulsion to kill the insects on whose excreta a black sooty mould appears. Fireblight Fireblight has caused damage in many areas throughout the country in the past season. This bacterial disease attacks a number of plants in the Rosaceae family including cotoneaster, pyracantha, flowering apples, rowan,

and hawthorn, as well as fruiting apples, pears, and quinces. Bees and other insects usually spread the disease from old infected wood when the flowers are in bloom. The first symptom is a darkening of the flowers and young twigs which typically turn brown and remain attached to the stem. As the disease is also spread by rain splash and winter pruning, the removal of any diseased wood or general pruning on these plants should be undertaken now during dry weather. Expensive sprays of streptomycin have been used with some success during . the blossom period to prevent spread of the disease. Rhododendrons and Azaleas Rhododendrons and azaleas may still be selected while in bloom in the shops and planted out. They require shelter from strong winds and prefer light shade for part of the day. After planting, a mulch of sawdust, to which sulphate of ammonia or blood and bone has been added, should be applied. In the early stages of the life of these plants, and especially with R. fragrantissimum and R. indicum, the young shoots should be nipped back often during the growing season to encourage a bushier habit. The foliage of the evergreen azaleas is sometimes infected by a fungous disease, azalea leaf gall. Affected leaves look blistered at this season. They should be picked off and the plants sprayed with a copper fungicide.

Several leaf spots occur on rhododendrons, especially ’ when growing under adverse . conditions. Spotted leaves should be' removed, conditions improved, and the plant sprayed with a fungicide such as thiram. Under Glass Plants which remain in the same pot for several years should be overhauled now. Those requiring repotting should be tipped out of old pots, the loose soil removed from the root area, and the roots lightly pruned ' before repotting. The top growth should be reduced to correspond with the root pruning. The surface of the pots of plants not being repotted should be scarified to remove moss and lighten the soil and then topdressed with a good soil mixture. The dead bark should be picked off fuchsias and a malathion spray applied if mealy bugs are present. All old pots should be scrubbed clean and dipped in a very weak bluestone mixture to prevent growth of algae. Begonia and gloxinia tubers being started into growth should be dusted with sulphur to combat mites, which have given considerable trouble in the last few years. Their starting media should be kept only slightly moist. Seed of glasshouse plants such as begonia, streptocarpus, coleus, and gloxinia can now be sown. General Cyclamen flowers should be removed to prolong flowering. Cuttings of Abutilon megapotamicum, tradescantia, double lobelia, and coleus can be rooted for growing indoors. Under cloches seed of asters can be sown direct into the ground. The plants grown this way are not so predisposed to the wilt fungus as those which are transplanted. Old plants of fibrous begonia can be broken up and planted out under cloches. These usually make taller plants than young seedlings. Water lilies can now be lifted and divided if necessary. Rose pruning should be finished immediately. The plants should be sprayed regularly against mildew, aphids, and caterpillars. A suitable combination spray can be made using 1 oz of 50 per cent captan or thiram t oz of 75 per cent colloidal sulphur wettable powder i oz of malathion powder 4 gallons of water Many plants such as magnolias and rhododendrons can be layered now into the soil or into sphagnum moss in a polythene sleeve. The dead and dying leaves of Iris unguicularis (stylosa) can be removed to tidy up the plants. Hemerocallis will benefit from the addition of fertilisers and compost as growth starts.

By I

ROSALIE A. CAMPION,

Horticultural Instructor, Department of Agriculture, Wellington

Cape Tulip Cape tulip (Homeria coHina), in flower this month, appears to be grown in many gardens in New Zealand. All parts of this bulbous plant are poisonous and it should be destroyed. The flowers may be salmon with a lemon centre or pure lemon. They open consecutively up the 3 ft stem. The bulbs are up to l| in. wide and covered with a mesh of fibre. The plant typically has only one leaf per bulb. This leaf is straplike and may be up to 3 ft long.

The whole plant should be lifted and burnt. Well established plants are very difficult to remove completely, as the young bulbs are very small. The place where the plants were removed from should be left vacant for at least two years, as some of the bulbs may remain dormant for a season, and grow the next.

A spray of 2,4-D plus diesel fuel is recommended for heavy infestations where it is possible to use this without damaging other plants.