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I am posting for advice regarding two large rose beds I have been asked to redevelope. Each bed measures 24 x 4m and are currently planted with old poor quality roses, these have been at this location for many years, some as long as 40. As can be seen from the picture (taken this July) the roses look very sparse and are not flowering well. Hard pruning to rejuvenate has been tried, these roses then generally die. A complete re-plant is required. Tough English Roses will be planted having an average height of 1 to 1.2m with a central band of taller grasses such as Miscanthus, Molinia and Calamagrostis snaking through the middle of each bed to provide late summer interest and winter structure.

Honey Fungus has been creeping into the beds (fruiting bodies appear next to dead roses in the autumn). In addition to this I am aware of replant/rose sickness. Given the Honey Fungus and replant disease swapping for new sterilised soil is the preferred option. We will go down between 60cm to 1m. Around the edge of the bed thick plastic sheeting will be installed to prevent Rhizomorphs re-entering. This will be fitted down to the base of the new soil depth, and will be fixed to bed edging 5 or so cm above top soil level.

The topsoil is average/improved loam to a depth of around 50cm, below this heavy clay stoney subsoil. However, this soil profile dramatically changes including patches of more sandy soil. I believe this dates from the sites original construction (moving around/dumping of earth) in the 1930's.

However, a landscape contractor has told me that we cannot simple just put in 1m of topsoil; drainage issues would ensue. The beds are on the top of a bank so land drainage is a possibility by punching through this bank.

How far do we need to dig down/soil depth to remove for both the Honey Fungus and replant disease? If we were to go down a full metre would we need layers of hardcore/gravel at the base, how deep? (we would use this option if drainage pipes installed). What soil would be the best to purchase? Matching what is currently on site would be near impossible due to so much local variation.

I would rather over do the specifications, given the scale of the project it cannot fail, I'd have 250 very angry flat owners to deal with if it did! It is proposed that the roses will be moved/replaced on a 25 year cycle to keep this high profile area in tip top condition. In my own experience vigorous healthy plants will not succumb to honey fungus, especially if the site owners repeat the above procedure on a 25 year cycle.

Thanks, any advice greatly appreciated