Autumn roses are often the most perfect ones. Shorter days are a signal to roses to prepare for winter dormancy and the plants start converting sugar to starches and storing it in their stems for their spring growth, so it is important to feed them regularly; especially in the summer rainfall regions. In very cold regions, you should stop feeding by mid-March as this will harden them off against the cold. Lower daytime temperatures and reduced evaporation also mean that you can reduce the amount you water, while still ensuring good moisture in the soil.
Watch out for red spider in hot, dry regions.
In hot, humid regions, you can trim your roses lightly if necessary. Do not cut them short as they can produce their most beautiful blooms in autumn
Late summer and autumn are ideal times to plant new roses, when the soil is still warm enough for the plant to produce hair roots. Roses planted at this time will be ready to grow to their full potential in spring, and produce their first flush of blooms of the season.
Roses like excellent air circulation, but not a draughty windy site; and require at least 5 to 6 hours of sunlight a day. Do not plant them near to walls where the soil tends to be dry, or close to other large shrubs, whose roots will compete with the rose for moisture and food.
Roses are quite fussy about their soil. They will do best in light clay or loamy soil, but sandy soil should be enriched with lots of well-rotted manure or compost. Heavy clay can be loosened with basalt and acidic soil is best mixed with lime each year.
Prepare your planting holes very well, making them 1 1/2 times as wide as they are deep, +-60cm square and +-45cm deep. Remove the topsoil and put it one side before digging the rest of the hole. Mix the excavated soil with special rose compost, or well-rotted manure or compost, and a handful of bone meal.
Before planting roses into the garden, ensure that the soil in the planting bag is well watered and allowed to drain, so that it is neither too dry, nor too soggy. Do not plant roses deeper than they are already growing in the nursery bag, the bud union must be above ground level. Firm the soil down well before watering the plants thoroughly. Keep the new plants moist but not soggy. In very cold regions, mulch the roots after planting to protect them from freezing. Do not prune roses after you have planted them in autumn
Some info from SA Gardening
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