Soil Changing - a hard task; but a thorough way to combat soil-sickness
Dig out the soil to at least 1ft (30cm) and cart it away. The old soil is fine for other plants.
Fork peat and bonemeal into the base.
Refill with soil that has not grown roses. Extra organic matter (6X) will boost nutrient levels.
Pot-Sinking - a suitable option if gapping-up old beds, or if soil chaging isn't possible.
Pot the new rose into a (plastic) container of at least 15 litres volume.
Increase or expand drainage holes as roots will eventually grow through.
Dig a hole the right size to accommodate the container.
Fork organic manure, or peat and bonemeal, into the base of the hole.
Sink the pot into position, adjust depth, and firm in.
Less Drastic Measures - in cases where roses have not been growing for at lease 2 years, or if previous roses did not show signs of soil sickness, prepare several weeks ahead of planting as follows:
Dig the soil, incorporating 6X or similar organic nutrient.
Use the planting mixture of 95% peat and 5% bonemeal. Mix in the planting mixture by forking it into the bottom of the planting holes, and combine it with the soil used to fill in around the roots.