HOME GARDENS

Bay of Plenty Beacon, Volume 12, Issue 86, 25 August 1948, Page 7

HOME GARDENS

(By J. W. Goodwin, N.D.H. (N.Z.), F.R.H.S., Massey Agricultural College.) THOSE RETAINING WALLS There have been several inquiries concerning retaining walls, and plants suitable to grow on them. There is no doubt that even a low wall is a great improvement to a garden on a bank or hillside. A wall will give larger, 'more level areas, and an impression that the area is greater. It will also provide plants with a suitable home from which there is little risk of the valuable surface soil being washed away. Bricks, concrete or stones cemented in concrete all make strong durable walls. There are two important essentials with these types. Firstly, the soil must be excavated at the base until a really solid foundation is reached. The actual depth and the thickness at the base really depends on the height of the wall and the nature of the ground. Where the ground is not really solid, a wide base, and even reinforcing, wiil be necessary to prevent cracking or subsidence, which spoils, many expensively constructed walls. The second point concerns the drainage from'behind these walls. Seep-holes should be made during construction, spacing them about five to eight feet apart along the walls, and one row to every three feet of height. These holes should be from 1J to 2 inches in diameter,

and were formerly made by setting short lengths of galvanised piping in the wall as it was built. Wooden plugs, were also used, being removed after the cement had set. If there is a considerable amount of seepage water, held behind a wall, the soil becomes unstable, and greater weight is the thrust on the wall, which, in extreme cases, will collapse. More important, from the plantsman’s point of view, is that waterlogged conditions mean that plant roots will not penetrate because of the lack of aeration. Plants planted at the top of these walls become surface-rooting and will suffer severely ' during the dry season. All walls should have a slight slope back towards the bank, and high walls require anchoring to the bank by means of “ties” of iron rods or concrete / extending back and secured in the soil by a “foot” of anchor cf larger size. These should be six feet apart. Another method is. to build the wall with stout buttresses every 6 to 8 feet to strengthen it. Breaking Severe Lines These walls are very formal and “furnishing” to break the Uniformity and fit in with the informal nature of flowering plants. A solid wall must be clothed either with climbers, taller perennials and shrubs growing up from the base, or with trailing plants hanging down from above. Probably a mixture of all types is the best treatment. Care must be taken that all plants are not decidous, leaving a bare effect in winter time. The second type of wall has become more prominent of recent years, mainly because of cement restrictions. -This is the “dry wall” which provides a home for many plants besides being a retaining wall. The stones are built up and packed with Soil, and these walls, when well built, are effective and last well. They can never be as strong as concrete, of course, but they are less costly to construct. This wall should also have a solid foundation, and the larger stones should be used for the base of the wall. All stones should dip slightly towards the back, and the face of the wall should slope b'ack very gradually and very evenly. The easiest way to do this is to build up to the first row above ground level, for the full length of the wall, on the desired line or curve. Next, place a line of. straight stakes aboirt 6 feet apart along the outside of these stones. These stakes may be lined up, giving the desired slope inwards and adjusted by sighting along them. It is then a comparatively simple matter to set to stone by glancing along the line of the two stakes ahead. Where fat stones are available the job is comparatively easy, but with broken rock or river stones it is necessary to fit the various shapes to the most suitable positions. Building up against a hard face is not recommended as there is always the possible danger of a collapse.