Changes in garden levels

I have felled two elm trees that died recently. Is their timber suitable for building steps in an informal part of the garden?

Elm is an ideal timber for many garden projects as it is highly resistant to rot. Log steps can be built in a number of ways, the easiest of which is to use lengths of trunk or stout branches set across the slope. Strip all bark and remove any snags or projections. Simply bed the timber to form risers, driving two stakes into the ground on the lower side to provide a secure anchor. The treads can be gravel, rammed soil or grass edged with tough ground-cover plants such as an ivy or rose-of-sharon (Hypericum calycinum) flopping over the edges and softening the outline.

I wish to build a retaining wall about 1 m (3 ¼ ft) high between two levels, the upper one to be planted with shrubs. I have a good supply of old railway sleepers. Would these be suitable?

Railway sleepers are almost indestructable and blend well into virtually any garden setting. Normally, foundations are minimal: simply excavate a trench the width of the sleepers and lay these end to end. Continue to build the wall in a simple stretcher bond so that vertical joints are avoided and drill holes through the sleepers as work progresses so that lengths of reinforcing rod can be passed through and driven securely into the ground when the wall is complete.

Although the patio at the rear of my house is well laid, the slabbed steps that descend from it have become unsafe. Can I repair these or should they be rebuilt?

If the problem is simply that the treads have become loose and wobble on the risers, the slabs can be carefully lifted and repositioned on a fresh bed of 3:1 mortar, making sure that there is a very slight cross-fall or slope so that the surface will shed water.

If the risers have deteriorated, however, the entire flight should be taken down and rebuilt. If the flight projects out from the patio, retaining walls in brick, stone, or blocks will be needed on either side, and these must be built on sound footings whose depth will depend on the type of ground. The risers should be about 150 mm (6 in) high, and the first riser in the flight should be built off a similar foundation, the space behind it being filled with compacted hardcore topped with a weak concrete mix. Bed each slab on mortar so that it overhangs its riser by about 50 mm (2 in); build the second riser off the rear of the first tread, the whole operation being repeated until the patio level is reached.

My patio is made of solid concrete and seems stark and uninteresting. As I cannot break through it to create planted areas, is there some other way I can soften the outline?

Planting is undoubtedly the answer, and pots and tubs filled with annuals would certainly give you instant, if rather shortlived, colour. Raised beds are a better alternative, helping to give the area definition as well as acting as occasional seats. As a general rule the bigger the bed the better, as this will prevent excessive drying out. Timber, brick, stone, or concrete blocks would all be suitable, though the last would tend to increase the existing monotony. As your patio has a firm base no footing will be necessary, but remember that you should leave a number of weep holes just above ground level for drainage. Put a 150 mm (6 in) layer of hardcore at the bottom of the bed and top up with good-quality topsoil.

I have a retaining wall 1.2 m (4 ft) high, but over the years the weight of soil has virtually pushed it over. I wish to rebuild it but I do not want the same problem to recur.

This is a common problem and nearly always means that the foundations are inadequate or that the wall is not thick enough. Take the old wall down and cut the bank back 600 mm (2 ft) from the face of the new wall, making sure you stack subsoil and topsoil separately. A wall 1.2 m (4 ft) high will need to be at least 225 mm (9 in) thick for safety and if the area tends to get waterlogged a 343 mm (13 ½ in) wall—the width of three clay bricks— will be safer. The foundations must be twice as thick as the wall and should be at least 450 mm (18 in) deep.

In order to give the wall added strength it can be built to a batter (leaning inward slightly), and the foundations can be finished at an angle to match this. If using brick, choose a hard well-fired variety and leave open joints (weep-holes) at regular intervals along the bottom course to allow drainage. When backfilling, a layer of hardcore should be placed first, followed by subsoil and at least 450 mm (18 in) of topsoil.

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