Roses grow best in a loamy soil, but few of us have a perfect loam for growing roses occurring naturally in our gardens. It is important to prepare the soil prior to planting roses no matter what kind of soil you have. If planting into clay soil, it is even more important to prepare the soil in order to provide good drainage to the new rose plant and avoid root rot.
Dig a hole, 12 inches deep, and twice the diameter of the root ball of the rose bush you are planting. Keep the soil in a pile to one side of the hole.
Dig a further 12 inches into the soil and keep that soil aside in a separate pile. This is called double digging, and is especially helpful in loosening heavy clay soils for rose planting, according to online resource Rose Magazine.
Loosen the soil at the bottom of the hole with the spade, and mix some gravel and humus into the soil. Around three or four handfuls of both should suffice, depending on the size of the hole.
Mix some humus and a little sand into both piles of soil that were dug out.
Place the rose plant into the hole, centring it, and adjusting the height so it is sitting at the same height as in its nursery pot.
Fill the bottom of the hole around the plant from the soil that was dug out first. Then fill the remainder of the hole around the plant from the pile of soil that was dug out second, essentially swapping the first two layers of soil over. Press the soil tightly around the rose plant, to ensure air bubbles are eliminated.
Water the new plant well with the hose or watering can.
Well composted organic matter can substitute for commercial humus, consider adding a bit of nitrogen to the mix if using composted organic matter, this will help it decompose further.
Do not add a lot of sand to the clay soil, the ratio should be around 20 per cent or less of sand. Adding too much sand can result in the sand settling into a concrete-like pan below the surface and trapping water, according to Rose Magazine.